C# Silverlight with Entity Framework - Change Return Type On AutoGenerated EntityQuery?

Question

C# Silverlight with Entity Framework - Change Return Type On AutoGenerated EntityQuery?

c# entity-framework ienumerable silverlight

Question

Background

Currently I have a C# Silverlight business application which uses RIA Services. The application is hosted in ASP.NET using the ADO.NET Entity Framework and a domain service class to read and write to the SQL Server database.

Scenario

I have a server-side method in my DomainServiceClass that returns an IEnumerable list of objects. In my ApplicationName.Web.g.cs file I have an autogenerated function too. In my Silverlight Client Application I want to be able to run a foreach loop over the returned list of objects.

DomainServiceClass Method:

    public IEnumerable<Image> GetJobImages(string jobGuid)
    {
        var query =
            (
             from j in Context.Job
             orderby (j.ShortCode)
             where j.JobID.Equals(jobGuid)
             join a in Context.Audit //.Distinct()
             on j.JobID equals a.Job.JobID
             join i in Context.Image
             on a.Image.JobID equals i.JobID

             select new Image
             {
                 HighResUrl = i.HighResUrl,
                 LowResUrl = i.LowResUrl,
                 UploadDate = i.UploadDate
                 }).AsEnumerable();

        return query;
    }

ApplicationName.Web.g.cs AutoGenerated Function:

    /// <summary>
    /// Returns an EntityQuery for query operation 'GetJobImages'.
    /// </summary>
    public EntityQuery<Image> GetJobImagesQuery(string jobGuid)
    {
        Dictionary<string, object> parameters = new Dictionary<string, object>();
        parameters.Add("jobGuid", jobGuid);
        return base.CreateQuery<Image>("GetJobImages", parameters, false, true);
    }

Silverlight Client Invocation Code:

var context = dds.DomainContext as InmZenDomainContext;
                foreach(var item in context.GetJobImagesQuery(currentJob.JobID.ToString())
                {
                   item.etc.....//
                }

Problem

Unfortunately When I try and invoke this method as above, I receive either the error:

'Cannot implicitly convert type System.Windows.Ria.Data.EntityQuery to System.Collections.IEnumerable'.

OR

'Does not contain a public definition for GetEnumerator'.

After reading and talking to others, I have been informed that I need to change the return type on the AutoGenerated Function (I think).

Question

Does anyone know of a way in which I can change the return type to IEnumerable on this AutoGenerated EntityQuery?! - Or of a different way in which to solve this problem?

Attempted the following:

    /// <summary>
    /// Returns an EntityQuery for query operation 'GetJobImages'.
    /// </summary>
    public IEnumerable<Image> GetJobImagesQuery(string jobGuid)
    {
        Dictionary<string, object> parameters = new Dictionary<string, object>();
        parameters.Add("jobGuid", jobGuid);
        return base.CreateQuery<Image>("GetJobImages", parameters, false, true);
    }

(This fails since the method is autogenerated, it just springs back to what it used to be when I build the solution.)

Help greatly appreciated.

Goober

Popular Answer

You need to load the query and get the results from the load operation. Your Silverlight client invocation code should be modified into something like this:

var context = dds.DomainContext as InmZenDomainContext;
var loadOperation = context.Load(context.GetJobImagesQuery(currentJob.JobID.ToString()));
loadOperation.Completed += (sender, e) => {
  if (!loadOperation.HasError)
    foreach (var item in loadOperation.Entities)
      // Loop over returned items ... Or use LINQ on loadOperation.Entities.
  else
    // loadOperation.Error has details about the error.
    ...
}

Note that all "network calls" are asynchronous in Silverlight.

I would also suggest that you consider changing the query parameter from a string into a GUID.

Martin Liversage

View more on Stack Overflow

Justin Niessner · Accepted Answer · 9/28/2009 1:07:14 PM

The problem is that you're missing a step between your call and the IEnumerable collection.

You need to execute the EntityQuery and use LoadOperation to get your results. It's not as straightforward as you'd think, and here's a good forum post that has an example of how to handle things:

How to get a List<> from LoadOperation

Here's the relevant line from the example:

EntityQuery query = Context.GetEmployeesQuery();

Context.Load<Employee>(query).Completed += (sender, args) => {
    List<Employee> list = ((LoadOperation<Employee>)sender).Entities.ToList();
};

C# Silverlight with Entity Framework - Change Return Type On AutoGenerated EntityQuery?

Question

Background

Scenario

DomainServiceClass Method:

ApplicationName.Web.g.cs AutoGenerated Function:

Silverlight Client Invocation Code:

Problem

Question

Attempted the following:

Fastest Entity Framework Extensions

Accepted Answer

Popular Answer

Performance

Expression Evaluator

Related