Silverlight/xaml - displaying child data in a datagrid

Question

I have two tables in a database and using entity framework and ria services to display data in a simple datagrid. Here is the database/EF structure

Cars      Make
-----     ----
CarId     MakeId
Car       Make
MakeId

In my Silverlight datagrid I want to show the following two columns, for example

Car      Make
---      -----
Escort   Ford
Megane   Renault
Rav4     Toyota

I can easily bind to the Cars table and show cars but I can't work out how to display the Make taken from the child table

The xaml that I am using to configure the datagrid is as follows:

<datagrid:DataGrid x:Name="CarGrid" AutoGenerateColumns="False" MinHeight="100" IsReadOnly="True" ItemsSource="{Binding ElementName=MyData, Path=Data}">
                    <datagrid:DataGrid.Columns>

                        <datagrid:DataGridTextColumn Header="Car" Binding="{Binding Car}"/>
                        <datagrid:DataGridTextColumn Header="Make" Binding="{Binding Cars.Make}"/>
......

The datagrid datasource binds to a DomainDataSource method "GetCars". I'm not sure if it is automatically loading the child table (not sure whether I have to explicitly tell it to or not, and have no idea how to do this in xaml).

I'm sure I could ditch the xaml and do it in c# but I'm trying to be a good coder and do it in xaml.

Answer 1

Unless you specify it explicitly somewhere (using Linq-to-SQL's DataContext.LoadOptions for example), the child record wouldn't be loaded automatically with the parent record.

Here's how it's done in Linq-to-SQL:

List<tblInventory> result;
using (var dc = new SMDataContext())
{
    dc.Log = Console.Out;
    var dlo = new DataLoadOptions();
    dlo.LoadWith<tblInventory>(x => x.tblItemInfo);
    dc.LoadOptions = dlo;
    var q = (from o in dc.tblInventories
             select o).Take(10);
    result = q.ToList();
}

And here's the resulting log:

SELECT TOP 10 [t0].[fldItemPrivateSN], [t0].[fldCatNo], [t0].[fldSerNo], ...
              ..., [t1].[fldWeight], [t1].[fldValue], ...
FROM [dbo].[tblInventory] AS [t0]
INNER JOIN [dbo].[tblItemInfo] AS [t1] ON [t1].[fldCatNo] = [t0].[fldCatNo]
-- Context: SqlProvider(Sql2000) Model: AttributedMetaModel Build: 3.5.30729.1

Update: Also, it appears that you are binding to Cars.Make, try binding to Car.Make instead.

Answer 2

Mike Hilberg's article addresses much of what you are interested in:

http://blogs.msdn.com/mikehillberg/archive/2009/03/26/implementing-selectedvalue-with-the-silverlight-combobox.aspx

as does Manish Dalal's article:

http://weblogs.asp.net/manishdalal/archive/2008/09/28/combobox-in-datagrid.aspx

Even with the help of these examples I struggled to implement the same sort of thing as you (using hand-crafted MVVM rather than RIA).

I ended up with an inelegant hack which did compromise the underlying objects (something you would like to avoid) and that was difficult enough.

Good luck.

Answer 3

You need to change your binding for the Make column to Car.Make, and you need to ensure this Property is being populated by EF.

I'd suggest attaching a debugger to the service and inspecting what is coming out of EF.

You can also attach SQL Profiler to your SQL Server instance and see what query EF is running.