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Visual Basic 2012 Programmer's Reference by Rod Stephens

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LINQ TO ADO.NET

LINQ to ADO.NET provides tools that let your applications apply LINQ-style queries to objects used by ADO.NET to store and interact with relational data.

LINQ to ADO.NET includes three components: LINQ to SQL, LINQ to Entities, and LINQ to DataSet. The following sections briefly give additional details about these three pieces.

LINQ to SQL and LINQ to Entities

LINQ to SQL and LINQ to Entities are object-relational mapping (O/RM) tools that build strongly typed classes for modeling databases. They generate classes to represent the database and the tables that it contains. LINQ features provided by these classes allow a program to query the database model objects.

For example, to build a database model for use by LINQ to SQL, select the Project menu’s Add New Item command and add a new “LINQ to SQL Classes” item to the project. This opens a designer where you can define the database’s structure.

Now you can drag SQL Server database objects from the Server Explorer to build the database model. If you drag all of the database’s tables onto the designer, you should be able to see all of the tables and their fields, primary keys, relationships, and other structural information.

LINQ to SQL defines a DataContext class to represent the database. Suppose a program defines a DataContext class named dcTestScores and creates an instance of it named db. Then the following code selects all of the records from the Students table ordered by first and last name:

Dim query = From ...

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