9: Modifying Obje cts with LINQ to SQL in C#.NET

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9: Modifying Obje cts with LINQ to SQL
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Specifying a filter for the LINQ query
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for insert, update, and delete operations
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5 The nal design view step is to con gure the to provide links for editing and deleting, as shown in Figure 917
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Data Binding
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This completes the basic sample Run the application to get results, as shown in Figure 918 Now the entities can be edited or deleted as well
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Overall, takes care of a number of complex tasks and provides a simple design-time data-binding capability At runtime, it , forming LINQ queries from string takes care of creating a
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9: Modifying Obje cts with LINQ to SQL
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properties, and returning the results for consumption by a control such as After the user has made a change, it also handles the postback by instance, calling for entities to be creating a new updated, and handling inserts and deletes as well By taking care of a number of plumbing details, it provides simple building blocks for creating a presentation tier in a web application Thus, LINQ to SQL provides a broad array of options for bridging the objects retrieved from the database and your desired presentation tier technology It supports the presentation tier actions affecting the entity lifecycle, from creation through retrieval, update, and deletion, for both smart client and web applications
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Creating a Database
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LINQ to SQL is designed to allow you to think in terms of your objects That is true whether you are retrieving data from the database or binding the results to a presentation tier control In fact, the same principle even extends to creating a database Because entity classes have attributes describing the structure of the relational database tables and columns, you can use this information to create new instances of your database method on the to conYou can call the struct a new database instance with a structure de ned by your classes This allows you to build an application that automatically installs itself on a customer system It also allows you to build a client application that needs a local database to save its of ine state For these scenarios, is ideal However, the data attributes may not encode everything about an existing database s structure The contents of additional indexes, user-de ned functions, stored procedures, triggers, and check constraints are not reprefunction creates a replica of sented by the attributes The the database using only the information it knows It is not designed to be a substitute for full- edged schema design or DDL creation for a complex production database with tuning needs Yet, for a variety of databases, this is suf cient and very expedient from a productivity standpoint
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Here is an example of how you can create a new database named MyDVDsmdf:
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The object model can be used to create a database using the SQL Server Express 2005 database as follows:
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A complementary API allows you to check an existing database and drop it before creating a new one Here is a modi ed version of the database creation code that rst checks for an existing version of the database and then drops it using : using
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After the call to , the new database exists and can to add objects to accept queries and commands such as the MDF le with normal SQL Server, It is also possible to use using either an MDF le or just a catalog name You need to use the appropriate connection string, which you can nd from the connection properties
9: Modifying Obje cts with LINQ to SQL
in Server Explorer in Visual Studio The information in the connection string is used to de ne the database that will exist, not necessarily one that already exists LINQ to SQL nds the relevant bits of information and uses them to determine what database to create and on what server Of course, you need the appropriate rights granted to you on the database server to do so
Summary
LINQ to SQL implements the LINQ query pattern to retrieve entities from the database Applications require additional support for the retrieved entities beyond the LINQ query pattern LINQ to SQL supports modi cation of entities through create, update, and delete operations It also provides rich capabilities for handling concurrent changes through optimistic concurrency checks, con ict resolution, and transactions In addition to the database operation, entities from other tiers can be processed using attach functionality LINQ to SQL also provides rich features for building a presentation tier quickly Retrieved entities are ready for data binding in both the Windows smart client and ASPNET web forms presentation tiers In addition to data access and presentation, LINQ to SQL covers simple deployment through a runtime capability for creating a database from the object model Together these features make it easier to write database applications in an object model-centric fashion