实体框架/ RIA服务包括不工作

Question

I've got a SL4 / WCF RIA Services / EF 4 application. I'm having trouble getting my Included entity into my SL4 data context.

In the server side service portion of the application, this is my method:

 [Query(IsDefault = true)]
    public IQueryable<ToolingGroup> GetToolingGroups()
    {
        var groups = this.ObjectContext.ToolingGroups.Include("MetaData").OrderBy(g => g.Name);
        return groups; //breakpoint set here
    }

I assigned it to the var groups to allow it to be inspected before the method returns. If I set a breakpoint before the method returns and add a line to my Watch window the MetaData is there:

groups.First().MetaData

When I let the method return and check it in the silverlight ui completed event MetaData is null.

void loadOperation_Completed(object sender, System.EventArgs e)
    {
        grid.ItemsSource = _toolingContext.ToolingGroups;
        UpdateUI(); //breakpoint set here
    }

When I do this in my watch window MetaData is null:

_toolingContext.ToolingGroups.First().MetaData

I checked to make sure the ToolingGroup returned by the call to .First() in both cases was the same entity and it was.

Why is MetaData lost (eg. null) between the service method and my ui method?

SOLUTION:

// The MetadataTypeAttribute identifies ToolingGroupMetadata as the class
// that carries additional metadata for the ToolingGroup class.
[MetadataTypeAttribute(typeof(ToolingGroup.ToolingGroupMetadata))]
public partial class ToolingGroup
{

    // This class allows you to attach custom attributes to properties
    // of the ToolingGroup class.
    //
    // For example, the following marks the Xyz property as a
    // required property and specifies the format for valid values:
    //    [Required]
    //    [RegularExpression("[A-Z][A-Za-z0-9]*")]
    //    [StringLength(32)]
    //    public string Xyz { get; set; }
    internal sealed class ToolingGroupMetadata
    {

        // Metadata classes are not meant to be instantiated.
        private ToolingGroupMetadata()
        {
        }

        public int Id { get; set; }

        [Include] // Added so MetaData gets serialized
        public MetaData MetaData { get; set; }

        public Nullable<int> MetaDataId { get; set; }

        public string Name { get; set; }

        public ToolingCategory ToolingCategory { get; set; }

        public int ToolingCategoryId { get; set; }

        public EntityCollection<ToolingType> ToolingTypes { get; set; }
    }
}

Answer 1

There are two layers at play here, EF and RIA Services. You've handled the EF part. Now you need to tell RIA services to include that property when it serializes your entities across the wire. In your metadata for the entity, add the [Include] attribute. Like this...

[MetadataType(typeof(ToolingGroup.MetaData)]
public partial class ToolingGroup {
    private class MetaData {

        // adding this attribute tells RIA services 
        // to also send this property across
        [Include]
        public MetaData MetaData { get; set; }
    }
}

It's a bad coincidence that your type is called "Metadata", the ToolingGroup.MetaData class is the metadata that RIA services uses.