Provides for immediate loading and filtering of related data.
Assembly: System.Data.Linq (in System.Data.Linq.dll)
Thetype exposes the following members.
|AssociateWith(LambdaExpression)||Filters the objects retrieved for a particular relationship.|
|AssociateWith(Of T)(Expression(Of Func(Of T, Object)))||Filters objects retrieved for a particular relationship.|
|Equals(Object)||Determines whether the specified Object is equal to the current Object. (Inherited from Object.)|
|Finalize||Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)|
|GetHashCode||Serves as a hash function for a particular type. (Inherited from Object.)|
|GetType||Gets the Type of the current instance. (Inherited from Object.)|
|LoadWith(LambdaExpression)||Retrieves specified data related to the main target by using a lambda expression.|
|LoadWith(Of T)(Expression(Of Func(Of T, Object)))||Specifies which sub-objects to retrieve when a query is submitted for an object of type T.|
|MemberwiseClone||Creates a shallow copy of the current Object. (Inherited from Object.)|
|ToString||Returns a string that represents the current object. (Inherited from Object.)|
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.
The 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 usage:
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
Example 5: Longer recursive subqueries
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.
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