TechNet Express: Wcf Data Service fails selecting more than 8 properties (Columns) 'in select ($select) Query

This problem is caused because the way Microsoft and Oracle handles Empty String. To solve this problem all you need to set "HandleNullStringsAsEmptyStrings = true" of oracle data driver as suggested by Devart team

Problem in detail

If you are developing WCF Data Service using Devart Data Driver and try to select more than 8 columns (properties ) in $select query it throws a null

Stack Trace

<?xml version="1.0" encoding="utf-8" standalone="yes" ?>

<message xml:lang="en-US">An error occurred while processing this request.</message>

<message>Value cannot be null. Parameter name: value</message>

<type>System.ArgumentNullException</type>

<stacktrace>at System.Data.Services.WebUtil.CheckArgumentNull[T](T value, String parameterName) at System.Data.Services.Internal.ProjectedWrapper.set_PropertyNameList(String value) at lambda_method(Closure , Shaper ) at System.Data.Common.Internal.Materialization.Coordinator`1.ReadNextElement(Shaper shaper) at System.Data.Common.Internal.Materialization.Shaper`1.SimpleEnumerator.MoveNext() at System.Data.Services.Internal.ProjectedWrapper.EnumeratorWrapper.MoveNext() at System.Data.Services.DataService`1.SerializeResponseBody(RequestDescription description, IDataService dataService) at System.Data.Services.DataService`1.HandleNonBatchRequest(RequestDescription description) at System.Data.Services.DataService`1.HandleRequest()</stacktrace>

</innererror>

</error>

Solution

Just add one line in the service initialization code.

public static void InitializeService(DataServiceConfiguration config)

{

// ….. Other code

Devart.Data.Oracle.Entity.OracleEntityProviderServices.HandleNullStringsAsEmptyStrings = true;

}

Root Cause

This problem is combination of two issue ,