WPF DataGrid 绑定到导航属性

Question

I'm using Entity Framework 6 in Visual Studio 2015 to create a WPF app with a DataGrid. It needs to bind to search results that contain Entity Framework navigation properties 3 levels deep: An Employee can have any number of EmployeeStatus , and an EmployeeStatus can have an EmployeeStatusDescription entity. So it looks like this:

Employee > EmployeeStatus > EmployeeStatusDescription

I have the following Include()

var comparison = Expression.Lambda<Func<Employee, bool>>(
    Expression.Equal(
        Expression.Property(paramEmployee, selectedColumnValue),
        Expression.Constant(SearchValue)), 
        paramEmployee).Compile();

var query = (from e in Context.Employees
             .Include("EmployeeStatus.EmployeeStatusDescription")
             .Where(comparison)
             select e); 

I try to bind the EmployeeStatusDescription like this:

<DataGrid ItemsSource="{Binding SearchResults}">
    <!-- other columns here... -->
    <DataGridTextColumn Binding="{Binding 
      EmployeeStatus.EmployeeStatusDescription.description}" Header="Status" />
</DataGrid>

But Status column comes up blank for an Employee that has an EmployeeStatus and an associated navigation property EmployeeStatusDescription .

However, on the database, the following SQL brings back the EmployeeStatusDescription just fine:

select esd.* from employee e
    left join EmployeeStatus es on e.employeeID = es.employeeID
    left join EmployeeStatusDescription esd on 
       es.employeeStatusDescriptionID = esd.employeeStatusDescriptionID
where e.employeeID = '30299'

What am I doing wrong? Thanks for your help.

Update 1 : EmployeeStatus is defined in my Employee model like this, so it's a collection, not just a single value:

public virtual ICollection<EmployeeStatu> EmployeeStatus { get; set; }

Update 2 : Here's the EmployeeStatusDescription class:

public partial class EmployeeStatusDescription
{
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
    public EmployeeStatusDescription()
    {
        this.EmployeeStatus = new HashSet<EmployeeStatu>();
    }

    public int employeeStatusDescriptionID { get; set; }
    public string employeeStatusAbbreviation { get; set; }
    public string description { get; set; }
    public bool isActive { get; set; }
    public System.DateTime createdDate { get; set; }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
    public virtual ICollection<EmployeeStatu> EmployeeStatus { get; set; }
}

Answer 1

If EmployeeStatus is a collection, you won't be able to just say EmployeeStatus.EmployeeStatusDescription.description. .NET doesn't know which one to spit back. You could create an IValueConverter that takes in a collection and returns the first.

Or, you could create a property on your viewmodel that returns the first item from the EmployeeStatus collection

    public EmployeeStatus FirstStatus{
       get { if (EmployeeStatus != null) { return EmployeeStatus.First(); } return null; }
    }

Or you could add a content control that would be bound to all the items in the EmployeeStatus collection and list all of them.

Edit To show all the values inside the datagrid for the employee, you'll need another control to iterate the collection. Inside the column that would show the EmployeeStatus, you'll need to make it a template column and add a control that can do the iteration:

<DataGridTemplateColumn Header="Employee Status">
     <DataGridTemplateColumn.CellTemplate>
           <DataTemplate>
               <ListBox ItemsSource="{Binding Source=EmployeeStatus}">
                   <ListBox.ItemTemplate>
                       <DataTemplate>
                           <TextBlock Text="{Binding EmployeeStatusDescription.description}" />
                      </DataTemplate>
                   </ListBox.ItemTemplate>
                </ListBox>
          </DataTemplate>
      </DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>

Items Control Binding

<DataGridTemplateColumn Header="Employee Status">
         <DataGridTemplateColumn.CellTemplate>
               <DataTemplate>
                    <ItemsControl ItemsSource="{Binding EmployeeStatus}">
                         <ItemsControl.ItemTemplate>
                             <DataTemplate>
                                  <TextBlock Text="{Binding EmployeeStatusDescription.description}" />
                             </DataTemplate>
                         </ItemsControl.ItemTemplate>
                     </ItemsControl>
                <DataTemplate>
           <DataGridTemplateColumn.CellTemplate>
  </DataGridTemplateColumn>