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LINQ is .NET Language-Integrated Query. It's included in .NET Framework 3.5 and you can use it in Visual Studio 2008 projects. XPO has officially supported LINQ since v7.3 and since then we have continued to improve and support it. Nowadays LINQ to XPO is very mature, extendable (How to: Implement Custom Functions and Criteria in LINQ to XPO) and powerful (Free Joins). In the latest version we make it even easier to use LINQ to XPO since we only distribute one assembly, DevExpress.XPO.dll, which includes everything! (custom providers as well).
XPO can talk transparently to a large list of database systems. It was already possible to make complex queries using our standard criteria syntax, however using LINQ offers some great advantages.
- No magic strings, like you have in standard criteria syntax,
- Intellisense support making it easier and faster to construct your queries,
- Compile time checking,
- Learning to write LINQ queries/lambdas is a must learn for .NET developers,
The benefits are clear, however there is a caveat when using LINQ. It is not possible to use Edit and Continue and with even the smallest change you need to restart your debugging session. As a result your development speed is decreased dramatically.
The solution as always is to use the right tool and in this case the right tool is LINQPad. It provides a flexible UI allowing you to use LINQ in various ways.
In our latest version our team released an XPO context driver for LINQPad. Let’s see how to configure it.
Firstly we need to install the driver found at C:\DevExpress 2011.2\Components\Tools\DXperience\XPOContextDriver.lpx.
Secondly we need to setup a new connection.
In this example we are going to use the MainDemo assembly containing the business objects.
LINQPad populated the domain in a hierarchical treelist. This allows us to enjoy using drag & drop plus intellisence in its expression editor to form the LINQ queries. Furthermore it is possible to use your style of language as demonstrated below.
The cool part is that LINQPad, written by the great Joe Albahari, is available for free. It is strongly recommended as a great way to learn LINQ.
Now for the fun part, let’s see it in action. Imagine we have the following code in our VS.
var queryable = from c in contacts
let tasks = c.Tasks.Where(t => t.ActualWork < 0)
where tasks.Any()
orderby c.LastName
select new {
c.LastName,
Orders = tasks.Count(),
};
We wish to see the results of queryable variable ,the best way to achieve this is to set a breakpoint then hit F5. Next we wait for our app to load and navigate to the action that will hit the breakpoint. Finally we must select the queryable variable and hit Shift+F9 to invoke the debugger window and examine the result set. Now we can try to make our requirements more complex. Lets say we also want to examine the result set when ActualWork>10. The solution is really easy when using LINQPad, we simply need to copy paste the code from VS to LINQPad the expression editor like this,
After this we can quickly and easily form queries as we wish and examine their result sets instantly. Using the excellent and cheap LINQPad Autocompletion it is possible to use VS like intelligence to further speed up your development.
PS: eXpandFrameWork contributors are already using the Autocompletion feature since LINQPad offered a license for its contributors.
We would appreciate your feedback on this post. Has it been useful to you? Feel free to contact us with any further questions
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At 11.00 PST on Thursday 15th December I will be appearing live on Scott Hanselman’s podcast Hanselminutes. During the course of the show Scott and I will be discussing eXpand framework and its relationship with XAF. Please tune in and show some support for your favorite frameworks! We built this thing together guys and this is an exciting event for all of us.
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WF4 uses a service oriented architecture and as a result any problem can be decoupled into smaller, easily solvable and testable services. XAF uses MVC architecture which, in a sense, is very similar to that used by WF4. We can compare XAF’s controllers to WF4 services. Moreover XAF’s Application does the same job as the WF4 server. The upshot of all this is that users should be able to get the feel of WF4 in no time at all. The XAF workflow module introduces a new layer that makes the already decoupled services aware of our business classes. After this the sky is the limit and over the next few posts I aim to demonstrate some of what can be achieved. For example the next post will focus on creating an event driven workflow initialization engine.
To get back to today’s post, we will discuss an implementation that is very decoupled and as a result it has very limited dependencies on other modules. It is worth noting that all XAF’s features are decoupled, persistent objects take on the role of domain mappers.
Take these requirements;
- an end user needs to be able to input an object type (and or) a property name,
- an object change needs to start the workflow either at client or at sever,
- workflows need to be aware of the object that has changed, its PropertyName and its property OldValue.
The custom workflow definition
We cannot use the default XAF XpoWorkFlowDefinition class in any way. This is because there are no fields to store the PropertyName and its OldValue. We should not even derive from the default XpoWorkFlowDefinition because we may face difficulties as this class is used by our workflow server. To cope with this issue it is necessary to create a custom ObjectChangedWorkflow definition as shown.
While we are doing this we also need to modify the default xaml of the workflow and add the two more arguments (propertyName, oldValue) as per our requirements.
Below you can see the UI of this custom workflow definition,
Up to here XAF has made things very straightforward for us. We have designed a normal persistent class to store our data and we have used attributes (PropertyEditorType, DataStourceProperty, TypeConverter etc) to configure the UI.
Registration of custom workflow definition
The next step is to register this custom workflow definition. To help with this task, eXpand, provides the WorkflowStartService<T> where T is the type of workflow. Furthermore for ObjectChangeWorkflow definitions the implementation is rather easy since there are no further requirements.
public class ObjectChangedWorkflowStartService : WorkflowStartService<ObjectChangedWorkflow> {
public ObjectChangedWorkflowStartService()
: base(TimeSpan.FromMinutes(1)) {
}
public ObjectChangedWorkflowStartService(TimeSpan requestsDetectionPeriod) : base(requestsDetectionPeriod) { }
protected override bool NeedToStartWorkflow(IObjectSpace objectSpace, ObjectChangedWorkflow workflow) {
return true;
}
protected override void AfterWorkFlowStarted(IObjectSpace objectSpace, ObjectChangedWorkflow workflow, Guid startWorkflow) {
}
}
Start workflow - Track Object Changes
Now, when I have registered workflows on the server, it's time to return to my task: start a workflow when a property has been changed.
In XAF, I can track changes with the help of the ObjectSpace.Committing and ObjectSpace.ObjectChanged events. However because we need to create only one request per object change, it is advisable to collect the changes in an array.
public class StartWorkflowOnObjectChangeController : ViewController<ObjectView> {
protected override void OnActivated() {
base.OnActivated();
if (TypeHasWorkflows()) {
ObjectSpace.ObjectChanged += PopulateObjectChangedEventArgs;
ObjectSpace.Committing += StartWorkFlows;
}
}
void PopulateObjectChangedEventArgs(object sender, ObjectChangedEventArgs objectChangedEventArgs) {
if (!string.IsNullOrEmpty(objectChangedEventArgs.PropertyName)) {
var changedEventArgs = _objectChangedEventArgses.FirstOrDefault(args => args.Object == objectChangedEventArgs.Object && args.PropertyName == objectChangedEventArgs.PropertyName);
if (changedEventArgs != null) {
_objectChangedEventArgses.Remove(changedEventArgs);
_objectChangedEventArgses.Add(new ObjectChangedEventArgs(changedEventArgs.Object, changedEventArgs.PropertyName, changedEventArgs.OldValue, objectChangedEventArgs.NewValue));
} else
_objectChangedEventArgses.Add(objectChangedEventArgs);
}
}
void StartWorkFlow(ObjectChangedEventArgs objectChangedEventArgs, ObjectChangedWorkflow objectChangedWorkflow) {
var o = objectChangedEventArgs.Object;
ITypeInfo typeInfo = XafTypesInfo.Instance.FindTypeInfo(o.GetType());
object targetObjectKey = typeInfo.KeyMember.GetValue(o);
if (objectChangedWorkflow.ExecutionDomain == ExecutionDomain.Server) {
CreateServerRequest(objectChangedEventArgs, objectChangedWorkflow, targetObjectKey, typeInfo);
} else {
InvokeOnClient(objectChangedEventArgs, objectChangedWorkflow, targetObjectKey);
}
}
As you will have noticed we have not used the default VS naming for ObjectSpace event handlers. This is because the names that have chosen give a more specific idea of how each method works.
