When you query for an object, you actually retrieve only the object you requested. The related objects are not automatically fetched at the same time. (For more information, see Querying Across Relationships (LINQ to SQL).)

The DataLoadOptions class provides two methods to achieve immediate loading of specified related data. The LoadWith method allows for immediate loading of data related to the main target. The AssociateWith method allows for filtering related objects.

Note the following rules regarding DataLoadOptions usage:

• Assigning a DataLoadOptions to a DataContext after the first query has been executed generates an exception.

• Modifying a DataLoadOptions after it has been assigned to a DataContext generates an exception

LoadWith and AssociateWith directives must not create cycles. The following represent examples of such graphs:

• Example 1: Self recursive

  • dlo.LoadWith<Employee>(e => e.Reports);

• Example 2: Back-pointers

  • dlo.LoadWith <Customer>(c => C.Orders);

  • dlo.LoadWith <Order>(o => o.Customer);

• Example 3: Longer cycles

  Although this should not occur in a well-normalized model, it is possible.

  • dlo.LoadWith <A>(a => a.Bs);

  • dlo.LoadWith <B>(b => b.Cs);

  • dlo.LoadWith <C>(c => c.As);

• Example 4: Self recursive subQueries

  • dlo.AssociateWith<A>(a=>a.As.Where(a=>a.Id=33));

• Example 5: Longer recursive subqueries

  • dlo.AssociateWith<A>(a=>a.Bs.Where(b=>b.Id==3));

  • dlo.AssociateWith<B>(b=>b.As.Where(a=>a.Id==3));

The following are some general rules that help you understand what occurs in these scenarios.

LoadWith Each call to LoadWith checks whether cycles have been introduced into the graph. If there are, as in Examples 1, 2, and 3, an exception is thrown.

AssociateWith The engine at run time does not apply the existing SubQuery clauses to the relationship inside the expression.

• In Example 4, the Where clause is executed against all A, not just the ones sub-filtered by the SubQuery expression itself (because that would be recursive)

• In Example 5, the first Where clause is applied to all the Bs, even though there are subqueries on B. The second Where clause is applied to all the As even though there are subqueries on A.