FormView with EntityDataSource and DropDownList gi

The problem: when I try to do an update using an EntityDataSource and a FormView that has an <asp:DropDownList> linking to another table, the page loads fine with the proper setting, but on update I get this error message:

A property named 'Vendor.VendorId' was not found on the entity during an insert, update, or delete operation. Check to ensure that properties specified as binding expressions are available to the data source.

The environment and code: using Visual Studio 2010, Entity Framework 4, ASP.NET web forms, and SQL Server 2008 Express.

I have two tables; a Part table and a Vendor table. The Part table has a VendorId column which links to the Vendor table, and it is allowed to be NULL. It is wrapped by Entity Framework.

The part that works: here's the EntityDataSource:

<asp:EntityDataSource ID="PartEntityDataSource" runat="server" 
    ConnectionString="name=PartDBEntities" 
    DefaultContainerName="PartDBEntities" EnableFlattening="True" 
    EntitySetName="Parts" 
    EntityTypeFilter="Part" Where="it.PartId = @PartId" 
    EnableUpdate="True" EnableInsert="True" Include="Vendor">
    <WhereParameters>
        <asp:QueryStringParameter Type="Int64" DefaultValue="null" Name="PartId" 
            QueryStringField="partid" />
        </WhereParameters>
</asp:EntityDataSource>

(Note: I've tried with EnableFlattening on and off.)

This is linked to by a FormView:

<asp:FormView ID="PartEditorFormView" runat="server"
    DataSourceID="PartEntityDataSource"
    DataKeyNames="PartId">

Note that I am forcing the FormView into Edit mode or Insert mode depending on a query string parameters.

Without the DropDownList, I am able to create and update records in the database.

The part that doesn't work: now for the DropDownList. First there is a new EntityDataSource:

<asp:EntityDataSource ID="VendorEntityDataSource" runat="server"
    ConnectionString="name=PartDBEntities"
    DefaultContainerName="PartDBEntities" EnableFlattening="False"
    EntitySetName="Vendors" />

And then the DropDownList in the EditTemplate, using Converting Null in Template Fields:

<asp:DropDownList ID="EditVendorDDL" runat="server" 
    DataSourceID="VendorEntityDataSource" 
    DataTextField='CompanyName' 
    DataValueField='VendorId'
    AppendDataBoundItems="True"
    SelectedValue='<%# Bind("Vendor.VendorId") %>'>
        <asp:ListItem Selected="True" Value="">(none)</asp:ListItem>
</asp:DropDownList>

As I said above, the initial page displays just fine; the DropDownList has the right entries in it and the correct vendor is set to the correct value. Just clicking on the Update button causes the above error.

Here is the relevant part of the stack trace:

[InvalidOperationException: A property named 'Vendor.VendorId' was not found on the entity during an insert, update, or delete operation.
Check to ensure that properties specified as binding expressions are available to the data source.]
System.Web.UI.WebControls.EntityDataSourceView.ConvertProperties(IDictionary values, PropertyDescriptorCollection propertyDescriptors, ParameterCollection referenceParameters, Dictionary`2 convertedValues) +263
System.Web.UI.WebControls.EntityDataSourceView.ExecuteUpdate(IDictionary keys, IDictionary values, IDictionary oldValues) +256
System.Web.UI.DataSourceView.Update(IDictionary keys, IDictionary values, IDictionary oldValues, DataSourceViewOperationCallback callback) +95

I hope that is enough information!

Shouldn't the selectedvalue though be from the PartEntityDataSource perspective, because the VendorEntityDataSource isn't binding the overall data bound control, you need to use <%# Bind("VendorID") %> instead.

HTH.