The ObjectChanged event occurs each time a property is changed and the changes are collected in the objectChangedEventArgses array. The Committing event occurs once changes are ready to be sent to the server and workflows start for each entry. We have introduced two options for starting and executing workflows;
- Execute synchronously and locally,
- Send a request to the server and execute at the server asynchronously
Execute a workflow synchronously on the client
The next stage is to create activities at the client then on ObjectSpace CommitChanges from appropriate WorkflowDefinition and execute them immediatelly
public class StartWorkflowOnObjectChangeController : ViewController<ObjectView> {
void InvokeOnClient(ObjectChangedEventArgs objectChangedEventArgs, ObjectChangedWorkflow objectChangedWorkflow, object targetObjectKey) {
Activity activity = ActivityXamlServices.Load(new StringReader(objectChangedWorkflow.Xaml));
var dictionary = ObjectChangedStartWorkflowService.Dictionary(targetObjectKey, objectChangedEventArgs.PropertyName, objectChangedEventArgs.OldValue);
WorkflowInvoker.Invoke(activity, dictionary);
}
This is a simple code which can be found in nearly any WF4 example at
http://www.microsoft.com/download/en/details.aspx?id=21459.
Send a request to start workflow on the server
The second of our two methods involves starting the workflow at the server. Now we need to notify the server of the values of those arguments as well. In the manually starting workflows post we learnt that XAF does this by using XpoStartWorkflowRequest. This class has a different design however, and may create issues since it is used by XAF default services. Therefore instead of deriving from XpoStartWorkflowRequest we need to design a similar custom class.
public class ObjectChangedXpoStartWorkflowRequest : WFBaseObject, IObjectChangedWorkflowRequest {
[TypeConverter(typeof(StringToTypeConverter))]
public Type TargetObjectType {
get { return _targetObjectType; }
set { SetPropertyValue("TargetObjectType", ref _targetObjectType, value); }
}
#region IDCStartWorkflowRequest Members
public string TargetWorkflowUniqueId {
get { return GetPropertyValue<string>("TargetWorkflowUniqueId"); }
set { SetPropertyValue("TargetWorkflowUniqueId", value); }
}
[ValueConverter(typeof(KeyConverter))]
public object TargetObjectKey {
get { return GetPropertyValue<object>("TargetObjectKey"); }
set { SetPropertyValue<object>("TargetObjectKey", value); }
}
#endregion
#region IObjectChangedWorkflowRequest Members
public string PropertyName {
get { return _propertyName; }
set { SetPropertyValue("PropertyName", ref _propertyName, value); }
}
[ValueConverter(typeof(SerializableObjectConverter))]
[Size(SizeAttribute.Unlimited)]
public object OldValue {
get { return _oldValue; }
set { SetPropertyValue("OldValue", ref _oldValue, value); }
}
This is a very simple class, its only role is to store values in the database. Now instead of invoking workflows locally we only need to create ObjectChangedXpoStartWorkflowRequest objects.
public class StartWorkflowOnObjectChangeController : ViewController<ObjectView> {
void CreateServerRequest(ObjectChangedEventArgs objectChangedEventArgs, ObjectChangedWorkflow objectChangedWorkflow, object targetObjectKey, ITypeInfo typeInfo) {
var request = ObjectSpace.CreateObject<ObjectChangedXpoStartWorkflowRequest>();
request.TargetWorkflowUniqueId = objectChangedWorkflow.GetUniqueId();
request.TargetObjectType = typeInfo.Type;
request.TargetObjectKey = targetObjectKey;
request.PropertyName = objectChangedEventArgs.PropertyName;
request.OldValue = GetOldValue(objectChangedEventArgs);
}
In the next step we are going to create a service to consume these values from the server and start a workflow,
public class StartWorkflowOnObjectChangeService : BaseTimerService {
public override void OnTimer() {
using (var objectSpace = ObjectSpaceProvider.CreateObjectSpace()) {
//get all requests from the database
foreach (var request in objectSpace.GetObjects<ObjectChangedXpoStartWorkflowRequest>()) {
//find workflow
var definition = GetService<IWorkflowDefinitionProvider>().FindDefinition(request.TargetWorkflowUniqueId);
if (definition != null && definition.CanOpenHost) {
//Start the workflow passing in PropertyName && OldValue
if (GetService<ObjectChangedStartWorkflowService>().StartWorkflow(definition.Name,
request.TargetWorkflowUniqueId, request.TargetObjectKey, request.PropertyName, request.OldValue)) {
objectSpace.Delete(request);
objectSpace.CommitChanges();
}
}
}
}
}
At this point our server has all the information it needs to start workflows with arguments taken from persistent ObjectChangeXpoStartWorkFlowRequest objects.
I must admit that I have fully enjoyed preparing this post. The decoupled development experienced offered by the WF service oriented model is something that really appeals to me. At the same time XAF’s workflow module implementation made modeling the requirements a simple and enjoyable process. As usual it was possible to work directly on the problem and leave the hard work to non XAF developers.
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Prerequisites
Part 1
In this post we are going to enhance the State Machine module UI. Remember that along with all the usual XAF goodies we can now use Xpand code base which gives us a lot more options. Our StateMachineTransitionPermission has 2 lookups, StateMachineName and StateMachine. Our goal is to populate both of these cascading lookups without creating a platform specific module.
StateMachineNames
Creating lookups is a common scenario for which Xpand provides a set of property editors and controllers. By contrast with other business frameworks XAF allows maximum flexibility. Therefore in most cases we are able to code in such a generic way that everything could live in separate frameworks such as eXpand. Now, in order to populate the StateMachine name I am going to derive a new controller from a specialized abstract controller which is Xpand.ExpressApp.SystemModule.PopulateController<T>. This controller uses the PredefinedValues attribute of the XAF model. When filling the attribute with a set of values separated by semicolons XAF will create a lookup with these values targeting each supported platform.
