| description | title | ms.date | dev_langs | ms.assetid | ||
|---|---|---|---|---|---|---|
Learn more about: Known Issues and Considerations in LINQ to Entities |
Known Issues and Considerations in LINQ to Entities |
03/30/2017 |
|
acd71129-5ff0-4b4e-b266-c72cc0c53601 |
This section provides information about known issues with LINQ to Entities queries.
Starting with .NET Framework 4.5, LINQ to Entities queries are automatically cached. However, LINQ to Entities queries that apply the Enumerable.Contains operator to in-memory collections are not automatically cached. Also parameterizing in-memory collections in compiled LINQ queries is not allowed.
Projecting columns into an anonymous type will cause ordering information to be lost in some queries that are executed against a SQL Server 2005 database set to a compatibility level of "80". This occurs when a column name in the order-by list matches a column name in the selector, as shown in the following example:
[!code-csharp[DP L2E Conceptual Examples#SBUDT543840](../../../../../../samples/snippets/csharp/VS_Snippets_Data/DP L2E Conceptual Examples/CS/Program.cs#sbudt543840)] [!code-vb[DP L2E Conceptual Examples#SBUDT543840](../../../../../../samples/snippets/visualbasic/VS_Snippets_Data/DP L2E Conceptual Examples/VB/Module1.vb#sbudt543840)]
Specifying an unsigned integer type in a LINQ to Entities query is not supported because the Entity Framework does not support unsigned integers. If you specify an unsigned integer, an xref:System.ArgumentException exception will be thrown during the query expression translation, as shown in the following example. This example queries for an order with ID 48000.
[!code-csharp[DP L2E Conceptual Examples#UIntAsQueryParam](../../../../../../samples/snippets/csharp/VS_Snippets_Data/DP L2E Conceptual Examples/CS/Program.cs#uintasqueryparam)] [!code-vb[DP L2E Conceptual Examples#UIntAsQueryParam](../../../../../../samples/snippets/visualbasic/VS_Snippets_Data/DP L2E Conceptual Examples/VB/Module1.vb#uintasqueryparam)]
In Visual Basic, when a property is mapped to a column of SQL Server bit type with a value of 1 using the CByte function, a xref:System.Data.SqlClient.SqlException is thrown with an "Arithmetic overflow error" message. The following example queries the Product.MakeFlag column in the AdventureWorks sample database and an exception is thrown when the query results are iterated over.
[!code-vb[DP L2E Conceptual Examples#SBUDT544355](../../../../../../samples/snippets/visualbasic/VS_Snippets_Data/DP L2E Conceptual Examples/VB/Module1.vb#sbudt544355)]
Referencing a non-scalar variables, such as an entity, in a query is not supported. When such a query executes, a xref:System.NotSupportedException exception is thrown with a message that states "Unable to create a constant value of type EntityType. Only primitive types ('such as Int32, String, and Guid') are supported in this context."
Note
Referencing a collection of scalar variables is supported.
[!code-csharp[DP L2E Conceptual Examples#SBUDT555877](../../../../../../samples/snippets/csharp/VS_Snippets_Data/DP L2E Conceptual Examples/CS/Program.cs#sbudt555877)] [!code-vb[DP L2E Conceptual Examples#SBUDT555877](../../../../../../samples/snippets/visualbasic/VS_Snippets_Data/DP L2E Conceptual Examples/VB/Module1.vb#sbudt555877)]
With SQL Server 2000, LINQ to Entities queries may fail if they produce nested Transact-SQL queries that are three or more levels deep.
If you define your initial query path to include related objects by using the xref:System.Data.Objects.ObjectQuery%601.Include%2A method on the xref:System.Data.Objects.ObjectQuery%601 and then use LINQ to project the returned objects to an anonymous type, the objects specified in the include method are not included in the query results.
[!code-csharp[DP L2E Conceptual Examples#ProjToAnonType1](../../../../../../samples/snippets/csharp/VS_Snippets_Data/DP L2E Conceptual Examples/CS/Program.cs#projtoanontype1)] [!code-vb[DP L2E Conceptual Examples#ProjToAnonType1](../../../../../../samples/snippets/visualbasic/VS_Snippets_Data/DP L2E Conceptual Examples/VB/Module1.vb#projtoanontype1)]
To get related objects, do not project returned types to an anonymous type.
[!code-csharp[DP L2E Conceptual Examples#ProjToAnonType2](../../../../../../samples/snippets/csharp/VS_Snippets_Data/DP L2E Conceptual Examples/CS/Program.cs#projtoanontype2)] [!code-vb[DP L2E Conceptual Examples#ProjToAnonType2](../../../../../../samples/snippets/visualbasic/VS_Snippets_Data/DP L2E Conceptual Examples/VB/Module1.vb#projtoanontype2)]