c# qr code library Peeking under the covers of LINQ to SQL in C#.NET

Encoder QR Code in C#.NET Peeking under the covers of LINQ to SQL

Peeking under the covers of LINQ to SQL
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SqlMetal /database:lia.mdf /Namespace:LinqInAction /code:Common.cs /language:csharp /sprocs
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Other times, it may be helpful to generate the metadata first. Do this by directing SqlMetal at your database and sending the results to a file called LiaMetadata.xml as follows:
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SqlMetal /database:lia.mdf /xml:LiaMetadata.xml
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This generated metadata file is an XML file that can be modified to adjust the names of the classes, properties, and columns. Once the metadata is extracted to the XML file, we can use the following command to generate classes based on the metadata rather than going back to the database again:
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SqlMetal /namespace:LinqInAction /code:Common.cs /language:csharp LiaMetadata.xml
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Regardless of how we arrive at our final code, the generated code uses the same basic patterns. Go ahead and run the first SqlMetal command. Open the Common.cs file in Visual Studio and explore the generated code. The file can be broken down into the following sections:
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DataContext
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Partial method declarations for custom logic on insert, update, and delete for each table Overloaded constructors Table accessors Stored procedure and function implementations Change notification event args Private fields Partial method declarations for change notification Constructors Public properties with attribute mapping Properties for associated tables Change notification events
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Partial methods are a new language feature that allows you to insert method stubs that the generated code can optionally call if they are implemented. We ll discuss this more fully in chapter 8.
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Table classes
Classes for object types returned by stored procedures and functions
NOTE
Mapping objects to relational data
The Common.cs file contains a number of class definitions. The first class encapsulates the DataContext that represents the connection to the database. It also includes methods to access each of the tables and other database objects. Following the DataContext class, the generated file includes class definitions for each table in the database. Unlike the simplistic class definitions we ve used thus far, the generated classes have more business functionality. Each class is defined as a partial class. In chapter 8, we ll look at extending this functionality to add custom business logic. The table definitions also contain built-in functionality to manage robust change tracking. When any property s values are changed, the generated code fires change notification events and calls partial methods that will be called if they are implemented. The table classes also offer accessors and tracking of related child objects. Following the table definitions, SqlMetal generates classes to represent the result types for the various stored procedures and functions. These classes are used as the return types of the function declarations established in the custom DataContext class. SqlMetal is great if we want to regenerate our entire database model into a single class file. It can even be included as part of a continuous integration practice by scripting it into a custom MSBuild action. The tool does not give the flexibility to pick and choose which elements will be generated. If there are relationships that aren t included in the database implementation, including table relationships beyond primary key-foreign key relationships that can t be predefined in the database, they won t be scripted as part of the SqlMetal implementation. Also, using SqlMetal to directly generate the entities from the database will be restricted to the names defined in your tables and columns. An intermediary database markup language (DBML) file is required to specify mapping changes as necessary. Perhaps the biggest hindrance for SqlMetal is that it s not a flexible, graphical mapping tool. Visual Studio 2008 comes with a visual designer to help bridge this gap.
The LINQ to SQL Designer
To help developers visually model their data mappings, Visual Studio provides an integrated designer. This designer allows developers to drag and drop objects from their database or manually add conceptual models and visually manage the mappings. Although some expert programmers may shun designers, the tools can often assist not only in seeing a snapshot of the model, but also in helping to learn a new technology. If we re unsure how to map a specific data relationship, we can try using the design tool. We can always go back and tweak the generated code as long as we don t plan on regenerating it.
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