However, if at runtime we set the value of the PredefinedValues attribute this will be written at model’s lastlayer and it will make it dirty. We want to avoid this because we want to leave the lastlayer intact.. To cater for this need the populate controller uses a hack. First it stores the lastlayer in a variable then removes it from the model’s layers collection. As a result it is possible to modify the new lastlayer as shown in the Populate method and then return the clean old one to its place. Now the model has all the necessary information with a clean userdiffs layer and while XAF is creating a new view can get the PredefinedValues string from it and create the lookups.
public abstract class PopulateController<T> : ViewController<ObjectView> {
…
…
protected virtual void Populate(Func<IModelMember, string> collect) {
var name = PropertyName;
if (name != null) {
var model = ((ModelApplicationBase)Application.Model);
var lastLayer = model.LastLayer;
model.RemoveLayer(lastLayer);
PopulateCore(collect, name);
model.AddLayer(lastLayer);
}
}
private void PopulateCore(Func<IModelMember, string> collect, string propertyName) {
IModelMember modelMember = View.Model.ModelClass.AllMembers.FirstOrDefault(member => member.Name == propertyName);
if (modelMember != null) {
modelMember.PredefinedValues = collect.Invoke(modelMember);
}
}
…
…
}
Although this seems like a complicated explanation users need not be intimidated! The implementation of our controller that will populate all StateMachineNames is as simple as this,
public class StateMachinePopulateController : PopulateController<StateMachineTransitionPermission> {
protected override string GetPredefinedValues(IModelMember wrapper) {
IList<XpoStateMachine> xpoStateMachines = ObjectSpace.GetObjects<XpoStateMachine>(null);
return xpoStateMachines.Select(machine => machine.Name).AggregateWith(";");
}
protected override Expression<Func<StateMachineTransitionPermission, object>> GetPropertyName() {
return permission => permission.StateMachineName;
}
}
The first thing we did was to provide the propertyName in the GetPropertyName method. Then using the GetPredifinedalues method we return the semincolon delimited string with the machine names. This very simple controller is capable of populating the statemachine lookup for win and web platforms!.
StateCaptions
This is a cascading lookup and as a result when the current StateMachineName changes it needs to provide a list of all its StateCaptions. To this end we are going to use a specialized property editor, Xpand’s StringLookupEditor. This supports the
DataSourceProperty XAF attribute which will be used to provide the StateCaption collection. Moreover when using Xpand it is possible to mark editors with an interface and host it in a transparent module. We can then use the Xpand PropertyEditor attribute with the type of the interface as parameter to tell XAF which propertyeditor will be created at runtime. Finally we need to apply all these along with an ImmediatePostData to the StateMachineName property. The permission will look like this,
[ImmediatePostData]
public string StateMachineName { get; set; }
//IStringLookupPropertyEditor lives in Xpand.ExpressApp assembly
//Xpand.ExpressApp.Web.PropertyEditors.StringLookupPropertyEditor, Xpand.ExpressApp.Win.PropertyEditors.StringLookupPropertyEditor inherit from IStringLookupPropertyEditor
[PropertyEditor(typeof(IStringLookupPropertyEditor))]
[DataSourceProperty("StateCaptions")]
public string StateCaption { get; set; }
IList<string> _stateCaptions = new List<string>();
[Browsable(false)]
public IList<string> StateCaptions {get {return _stateCaptions;}}
If you look carefully at this code however you may notice that __stateCaptions count is always zero. Let me remind you here that the StateMachineTransitionPermission is a non persistent sessionless object. This means that the object is not handled by an ObjectSpace therefore a call like ObjectSpace.FindObjectSpaceByObject(this) will always return null. In addition the permission does not implement INotifyPropertyChanged so we need to synchronize the class just before the StateCaptions are requested. Below you can see a modified version of the StateMachinePopulateController,
public class StateMachinePopulateController : PopulateController<StateMachineTransitionPermission> {
protected override void OnViewControlsCreated() {
base.OnViewControlsCreated();
var stringLookupPropertyEditor = GetPropertyEditor(permission => permission.StateCaption) as IStringLookupPropertyEditor;
if (stringLookupPropertyEditor != null)
stringLookupPropertyEditor.ItemsCalculating += StringLookupPropertyEditorOnItemsCalculating;
}
void StringLookupPropertyEditorOnItemsCalculating(object sender, HandledEventArgs handledEventArgs) {
var propertyEditor = GetPropertyEditor(permission => permission.StateMachineName);
if (propertyEditor != null && View.IsControlCreated) {
var stateMachineTransitionPermission = ((StateMachineTransitionPermission)View.CurrentObject);
var readOnlyCollection = GetStateCaptions(propertyEditor);
stateMachineTransitionPermission.SyncStateCaptions(readOnlyCollection, propertyEditor.ControlValue as string);
}
}
ReadOnlyCollection<string> GetStateCaptions(PropertyEditor propertyEditor) {
var stateMachineName = propertyEditor.ControlValue as string;
return ObjectSpace.GetObjects<XpoState>(state => state.StateMachine.Name == stateMachineName).Select(
state => state.Caption).ToList().AsReadOnly();
}
Finally we add the new SyncStateCaptions method and the full version of the permission will be,
[NonPersistent]
public class StateMachineTransitionPermission : PermissionBase {
…
…
[ImmediatePostData]
public string StateMachineName { get; set; }
[PropertyEditor(typeof(IStringLookupPropertyEditor))]
[DataSourceProperty("StateCaptions")]
public string StateCaption { get; set; }
IList<string> _stateCaptions = new List<string>();
[Browsable(false)]
public IList<string> StateCaptions {get {return _stateCaptions;}}
public void SyncStateCaptions(IList<string> stateCaptions, string machineName) {
StateMachineName = machineName;
_stateCaptions = stateCaptions;
}
}
To support platform independent cascading lookups we wrote only about 10 lines of code! This is proof of how much XAF architecture cuts down on development costs. The module can be downloaded from the Xpand download page and we are happy to hear your feedback. Remember that your questions are the best candidates for future posts!
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As promised in the previous post I will now attempt to provide a concise yet comprehensive look at the 5 possibilities that Xpand gives us when we want to create a calculated member. I will also provide discussion of the relative advantages and disadvantages of each approach. We can see all of them in action in Xpand FeatureCenter application. Remember it is only thanks to the fact that XAF/XPO have such a strong and flexible architecture that this is possible! We must also acknowledge that these approaches have evolved as a direct result of contributions from the XAF team and community.
1. The XPO way –>Using Code
Take a look at the CreateCalculabeMember extension method in the code below,
public class CreateRuntimeCalculatedFieldController : ViewController {
public override void CustomizeTypesInfo(DevExpress.ExpressApp.DC.ITypesInfo typesInfo) {
base.CustomizeTypesInfo(typesInfo);
XPClassInfo classInfo = XafTypesInfo.XpoTypeInfoSource.XPDictionary.GetClassInfo(typeof(Customer));
if (classInfo.FindMember("SumOfOrderTotals")==null) {
var attributes = new Attribute[] {new PersistentAliasAttribute("Orders.Sum(Total)")};
XPCustomMemberInfo calculabeMember = classInfo.CreateCalculabeMember("SumOfOrderTotals", typeof(float), attributes);
typesInfo.RefreshInfo(typeof(Customer));
}
}
}
XPO has a dictionary of domain metadata. The metadata of each persistent object is stored in XPClassInfo classes and the metadata of their properties is stored in XPMemberInfo classes. One of the main advantages of this approach is that it adds a new member to the XPO dictionary and therefore follows XAF to the letter. This is because in order to form the model XAF first queries the XPO dictionary and finally in order to configure the views it queries the model. Since we have worked in the data layer our calculated values will be sent to any data bound enabled control for rendering. The other benefit is that if we code there are no restrictions on what we can do, for example we can create members calling a WCF service. The sky’s the limit!
On the other hand each time we write new code we need to spend time testing and distributing it. Furthermore in certain scenarios problems can occur due to the fact that we add a new member to the object. For each new member we add to an object we are forced to deal with long properties lists in our model which can be somewhat unwieldy – imagine an object with 200 properties.
Note; XAF is smart enough to manage all of this without even breaking a sweat. This means that its performance does not suffer in any way. It is simply that this approach can leave the user with a bit of a headache!
2. Using the model
We have extended our model in order to describe all types of calculated and runtime properties.
