Returning DataTable objects with WCF service

Question

This is a strange problem that I am having with WCF trying to send DataTable in the response. I have the following service contract:

[ServiceContract]
public interface ISapphireDataService {
    [OperationContract]
    DataTable LoadData(string query, DateTime start, DateTime end);

    [OperationContract]
    string LoadDataTest();
}

And the following implementation of the methods (where provider is a class that makes the database call and returns back a DataTable):

public DataTable LoadData(string query, DateTime start, DateTime end) {
    //DataSet temp = new DataSet();
    //temp.Tables.Add(provider.LoadData(query, start, end).Copy());
    //return temp;

    return provider.LoadData(query, start, end).Copy();
}

public string LoadDataTest() {
    return "Hello World!";
}

Now, when I leave it like this, I always get an error when calling the LoadData(...) method:

An error occurred while receiving the HTTP response to http://localhost%3A8731/Design%5FTime%5FAddresses/DataProviderServiceLibrary/SapphireDataService/. This could be due to the service endpoint binding not using the HTTP protocol. This could also be due to an HTTP request context being aborted by the server (possibly due to the service shutting down). See server logs for more details.

This is rather odd because the service is configured to use the wsHttpBinding, which I assume uses HTTP propocol. This error does not occur if I try calling the LoadDataTest() method!

So what I have done was put this table I have gotten from the database into a DataSet object and it worked! No errors or anything of the sort. BUT, the table that was returned in the DataSet was EMPTY. All the fields were Null and no data has been transfered/de-serialized properly, it seems :(

This seems to be a common issue but I am yet to see an answer to this that works. Any ideas?

Answer 1

It isn't the best practice to use datasets/datatables over services. They are bulky. Best to use a collection of dataclasses.

Answer 2

While I admit that sending DataSets and DataTables via services is BAD and I actually have changed it so I am not doing so, the root of the problem lied elsewhere.

For those that absolutely HAVE to use DataTables/DataSets, the error I was getting was because I was trying to send a DbNull object. I guess it is not serializable or there is some other reason it refused to send it.

After manually "converting" DbNull into null (I had to do this to extract data into my own custom DataContract anyways), the error was gone and it worked!