Returning DataTables in WCF/.NET

Asked 2008-08-15T20:26:01.447

I have a WCF service from which I want to return a DataTable. I know that this is often a highly-debated topic, as far as whether or not returning DataTables is a good practice. Let's put that aside for a moment.

When I create a DataTable from scratch, as below, there are no problems whatsoever. The table is created, populated, and returned to the client, and all is well:

[DataContract]
public DataTable GetTbl()
{
    DataTable tbl = new DataTable("testTbl");
    for(int i=0;i<100;i++)
    {
        tbl.Columns.Add(i);
        tbl.Rows.Add(new string[]{"testValue"});
    }
    return tbl;
}

However, as soon as I go out and hit the database to create the table, as below, I get a CommunicationException "The underlying connection was closed: The connection was closed unexpectedly."

[DataContract]
public DataTable GetTbl()
{
    DataTable tbl = new DataTable("testTbl");
    //Populate table with SQL query

    return tbl;
}

The table is being populated correctly on the server side. It is significantly smaller than the test table that I looped through and returned, and the query is small and fast - there is no issue here with timeouts or large data transfer. The same exact functions and DataContracts/ServiceContracts/BehaviorContracts are being used.

Why would the way that the table is being populated have any bearing on the table returning successfully?

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2 Answers

The best way to diagnose these kinds of WCF errors (the ones that really don't tell you much) is to enable tracing. In your web.config file, add the following:

  <system.diagnostics>
    <sources>
      <source name="System.ServiceModel" 
              switchValue="Information" 
              propagateActivity="true">
        <listeners>
          <add name="ServiceModelTraceListener" 
               type="System.Diagnostics.XmlWriterTraceListener, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" 
               initializeData="wcf-traces.svclog"/>
        </listeners>
      </source>
    </sources>
  </system.diagnostics>

You can then open the resulting file in the SvcTraceViewer.exe utility which comes in the .NET Framework SDK (or with Visual Studio). On my machine, it can be found at %PROGRAMFILES%\Microsoft SDKs\Windows\v6.0A\Bin\SvcTraceViewer.exe.

Just look for an error message (in bold red) and that will tell you specifically what your problem is.

answered 2008-08-23T18:56:50.147

I added the Datable to a data set and returned the table like so...

DataTable result = new DataTable("result");

//linq to populate the table

Dataset ds = new DataSet();
ds.Tables.Add(result);
return ds.Tables[0];

Hope it helps :)

answered 2011-10-24T08:29:51.093

Returning DataTables in WCF/.NET

2 Answers

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