Having done this makes it pretty easy to utilize the powerful XPO and add members in its dictionary as with the previous approach. This means this method shares some of the benefits we mentioned above. However as we are not writing code we can’t enjoy the same level of flexibility unless we utilize ModelUpdaters. Also as the columns can only be created using model editor they are only useful in situations when we have permission to modify the model. Finally we could end up with a huge number of properties here too for the same reason we identified previously.
All this is not to say that this approach doesn’t have its own unique advantages. For example the model difference can be stored in a database or xml file making it easy to distribute. To this end we can use the build in API or a specialized module like IO. Moreover it is possible to develop on site (client). Of course working at the model level allows us to use a model manager module like ModelDifference which is a great aid. It can be used to distribute the unbound columns to users, roles and even to other applications. In addition since ModelDifference supports both platforms it is possible to create calculated members without restarting the application or IIS.
3.WorldCreator extended members
This module maps the structure of the XPMemberInfo class to a persistent object. This approach is again similar to model approach (and once again has similar benefits) however there is a crucial difference. Instead of using the model to gather data to form the calculated members we use the input taken from the UI.
Using the UI is simplicity itself! It requires no technical knowledge whatsoever as the user is only required to choose from a set of basic options. We can still code if we wish, this time by creating persistent objects and then leaving eXpand to take care of the rest. That being said the real beauty of this approach is that the product can be developed on site without the user having to write a single line of code or using a sophisticated tool like Model Editor. Moreover we can enjoy ease of distribution due to the fact that our objects are stored in the database. As the metadata is now in the form of persistent objects locating it and working with it is as easy as ever.
By now it should be clear that as we are still relying on XPO we are faced with the same old problem regarding multiple views.
4. Using a WordCreator Dynamic Assembly
Our fourth approach uses the same module to create dynamic persistent assemblies using code generation templates. XAF is the best framework to describe domains which is evidenced by the way that WorldCreator maps the Assembly structure to persistent objects and auto generates a flexible UI.
Using the templates will create a dynamic assembly with exactly the same code and structure as if we had taken the time to design it ourselves inside VS. Distribution is still easy since is everything is in the database. The fact that we script at runtime means that our options are almost unlimited when taking this approach.
5. The Unbound Column
Extending the model with an Unbound column node as shown makes it possible to create Unbound grid columns and set their unbound expressions.
This is the only approach that allows us to work directly on views without utilizing XPO. This means that we gain the maximum level of flexibility since it is possible to have different columns for the same object views. Therefore we can work on this column independently. At the same time the end user can change the UnboundExpression at runtime using expression editor (windows only). When it comes to distribution we find the same advantages as we do whenever we deal with the model.
As with the second approach we lose some flexibility because we are not writing code but again we can get round this using ModelUpdaters. In addition our columns still cannot be used when we do not have permission to modify the model. Another disadvantage concerns the fact that XAF is designed to make all calculations in the data layer and send the values to controls by applying an MVC pattern. A few years after XAF was released, Microsoft built Silverlight featuring very similar architecture. Taking into account the various factors this has been recognized as the optimal approach. Although using Unbound columns allows us to work in a different way we need to write extra code to support each control (Tree, Pivot etc) because the calculations are performed in the UI.
We are happy to read your feedback about this!. Remember that your questions are the best candidates for future posts.
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Recently in Xpand forums Dionisis Soldatos raised a question about how unbound columns can be implemented with XAF. Unbound columns along with their UnboundExpression can be used for creating calculated fields even at runtime. Since we are talking about unbound grid columns it should be obvious that we will operate at the UI level by modifying the grid control columns. However lets do a deep dive inside XAF model to extend it as needed!
The Model
By now we are all used to XAF providing us with excellent out of the box solutions which negate the need for us to write hundredths of lines of code. This of course means money saved during developing and ultimately your product hits the market faster. Why spend time reinventing the wheel when the XAF team have already done the hard work for you?
XAF creates the model by reading the metadata of our classes, this model has 3 types of view. One of these is the ListView which can be displayed with data source enabled controls like Grid controls. ListView has columns which correspond to existing object properties metadata and when XAF creates a Grid at runtime it queries model’s ListView columns. It then creates and configures Grid columns from their attributes. These stages are well tested and it is preferable to use them in our solution and override the unnecessary stages. For example we could create a normal model column node using XAF default Add/Column menu. After the Grid column is created it we simply need a few lines of code to make it unbound and set its Unbound Expression.
In order to store this expression we still need to extend model’s ListView with an attribute. The model can be extended either by registering an interface at ModuleBase.ExtendModelInterfaces or by deriving it from an already registered interface. I am going to take the latter options by deriving from IModelColumn interface which I will explain as we go.
public interface IModelColumnUnbound : IModelColumn {
[Category("eXpand")]
bool ShowUnboundExpressionMenu { get; set; }
[Category("eXpand")]
[Required]
string UnboundExpression { get; set; }
}
XAF model editor is a highly sophisticated tool which has the capability to recognize that we extended the model. It then takes care of the vital step of adding an entry to the Add menu for creating Unbound columns.
Now it is possible to create a new type of column with 2 extra attributes as shown,
Moving on we need to set the mandatory PropertyName attribute shown above to an always existing object property name. Remember XAF requires this in order to behave as designed. To this end we are going to set as PropertyName the object’s key property name using this simple DomainLogic class,
[DomainLogic(typeof(IModelColumnUnbound))]
public class IModelColumnUnboundLogic {
public static string Get_PropertyName(IModelColumnUnbound columnUnbound) {
return ((IModelListView)columnUnbound.Parent.Parent).ModelClass.KeyProperty;
}
As a result (PropertyName, PropertyEditorType and Caption) attributes will be populated the next time we create a ColumnUnbound Node. However these will be fixed values and it is preferable to hide them from the end user. At the same time we need to mark Caption attribute as required and remove its default value. To do all of this we just need to extend our IModelColumnUnbound interface like this,
Note; Although PropertyName and Caption belong to IModelColumn using the new operator it is possible to override them!
We have now finished with the model modifications and for our ColumnUnbound nodes XAF by design will create a new column pointing back to object’s key property metadata.
The UI
A key benefit of XAF’s commitment to design patterns, specifically to the Single responsibility principle, is that it provides us with the model’s synchronizer classes. These can be used to synchronize our model with the control and vice versa. It is only necessary to derive from the abstract ModelSyncroniser<T,V> and implement ApplyModeCore method to synchronize the control and from SynchronizeModel to do the same with the model.
public class UnboundColumnSynchronizer: ModelSynchronizer<GridListEditor, IModelListView> {
public UnboundColumnSynchronizer(GridListEditor control, IModelListView model)
: base(control, model) {
}
protected override void ApplyModelCore() {
var xafGridColumns = GetXafGridColumns();
foreach (var column in xafGridColumns) {
var modelColumnUnbound = (IModelColumnUnbound)column.Model;
column.FieldName = modelColumnUnbound.Id;
column.UnboundType = UnboundColumnType.Object;
column.OptionsColumn.AllowEdit = false;
column.ShowUnboundExpressionMenu = modelColumnUnbound.ShowUnboundExpressionMenu;
column.UnboundExpression = modelColumnUnbound.UnboundExpression;
}
}
IEnumerable<XafGridColumn> GetXafGridColumns() {
IEnumerable<XafGridColumn> xafGridColumns =
Model.Columns.OfType<IModelColumnUnbound>().Select(
unbound => Control.GridView.Columns[unbound.PropertyName] as XafGridColumn).Where(column => column != null);
return xafGridColumns;
}
public override void SynchronizeModel() {
var xafGridColumns = GetXafGridColumns();
foreach (var xafGridColumn in xafGridColumns) {
((IModelColumnUnbound) xafGridColumn.Model).UnboundExpression = xafGridColumn.UnboundExpression;
}
}
}
The above code uses the GetXafGridColumns method to return the grid columns that correspond to IModelColumnUnbound nodes. The web implementation is very similar and can be found here.
