Provides for immediate loading and filtering of related data.
System.Data.Linq.DataLoadOptions
Namespace: System.Data.Linq
Assembly: System.Data.Linq (in System.Data.Linq.dll)
Public NotInheritable Class DataLoadOptions
public sealed class DataLoadOptions
public ref class DataLoadOptions sealed
[<Sealed>] type DataLoadOptions = class end
The DataLoadOptions type exposes the following members.
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DataLoadOptions | Initializes a new instance of the DataLoadOptions class. |
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AssociateWith(LambdaExpression) | Filters the objects retrieved for a particular relationship. |
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AssociateWith<T>(Expression<Func<T, Object>>) | Filters objects retrieved for a particular relationship. |
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Equals(Object) | Determines whether the specified Object is equal to the current Object. (Inherited from Object.) |
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Finalize | Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.) |
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GetHashCode | Serves as a hash function for a particular type. (Inherited from Object.) |
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GetType | Gets the Type of the current instance. (Inherited from Object.) |
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LoadWith(LambdaExpression) | Retrieves specified data related to the main target by using a lambda expression. |
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LoadWith<T>(Expression<Func<T, Object>>) | Specifies which sub-objects to retrieve when a query is submitted for an object of type T. |
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MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) |
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ToString | Returns a string that represents the current object. (Inherited from Object.) |
General
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.
Rules
Note the following rules regarding DataLoadOptions usage:
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Assigning a DataLoadOptions to a DataContext after the first query has been executed generates an exception.
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Modifying a DataLoadOptions after it has been assigned to a DataContext generates an exception
Cycle Handling
LoadWith and AssociateWith directives must not create cycles. The following represent examples of such graphs:
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Example 1: Self recursive
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dlo.LoadWith<Employee>(e => e.Reports);
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Example 2: Back-pointers
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dlo.LoadWith <Customer>(c => C.Orders);
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dlo.LoadWith <Order>(o => o.Customer);
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Example 3: Longer cycles
Although this should not occur in a well-normalized model, it is possible.
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dlo.LoadWith <A>(a => a.Bs);
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dlo.LoadWith <B>(b => b.Cs);
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dlo.LoadWith <C>(c => c.As);
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Example 4: Self recursive subQueries
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dlo.AssociateWith<A>(a=>a.As.Where(a=>a.Id=33));
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Example 5: Longer recursive subqueries
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dlo.AssociateWith<A>(a=>a.Bs.Where(b=>b.Id==3));
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dlo.AssociateWith<B>(b=>b.As.Where(a=>a.Id==3));
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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.
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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)
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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.
When you retrieve Customers from the Northwind sample database, you can use DataLoadOptions to specify that Orders is also to be retrieved. You can even specify which subset of Orders to retrieve.
.NET Framework
Supported in: 4, 3.5.NET Framework Client Profile
Supported in: 4Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.