Wpf binding error in datagrid still shows value

Question

I have a wpf application (MVVM style) that has a datagrid. I am using entity framework as my model. In this datagrid I have a column that comes from a value in another table. I use navigation properties to get this value. When the datagrid loads the column in question displays the right value, but there is still a binding error being generated in the output window:

System.Windows.Data Error: 40 : BindingExpression path error: 'product_category' property not found on 'object' ''tracking_stock_EA7F46EC8AD7F155921357AA6714C6C20BE807C4760A3B6DFC4FAC1954CA8119' (HashCode=49385318)'. null

The object that the datagrid row is bound to is called a tracking_stock which has a navigation property of product, which itself has a navigation property of products_category which i use to get the product_category.chrProdCtgry

Here is an image to outline the EF design: entity-framework-design

so the binding for my textblock inside a datagrid template column is as follows:

<DataGridTemplateColumn Header="CATEGORY" SortMemberPath="product.product_category.chrProdCtgry" ToolTipService.ToolTip="Category of the product" >
    <DataGridTemplateColumn.CellTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding product.product_category.chrProdCtgry}" Style="{StaticResource FTC_DetailLabelSub}" Width="120" TextWrapping="NoWrap"/>
        </DataTemplate>
    </DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>

Now, everything works, the column can be sorted, the text in the textblock has the value it is supposed to.

QUESTION:

Why is this binding error being thrown when everything works properly?

Edit # 1:

I tried to remove the sort declaration:

SortMemberPath="product.product_category.chrProdCtgry"

The binding error is still there

Edit # 2:

So I tried adding the IsAsync=True to both the textblock and collection binding for the datagrid itself. Now the textblock value does not show up until I sort the category column. In addition the binding errors listed above are still present, but now a new one is generated:

System.Windows.Data Error: 17 : Cannot get 'product_category' value (type 'product_category') from 'product' (type 'product_83A5741ABC5EE6395B89B7B4B384137E8CF95991EF9918BD4525EF06B774469E'). BindingExpression:Path=product.product_category.chrProdCtgry; DataItem='tracking_stock_EA7F46EC8AD7F155921357AA6714C6C20BE807C4760A3B6DFC4FAC1954CA8119' (HashCode=2011918); target element is 'TextBlock' (Name=''); target property is 'Text' (type 'String') TargetInvocationException:'System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.NullReferenceException: Object reference not set to an instance of an object.

Edit #3:

Sherridan's post got me thinking about the data not being there when the datagrid's collection is created from the dataBase context. So I went back to the entity framework "GET" function and forced an include of the navigation properties in the following three ways, none of which got rid of the binding error:

1

Dim trackingList = Await Context.tracking_stock.Include("product").ToListAsync
Return New ObservableCollection(Of tracking_stock)(trackingList)

2

Dim trackingList = Await Context.tracking_stock.Include("product.product_category").ToListAsync
Return New ObservableCollection(Of tracking_stock)(trackingList)

3

Dim trackingList = Await Context.tracking_stock.Include("product").Include("product.product_category").ToListAsync
Return New ObservableCollection(Of tracking_stock)(trackingList)

Sheridan Sheridan · Accepted Answer · 2013-09-04T15:54:35

This can sometimes happen if you are using asynchronous data access operations... this could be an error from before the data arrives and is data bound. I had this problem and I solved it by adding IsAsync="True" to my Binding.

UPDATE >>>

According to the first edit to your question, if you removed the sort declaration and the error was still there, then that was not the cause of your error. Search through your entire solution for product.product_category.chrProdCtgry... there must be another instance of this text used in a binding somewhere. I'm about to go home, but given time, I'll try to take another look at this later.