All that is left is to register our UnboundColumnSynchronizer like this,
public class UnboundColumnController : ViewController<ListView> {
protected override void OnActivated() {
base.OnActivated();
var gridListEditor = View.Editor as GridListEditor;
if (gridListEditor != null)
gridListEditor.CreateCustomModelSynchronizer += GridListEditorOnCreateCustomModelSynchronizer;
}
void GridListEditorOnCreateCustomModelSynchronizer(object sender, CreateCustomModelSynchronizerEventArgs createCustomModelSynchronizerEventArgs) {
createCustomModelSynchronizerEventArgs.ModelSynchronizer = new UnboundColumnSynchronizer((GridListEditor)sender, View.Model);
}
}
Note; Setting ShowUnboundExpressionMenu to true is only supported by Windows platform. There, an end user can modify the UnBoundExpression by invoking Grid’s expression editor
Together with the unbound column Xpand allows for up to 5 different approaches to creating calculated fields. In the next post we will discuss the pros and cons of each approach so stay tuned!
-
In version 11.1.7 our team now provides workflow instance support outside XAF borders! With a few lines of code, it is now possible to store our workflows in any of the 14 database systems described in this post.
Durability is a key benefit of the Workflow Foundation and it is based on the ability to store a running workflow instance on the fly at almost any time.
To this end Microsoft workflow team implemented the SqlWokflowInstanceStore class. Using this class and a few lines is possible to store workflow instances in SQL Server as shown,
// Define SqlWorkflowInstanceStoreBehavior:
// Set interval to renew instance lock to 5 seconds.
// Set interval to check for runnable instances to 2 seconds.
// Instance Store does not keep instances after it is completed.
// Select exponential back-off algorithm when retrying to load a locked instance.
// Instance state information is compressed using the GZip compressing algorithm.
SqlWorkflowInstanceStoreBehavior instanceStoreBehavior = new SqlWorkflowInstanceStoreBehavior(connectionString);
instanceStoreBehavior.HostLockRenewalPeriod = new TimeSpan(0, 0, 5);
instanceStoreBehavior.RunnableInstancesDetectionPeriod = new TimeSpan(0, 0, 2);
instanceStoreBehavior.InstanceCompletionAction = InstanceCompletionAction.DeleteAll;
instanceStoreBehavior.InstanceLockedExceptionAction = InstanceLockedExceptionAction.AggressiveRetry;
instanceStoreBehavior.InstanceEncodingOption = InstanceEncodingOption.GZip;
host.Description.Behaviors.Add(instanceStoreBehavior);
The above code was copied from the "BuiltInConfiguration" demo, "InstanceStore1" project. This demo is described at "Built-in Configuration"
(http://msdn.microsoft.com/en-us/library/ee622978.aspx). You can download full sources of this demo and many others at "WCF and WF Samples for .NET Framework 4"
(http://www.microsoft.com/download/en/details.aspx?id=21459).
Following the same architecture our team implemented the DX WorkFlow Instance Store. eXpress Persistent Objects (XPO) is used for common objects storage and is fully capable of working transparently with 14 different database systems. For example to provide support for an Oracle database we could write,
//We create or connect to a database by setting the connectionstring
//This code will create 2 tables (XpoWorkflowInstance, XpoInstanceKeyc) in the database
using (var session = new Session()) {
session.ConnectionString = "Data Source=DevExpressInstanceStore;User Id=myUsername;Password=myPassword";
session.UpdateSchema(typeof(XpoWorkflowInstance), typeof(XpoInstanceKey));
session.CreateObjectTypeRecords(typeof(XpoWorkflowInstance), typeof(XpoInstanceKey));
}
// Define WorkflowInstanceStoreBehavior:
var dxInstanceStoreBehavior = new WorkflowInstanceStoreBehavior(
typeof(XpoWorkflowInstance), typeof(XpoInstanceKey), DevExpressConnectionString);
host.Description.Behaviors.Add(dxInstanceStoreBehavior);
dxInstanceStoreBehavior.RunnableInstancesDetectionPeriod = new TimeSpan(0, 0, 2);
dxInstanceStoreBehavior.InstanceCompletionAction = InstanceCompletionAction.DeleteAll;
You can download a modified version of the “BuiltInConfiguration” solution here. The console application starts a long running workflow that implements a counting service. Once the service’s start method is invoked, the service counts from 0 to 59. The counter is incremented every 2 seconds. After each count the workflow persists so you can close the application at any time and when you start it next time it will continue. A new one will be started from '0' value in addition to the loaded instances. The second project “InstanceStore2” in the solution provides the same functionality, however it is configured using the app.config file as shown,
<system.serviceModel>
<extensions>
<behaviorExtensions>
<add name="DevExpressWorkflowInstanceStore" type="DevExpress.Workflow.Store.WorkflowInstanceStoreElement, DevExpress.Workflow.Activities.v11.1"/>
</behaviorExtensions>
</extensions>
<services>
<service name="CountingWorkflow" behaviorConfiguration="">
</service>
</services>
<behaviors>
<serviceBehaviors>
<behavior name="">
<!--<sqlWorkflowInstanceStore
connectionString="Data Source=.\SQLEXPRESS;Initial Catalog=InstanceStore;Integrated Security=True;Asynchronous Processing=True"
hostLockRenewalPeriod="00:00:05" runnableInstancesDetectionPeriod="00:00:02" instanceCompletionAction="DeleteAll"
instanceLockedExceptionAction="AggressiveRetry" instanceEncodingOption="GZip"
/>-->
<DevExpressWorkflowInstanceStore
connectionString="Data Source=DevExpressInstanceStore;User Id=myUsername;Password=myPassword"
runnableInstancesDetectionPeriod="00:00:02" instanceCompletionAction="DeleteAll"/>
</behavior>
</serviceBehaviors>
</behaviors>
</system.serviceModel>
Note; All we need to do to use these code snippets in our code is to reference 'DevExpress.ExpressApp.v11.1.dll' and 'DevExpress.Workflow.Activities.v11.1.dl assemblies. Even though these assemblies are part of our eXpressApp framework they can also be used to support any other type of .NET application!
We are waiting to read your feedback about this. Remember that your questions are the best candidates for future posts.
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-
In this post we are going to extend the functionality of the workflow module. to create a UI that will help us to schedule workflows. Some of you may recall that we looked at using a Delay inside a While activity in Working with CRUD activities – Short Transactions. Recently, DX-Squad member Martin Praxmarer raised an interesting question relating to this topic:
I have the requirement to do a workflow which starts each day on 6 clock - searches for orderdocuments where a specific date is less then X days. I know I will do an do while loop, but workflow definition has 2 options, start when new object, start when criteria, so when do i start this Workflow?
