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Code sample: Query multiple models (Silverlight)

Last modified on September 26, 2012 12:27

This code sample shows how to query multiple models from a single EntityManager.


Problem

You have multiple Entity Models that represent different back-end datasources. How do you work with them using a single EntityManager so that they can share the same editing and transaction context? 

Solution

This solution demonstrates how to use an EntityManager to query from two separate models.

There are two models - CoreModel and LeafModel, which can be sourced from two different datasources. In this case, they are both from NorthwindIB, but the code does not know the difference.

By default, DevForce generates a typed EntityManager for each model and it contains properties for the basic queries for that model. However, any EntityManager can query for entities from any model. To do this, create a new EntityQuery<T> of the correct entity type, and then use the .With(EntityManager mgr) operator on the query to execute it:

C#
  var entityManager = new CoreModelEntities();

// Query for entities from the EntityManager's default model
 entityManager.Customers.ExecuteAsync(op => {
    MessageBox.Show("Customers fetched: " + op.Results.Count().ToString());
  });
     
 // Query for entities from a different model
 var query = new EntityQuery<Employee>();
  query.With(entityManager).ExecuteAsync(op => {
    MessageBox.Show("Employees fetched: " + op.Results.Count().ToString());
  });
VB
Dim entityManager = New CoreModelEntities()

' Query for entities from the EntityManager's default model
entityManager.Customers.ExecuteAsync(Sub(op) _
   MessageBox.Show("Customers fetched: " & op.Results.Count().ToString()))

' Query for entities from a different model
Dim query = New EntityQuery(Of Employee)()
  query.With(entityManager).ExecuteAsync(Sub(op) _
    MessageBox.Show("Employees fetched: " & op.Results.Count().ToString()))

You can also easily subclass and create your own typed EntityManager with whatever properties you need. The code generated EntityManager contains no "magic" and you can use it as a template for your own.

To navigate from one model to another, we suggest using a repository pattern in a third assembly to avoid circular references between the models. For example, you would call Repository.GetSalesRep(someCustomer) instead of someCustomer.SalesRep.

Created by DevForce on May 03, 2011 16:57

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