<services>
		  <service name="WcfJsonTest.Service1">
			  <endpoint address="" behaviorConfiguration="WcfJsonTest.TestServiceBehavior" binding="webHttpBinding" contract="WcfJsonTest.IService1">
			  </endpoint>
		  </service>
	  </services>

		  <endpointBehaviors>
			  <behavior name="WcfJsonTest.TestServiceBehavior">
				  <webHttp helpEnabled="true"/>
			  </behavior>
		  </endpointBehaviors>

public class NorthwindService : DataService<NorthwindEntities>
{
   public static void InitializeService(IDataServiceConfiguration config)
   {
      config.SetEntitySetAccessRule("Customers", EntitySetRights.All);
    }
}

 [DataContract]
    public class CustomerDetails
    {
        [DataMember]
        public int CustomerID { get; set; }
        [DataMember]
        public string AccountNumber { get; set; }
    }

    [ServiceContract]
    public interface ICustomerService
    {
        [OperationContract, WebGet(
            ResponseFormat = WebMessageFormat.Json,
            RequestFormat=WebMessageFormat.Json,
            UriTemplate="Customers")]
        List<CustomerDetails> GetCustomers();
    }

    public class CustomerService : ICustomerService
    {
        public List<CustomerDetails> GetCustomers()
        {
            using (var dbContext = new AdventureWorksEntities())
            {
                var customers = (from customer in dbContext.Customers
                                where customer.CustomerType== "I"
                                select new CustomerDetails
                                           {
                                               CustomerID=customer.CustomerID,
                                               AccountNumber=customer.AccountNumber
                                           }).Take(5);
                var list = customers.ToList();
                return list;
            }
        }
    }

<?xml version="1.0"?>
<configuration>

  <system.web>
    <compilation debug="true" targetFramework="4.0"><assemblies><add assembly="System.Data.Entity, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" /></assemblies></compilation>
  </system.web>
  <system.serviceModel>
	  
	  <services>
		  <service name="WcfJsonTest.CustomerService">
			  <endpoint address="" behaviorConfiguration="WcfJsonTest.TestServiceBehavior" binding="webHttpBinding" contract="WcfJsonTest.ICustomerService">
			  </endpoint>
		  </service>
	  </services>

	  <behaviors>
		  <endpointBehaviors>
			  <behavior name="WcfJsonTest.TestServiceBehavior">
				  <webHttp helpEnabled="true" />
			  </behavior>
		  </endpointBehaviors>
		  <serviceBehaviors>
        <behavior>		
          <!-- To avoid disclosing metadata information, set the value below to false and remove the metadata endpoint above before deployment -->
          <serviceMetadata httpGetEnabled="true" />
          <!-- To receive exception details in faults for debugging purposes, set the value below to true.  Set to false before deployment to avoid disclosing exception information -->
          <serviceDebug includeExceptionDetailInFaults="true" />
			
        </behavior>
      </serviceBehaviors>

	  </behaviors>
    <serviceHostingEnvironment multipleSiteBindingsEnabled="true"/>
  </system.serviceModel>
 <system.webServer>
    <modules runAllManagedModulesForAllRequests="true" />
  </system.webServer>
  
<connectionStrings><add name="AdventureWorksEntities" connectionString="metadata=res://*/Model1.csdl|res://*/Model1.ssdl|res://*/Model1.msl;provider=System.Data.SqlClient;provider connection string=&quot;Data Source=.;Initial Catalog=AdventureWorks;Integrated Security=True;MultipleActiveResultSets=True&quot;" providerName="System.Data.EntityClient" /></connectionStrings></configuration>