In order to achieve this we will use the WorkFlow demo that ships with our framework. The first thing is to design our custom ScheduledWorkflow persistent object by implementing IWorkflowDefinition. We didn’t derive it from the existing WorkFlowDefinition object because it has properties like TargetObjectType and start up conditions.
public enum StartMode {
OneTime,
Daily,
Weekly
}
[DefaultClassOptions]
[Appearance("WeekDays", "StartMode <> 'Weekly'",
TargetItems = "RecurEveryWeeks;Moday;Tuesday;Wednesday;Thursday;Friday;Saturday;Sunday",
Visibility = ViewItemVisibility.Hide)]
public class ScheduledWorkflow : BaseObject, IWorkflowDefinition {
public ScheduledWorkflow(Session session)
: base(session) {
}
public bool IsActive {
get { return GetPropertyValue<bool>("IsActive"); }
set { SetPropertyValue("IsActive", value); }
}
public bool RuntASAPIfScheduledStartIsMissed {
get { return GetPropertyValue<bool>("RuntASAPIfScheduledStartIsMissed"); }
set { SetPropertyValue("RuntASAPIfScheduledStartIsMissed", value); }
}
[Association]
public XPCollection<ScheduledWorkflowLaunchHistory> LaunchHistoryItems {
get { return GetCollection<ScheduledWorkflowLaunchHistory>("LaunchHistoryItems"); }
}
[ImmediatePostData]
public StartMode StartMode {
get { return GetPropertyValue<StartMode>("StartMode"); }
set { SetPropertyValue("StartMode", value); }
}
public TimeSpan StartTime {
get { return GetPropertyValue<TimeSpan>("StartTime"); }
set { SetPropertyValue("StartTime", value); }
}
[Appearance("RecurEveryDays", "StartMode <> 'Daily'", Visibility = ViewItemVisibility.Hide)]
public int RecurEveryDays {
get { return GetPropertyValue<int>("RecurEveryDays"); }
set { SetPropertyValue("RecurEveryDays", value); }
}
public int RecurEveryWeeks {
get { return GetPropertyValue<int>("RecurEveryWeeks"); }
set { SetPropertyValue("RecurEveryWeeks", value); }
}
public bool Moday {
get { return GetPropertyValue<bool>("Moday"); }
set { SetPropertyValue("Moday", value); }
}
public bool Tuesday {
get { return GetPropertyValue<bool>("Tuesday"); }
set { SetPropertyValue("Tuesday", value); }
}
public bool Wednesday {
get { return GetPropertyValue<bool>("Wednesday"); }
set { SetPropertyValue("Wednesday", value); }
}
public bool Thursday {
get { return GetPropertyValue<bool>("Thursday"); }
set { SetPropertyValue("Thursday", value); }
}
public bool Friday {
get { return GetPropertyValue<bool>("Friday"); }
set { SetPropertyValue("Friday", value); }
}
public bool Saturday {
get { return GetPropertyValue<bool>("Moday"); }
set { SetPropertyValue("Saturday", value); }
}
public bool Sunday {
get { return GetPropertyValue<bool>("Sunday"); }
set { SetPropertyValue("Sunday", value); }
}
#region IWorkflowDefinition Members
public string GetActivityTypeName() {
return GetUniqueId();
}
public IList<IStartWorkflowCondition> GetConditions() {
return new IStartWorkflowCondition[0];
}
public string GetUniqueId() {
if (Session.IsNewObject(this)) {
throw new InvalidOperationException();
}
return "ScheduledWorkflow" + Oid.ToString().ToUpper().Replace("-", "_");
}
[Browsable(false)]
public bool CanCompile {
get { return false; }
}
[Browsable(false)]
public bool CanOpenHost {
get { return IsActive && !string.IsNullOrEmpty(Name); }
}
public string Name {
get { return GetPropertyValue<string>("Name"); }
set { SetPropertyValue("Name", value); }
}
[Size(SizeAttribute.Unlimited)]
public string Xaml {
get { return GetPropertyValue<string>("Xaml"); }
set { SetPropertyValue("Xaml", value); }
}
#endregion
public override void AfterConstruction() {
base.AfterConstruction();
Xaml = DCWorkflowDefinitionLogic.InitialXaml;
}
}
In the above class we have added some scheduled specific properties such as StartMode, StartTime, RecurEveryDays etc. The class has been decorated with the Appearance attribute to control the visibility of the Day properties. This means when StartMode <> 'Weekly these properties will be hidden.
Moreover there is a collection LaunchHistoryItems of ScheduledWorkflowLaunchHistory objects, which will be used later to check if the workflow has been launched.
public class ScheduledWorkflowLaunchHistory : BaseObject {
public ScheduledWorkflowLaunchHistory(Session session) : base(session) {}
public DateTime LaunchedOn {
get { return GetPropertyValue<DateTime>("LaunchedOn"); }
set { SetPropertyValue<DateTime>("LaunchedOn", value); }
}
[Association]
public ScheduledWorkflow Workflow {
get { return GetPropertyValue<ScheduledWorkflow>("Workflow"); }
set { SetPropertyValue<ScheduledWorkflow>("Workflow", value); }
}
}
After designing these classes, we now have all the required input in order to schedule our workflows.
The next step is to load our custom workflows by extending the workflow provider service as shown,
public class ScheduledWorkflowDefinitionProvider : WorkflowDefinitionProvider {
public ScheduledWorkflowDefinitionProvider(Type workflowDefinitionType) : base(workflowDefinitionType) { }
public ScheduledWorkflowDefinitionProvider(Type workflowDefinitionType, IObjectSpaceProvider objectSpaceProvider) : base(workflowDefinitionType, objectSpaceProvider) { }
public override IList<IWorkflowDefinition> GetDefinitions() {
IList<IWorkflowDefinition> result = base.GetDefinitions();
IObjectSpace objectSpace = ObjectSpaceProvider.CreateObjectSpace(); //don't dispose immediately
foreach(ScheduledWorkflow workflow in objectSpace.GetObjects<ScheduledWorkflow>()) {
result.Add(workflow);
}
return result;
}
}
After this we are ready to implement our final service that will schedule our workflows,
public class ScheduledWorkflowStartService : BaseTimerService {
private bool NeedToStartWorkflow(IObjectSpace objectSpace, ScheduledWorkflow workflow) {
if (workflow.StartMode == StartMode.OneTime) {
if (workflow.LaunchHistoryItems.Count == 0) {
return true;
}
} else if (workflow.StartMode == StartMode.Daily) {
var historyItem = objectSpace.FindObject<ScheduledWorkflowLaunchHistory>(CriteriaOperator.Parse("GetDate(LaunchedOn) = ?", DateTime.Today));
if (historyItem == null && DateTime.Now.TimeOfDay > workflow.StartTime) {
return true;
}
} else if (workflow.StartMode == StartMode.Weekly) {
throw new NotImplementedException();
}
return false;
}
public ScheduledWorkflowStartService()
: base(TimeSpan.FromMinutes(1)) {
}
public ScheduledWorkflowStartService(TimeSpan requestsDetectionPeriod) : base(requestsDetectionPeriod) { }
public override void OnTimer() {
using (IObjectSpace objectSpace = ObjectSpaceProvider.CreateObjectSpace()) {
foreach (ScheduledWorkflow workflow in objectSpace.GetObjects<ScheduledWorkflow>(new BinaryOperator("IsActive", true))) {
WorkflowHost host;
if (HostManager.Hosts.TryGetValue(workflow.GetUniqueId(), out host)) {
if (NeedToStartWorkflow(objectSpace, workflow)) {
host.StartWorkflow(new Dictionary<string, object>());
var historyItem = objectSpace.CreateObject<ScheduledWorkflowLaunchHistory>();
historyItem.Workflow = workflow;
historyItem.LaunchedOn = DateTime.Now;
objectSpace.CommitChanges();
}
}
}
}
}
}
Note; the service is not fully implemented, however its very easy to continue from this point. This code will live in the new Xpand.ExpressApp.Workflow module. Now, for the rest of the implementation I would like to ask the help of our community. Anyone that wants to finish it contribute it is most welcome!
