EntityDataSource's flattening of complex type properties
I explained a few days ago the rules of wrapping in this blog post. But why do we wrap after all?
In ASP.NET there are different ways of specifying which property a databound control binds to: Eval() Bind(), BoundField.DataField, ListControl.DataTextField, etc. In general, they behave differently.
The flattening we did on EntityDataSource is an attempt to make the properties that are exposed by EDM entities available for 2-way databinding in most of those cases.
For instance, for a customer that has a complex property of type Address, we provide a property descriptor for customer.Address, and also for customer.Address.Street, customer.Address.Number, etc.
At runtime, in the case of a control binding to Eval(“Address.Street”) from a customer, Eval will use the property descriptor corresponding to Address, and it will drill down on it to extract the value of the Street property on it.
A grid column of a BoundField derived type with DataField = “Address.Street” will work differently: it will just look for a property descriptor in the data item with a name as “Address.Street”. In fact, EntityDataSource is the first DataSource control that I know off that will provide such a thing.
Bind(“Address.Street”) will work in a similar fashion to Eval() when reading the properties into the data bound control, but will act a little bit more like BoundField when sending back changes to the DataSource.
There are a few cases in which the behavior is not any of the above and hence you end up with a control that cannot have access to a complex type’s properties. You can expect us to work closely with the ASP.NET team in making the experience smoother in future versions. But for the time being, what you can do is create an explicit projection of the properties. For instance, in Entity SQL:
SELECT c.ContactId, c.Address.Street AS Street
FROM Northwind.Customers AS c
I think it is worthy of mentioning:
- Remember flattening of complex properties only happen under certain conditions (see wrapping).
- We worked very closely with the ASP.NET Dynamic Data in this release, to enable their technology to work EDM through the EntityDataSource. I think it is very worthy of trying.
Hope this helps.