Finally we modify the WorkflowServerStarter class and add this service,
private void Start_(string connectionString, string applicationName) {
ServerApplication serverApplication = new ServerApplication();
serverApplication.ApplicationName = applicationName;
serverApplication.Modules.Add(new WorkflowDemoModule());
serverApplication.ConnectionString = connectionString;
serverApplication.Security = new SecurityComplex<User, Role>(
new WorkflowServerAuthentication(new BinaryOperator("UserName", "WorkflowService")));
serverApplication.Setup();
serverApplication.Logon();
IObjectSpaceProvider objectSpaceProvider = serverApplication.ObjectSpaceProvider;
server = new WorkflowServer("http://localhost:46232", objectSpaceProvider, objectSpaceProvider);
server.WorkflowDefinitionProvider = new ScheduledWorkflowDefinitionProvider(typeof(XpoWorkflowDefinition));
//Add the service
server.ServiceProvider.AddService(new ScheduledWorkflowStartService());
We are now ready to go!
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-
Our profiler uses WCF in order to communicate with the client application. One of the benefits of the XPOProfiler is that it supports 2 binding types. Both binding types have their advantages however in this situation only one allows us the flexibility we require.
NetTcpBinding
This option provides a secure and reliable binding environment for .Net to .Net cross machine communication. By default it creates a communication stack using WS-ReliableMessaging protocol, TCP for message delivery and windows security for message and authentication at run time.
One drawback is that in shared host environments there is no way to open a port neither to use Mutexes. Our second option allows us to overcome this by creating a WCF service and hosting it with our web application.
WSHttpBinding
-
Defines a secure, reliable, interoperable binding suitable for non-duplex service contracts,
-
Supports WS-* functionality and distributed transactions with reliable and secure sessions using SOAP security,
-
Uses HTTP and HTTPS transport for communication,
-
Reliable sessions are disabled by default
We have already identified limitations when profiling medium trust web applications, now we must look at modifying our application in order to overcome them.
The first step is to add the new service using VS add new Item context menu.
This action will add the following items to the project;
-
IMyLogService.cs - the communication interface description,
-
MyLogService.svc.cs - the communication service class declaration
Furthermore the Web.config file will be modified by adding <system.serviceModel> section. I am using .NET3.5 right now, be aware that this step may vary according to the .NET version you are using.
The next step is to remove the IMyLogService.cs from the project.
Then we are going to modify the MyLogService.svc.cs as follows;
[ServiceBehavior(InstanceContextMode = InstanceContextMode.Single)]
public class MyLogService : LogService {
public MyLogService()
: base(Logger) {
if (Logger != null) LogManager.SetTransport(Logger);
}
private static LoggerBase Logger {
get { return new LoggerBase(); }
}
}
The final step is to change the name of the communication contract in <system.serviceModel> section of Web.config file from WebApplicationToProfile.IMyLogService to DevExpress.Xpo.Logger.Transport.ILogSource.
After that we are ready to run the XPOProfiler and create a new connection to our medium hosted XPO web application.
Note: Version 11.2 will allow us to carry out all the above processes.
Happy profiling!
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-
The .NET Framework 4 ships with the SQL Workflow Instance Store which allows workflows to persist state information about workflow instances in a SQL Server 2005 or SQL Server 2008 database. However its implementation is based on stored procedures which can be a bit scary if you are not familiar with them. In addition our customers may follow different standards (Oracle, Firebird, VistaDB, MySQL, PostgreSQL etc.) and it’s unrealistic to hire more people to support SQL Server infrastructure.
Usually when dealing with these issues the first thing we do is to carry out a Google search for storage solutions. Surprisingly there is no such solution out there! Moreover there is very little useful code or samples available. Luckily XAF provides us with an easier route!
XAF is the perfect workflow modeling environment. It provides a ready made solution for creating and deploying a server that will execute workflows as described here. In order to start modeling workflows we can use VS design time along with our re-hosted runtime Workflow designer and custom WF4 activities. XAF also gives us increased control over our workflows for example through the ability to manually start workflows. Finally since XAF uses XPO to access data we can easily support 16 different database systems simply by providing a connection string!
| XPO Data Store Adapter | XPO Data Store Adapter's Assembly Name | Database Provider Assembly |
| AccessConnectionProvider | DevExpress.Xpo.vXXX | System.Data.dll |
| AdvantageConnectionProvider | DevExpress.Xpo.vXXX.Providers | Advantage.Data.Provider.dll 9.10.2.0 |
| AsaConnectionProvider | DevExpress.Xpo.vXXX.Providers | iAnywhere.Data.SQLAnywhere.dll 11.0.0.12642 |
| AseConnectionProvider | DevExpress.Xpo.vXXX.Providers | Sybase.Data.AseClient.dll 1.15.50.0 |
| DB2ConnectionProvider | DevExpress.Xpo.vXXX.Providers | IBM.Data.DB2.dll 9.5.2.2 |
| FirebirdConnectionProvider | DevExpress.Xpo.vXXX.Providers | FirebirdSql.Data.Firebird.dll 1.7.1.0
FirebirdSql.Data.FirebirdClient.dll 2.5.1.0 |
| MSSqlConnectionProvider | DevExpress.Xpo.vXXX | System.Data.dll |
| MSSqlCEConnectionProvider | DevExpress.Xpo.vXXX.Providers | System.Data.SqlServerCe.dll 3.5.0
System.Data.SqlServerCe.dll 4.0.8482.1 |
| MySqlConnectionProvider | DevExpress.Xpo.vXXX.Providers | MySql.Data.dll 5.2.5.0 |
| OracleConnectionProvider | DevExpress.Xpo.vXXX.Providers | System.Data.OracleClient.dll 2.0.0.0
Oracle.DataAccess.dll 9.2.0.700 |
| ODPConnectionProvider | DevExpress.Xpo.vXXX.Providers | Oracle.DataAccess.dll 10.1.0.200 |
| PervasiveSqlConnectionProvider | DevExpress.Xpo.vXXX.Providers | Pervasive.Data.SqlClient.dll 2.10.0.15 |
| PostgreSqlConnectionProvider | DevExpress.Xpo.vXXX.Providers | Npgsql.dll 2.0.11.0 |
| SQLiteConnectionProvider | DevExpress.Xpo.vXXX.Providers | System.Data.SQLite.dll 1.0.61.0 |
| VistaDBConnectionProvider | DevExpress.Xpo.vXXX.Providers | VistaDB.4.dll 4.0.0.0 |
More info @ Database Systems Supported by XPO
This is only one example of what XAF can do for us. XAF provides a comprehensive set of solutions that allow you to outsource all of the mundane programming tasks leaving you to focus purely on your business needs. For more info consult our docs, blogs, code central and support center.
Happy Workflowing!
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-
Let me describe for a moment how we at DX work. We build and sell software which means that we only sell and provide support for products that have been built and tested by us! However I am here as a framework evangelist and huge XAF fan. This makes it my duty to spread the word as much as I can and make XAF even bigger. To this end through collaboration within the XAF community, we have been building and supporting eXpand. This framework follows XAF to the letter and takes things even further. eXpand gets its inspiration from real life situations and bases itself on examples from DX SUPPORT CENTER. eXpand is the first open source project based on the DevExpress eXpressApp Framework (XAF). More info is available at www.expandframework.com and our very existence relies on your efforts! Anyone is welcome to contribute and enjoy the rewards. It is not necessary to be a XAF guru, we can all manage to create a behavior taken from DevExpress code central. Let’s work together to enhance our beloved XAF!
Today we are going to deal with creating a reusable module for eXpandFramework. This new module will host State Machine logic therefore we are going to name it Xpand.ExpressApp.StateMachine. A Security logic similar to this is going to be the first resident however we are going to use permissions rather than manually writing the custom function criteria operator to the TargetObjectCriteria. This module can be used as a standalone without the need of eXpandFramwork for the moment. However keeping it under the eXpand umbrella will help us to share features/processes within the framework in the future.
First we need to create a new VS project that shares characteristics with the rest of the eXpand modules. Currently eXpand only provides a new Solution VS template. This means that we need to do things the old fashioned way, i.e. copying and pasting an existing module. Our behavior is platform independent thus it’s a good idea to choose a module that is also platform independent such as Xpand.ExpressApp.ViewVariants.
The next step is to open the cloned project, rename it and set its references to those shown in the pic below. It is important to leave all Xpand core references as they are.
It is advisable to register the original StateMachine module to avoid having to register it later.
XpandSystemModule is already registered since we used the Xpand.ExpressApp.ViewVarians project as a template.
We want (with the help of the existing XAF Security permissions system) to be able to assign special types of permissions to a role. We can then use these permissions to control the transition to certain states. The State Machine module uses XpoStateMachine and XpoState persistent classes. These classes can be linked to a permission by name. As a result a permission having 2 properties StateMachineName and StateName would be sufficient.
[NonPersistent]
public class StateMachineTransitionPermission : PermissionBase {
public override IPermission Copy() {
return new StateMachineTransitionPermission(Modifier, StateCaption, StateMachineName);
}
public StateMachineTransitionPermission() {
}
public override SecurityElement ToXml() {
SecurityElement result = base.ToXml();
result.AddAttribute("modifier", Modifier.ToString());
result.AddAttribute("stateMachineName", StateMachineName);
result.AddAttribute("stateCaption", StateCaption);
return result;
}
public override void FromXml(SecurityElement e) {
base.FromXml(e);
Modifier =
(StateMachineTransitionModifier)
Enum.Parse(typeof(StateMachineTransitionModifier), e.Attributes["modifier"].ToString());
StateCaption = e.Attributes["stateCaption"].ToString();
StateMachineName = e.Attributes["stateMachineName"].ToString();
}
public StateMachineTransitionPermission(StateMachineTransitionModifier modifier, string stateCaption, string stateMachineName) {
Modifier = modifier;
StateCaption = stateCaption;
StateMachineName = stateMachineName;
}
public override bool IsSubsetOf(IPermission target) {
var isSubsetOf = base.IsSubsetOf(target);
if (isSubsetOf) {
var stateMachineTransitionPermission = ((StateMachineTransitionPermission)target);
return stateMachineTransitionPermission.StateCaption == StateCaption &&
stateMachineTransitionPermission.StateMachineName == StateMachineName;
}
return false;
}
public StateMachineTransitionModifier Modifier { get; set; }
public string StateMachineName { get; set; }
public string StateCaption { get; set; }
}
A Modifier property can be used to disable our permission, moreover the SecuritySystem is going to grant the permission by calling the IsSubsetOf method.
Finally, we are going to create a controller and check if a permission with the same state and statemachine name has been granted to our system. If not we are going to throw an
exception
public class StatePermissionController : ViewController, IModelExtender {
void IModelExtender.ExtendModelInterfaces(ModelInterfaceExtenders extenders) {
extenders.Add<IModelOptions, IModelOptionsStateMachine>();
}
protected override void OnActivated() {
base.OnActivated();
var stateMachineController = Frame.GetController<StateMachineController>();
stateMachineController.TransitionExecuting += OnTransitionExecuting;
}
void OnTransitionExecuting(object sender, ExecuteTransitionEventArgs executeTransitionEventArgs) {
var states = executeTransitionEventArgs.StateMachine.States.OfType<XpoState>();
foreach (var state in states) {
if (IsNotGranted(state))
throw new UserFriendlyException("Permissions are not granted for transitioning to the " + state.Caption);
}
}
bool IsNotGranted(XpoState state) {
return IsNotGranted(new StateMachineTransitionPermission(StateMachineTransitionModifier.Deny, state.Caption, state.StateMachine.Name));
}
static bool IsNotGranted(IPermission permission) {
var securityComplex = ((SecurityBase)SecuritySystem.Instance);
bool isGrantedForNonExistentPermission = securityComplex.IsGrantedForNonExistentPermission;
securityComplex.IsGrantedForNonExistentPermission = true;
bool granted = SecuritySystem.IsGranted(permission);
securityComplex.IsGrantedForNonExistentPermission = isGrantedForNonExistentPermission;
return granted;
}
}
During the writing of this post M. Brekhof asked if it is possible to hide the transition in the UI if there are no permissions. This is a certainly a useful feature to include in the new module. To implement it we can subscribe to the ItemsChanged event of the ChangeStateAction and use the IsGranted method there.
Using the model to control the above allows us more flexibility as we can choose whether to include these improvements or not. In order to do so we need to define and register a model extender.
It should be clear that this is a rapid development! In a few short minutes we have created a module which can be used as often as necessary to enhance the functionality of our applications. This is another fine example of getting the job done the XAF way!
So far we have not discussed how to create lookups for our StateMachineTransitionPermission StateMachineName,StateName properties. Don’t worry all of this will be featured in part 2. In the meantime if any of you need any other information please let me know so that I can cover it too.
Happy eXpanding!
eXpand is the first open source project based on the DevExpress eXpressApp Framework (XAF). More info is available at www.expandframework.com
-
Prerequisites
Manually starting workflows
In the first post of the series we saw how to start a workflow using a WCF service. Furthermore we also discussed doing this using the module’s out of the box mechanisms. So far however, we haven’t had time to analyze the reasons for choosing one method or the other. This post aims to clarify the situation.
WCF Solution
As Dennis likes to say, “There is no need to light a cigar with a nuclear reactor”. This is certainly true when it comes to the WCF solution as it can be somewhat unwieldy. In addition we have to come to terms with more technology as it requires configuration for even the smallest task. For example, the client always needs to know the WCF service address. It is also very difficult to work with WF instances because in order to accomplish common tasks (view, track status, generate reports, measure client service reply time) we need to introduce a system of persistent classes which will help to simulate the out of the box behavior. A third issue arises when modifying the solution because there is often a need for changes to occur in many places at the same time. For example when introducing additional properties we have to change client code and Receive contracts.
This option is only recommended when we have a large system (>10000 WF instances). Only then will we notice a gain in performance. This is because one WCF request can start a workflow which costs nothing compared to multiple Sql Queries. In all other cases we are fortunate that XAF allows us to take the easy road as usual!
Out of the box
Take our usual product ordering task; a client simply creates a new OrderRequest business object and fills the necessary members. A workflow with an AutoStartWhenObjectIsCreated condition will start when the object is saved. After that we can access all the information in the workflow algorithm. This method allows us to,
Note that a similar process is described in Working with CRUD activities – Short Transactions
We would appreciate your feedback on this post. Has it been useful to you? Feel free to contact us with any further questions
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