10: Using Stored Procedure s and Database Functions in C#

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10: Using Stored Procedure s and Database Functions
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far, the TVF-mapped method can be composed inside an expression tree that is translated into SQL only when the results are consumed Pressing the Enter key provides the following results As in the previous results, Customer entities beyond the rst one are elided in the following listing:
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Using Scalar-Valued Functions Scalar-valued functions return a single value, such as an integer, string, or Like their table-valued counterparts, scalar-valued functions are also free from side effects; hence, they can be composed into a SQL query Hence, LINQ to SQL also supports scalar-valued functions in LINQ queries Let s add the following scalar-valued function to a copy of the sample Northwind database using the steps described in the previous sections The returns the average price function for the given product category
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Stored Procedure s and Functions for Quer ying
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In the LINQ to SQL designer, drag and drop the newly created function onto the designer surface The designer lists a method with the same name as the database function The property grid shows that the method returns the default mapping for the database type Save the dbml le, and use the generated method in a query as follows:
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This LINQ to SQL query uses the method mapped to the scalar-valued function inside a regular LINQ query It produces the following SQL query and results The scalar-valued function is composed inside the generated SQL query
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10: Using Stored Procedure s and Database Functions
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Stored procedures are often used in databases for create (insert), update, and delete (CUD) operations They may ensure access restrictions or include business logic related to the operations Hence, in certain cases, a developer may have no option but to use the stored procedures provided by a database administrator (DBA) for persisting changes to the database LINQ to SQL supports such stored procedures through a combination of designer and runtime support Stored procedures can be used via a more general-purpose mechanism in LINQ to SQL for overriding CUD operations The mechanism works as class contains a method with a canonical name follows: if the and signature of a CUD operation, that method is considered to override the generation of normal dynamic SQL commands for CUD operations The CUD override methods use convention rather than con guration as follows For the Order entity, the three methods are
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The method bodies can contain arbitrary logic, including a call to a stored procedure for carrying out the corresponding operation During processing, for each CUD operation, the LINQ to SQL runtime checks if there is a corresponding CUD override method for that entity and invokes the method if one is found The code generator used in the designer and SqlMetal provides additional help by pregenerating the method signatures as partial method decclass as follows: larations in the
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The LINQ to SQL designer further simpli es the use of stored procedures in the bodies of such override methods with a dialog for specifying the operation and the stored procedure parameters Let s add the following row to the copy of the sample stored procedure for updating an Northwind database using the steps mentioned in previous sections
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Stored Procedure s for Inserts, Update s, and Delete s
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Next, drag and drop the stored procedure onto the designer surface to method, as shown in Figure 104 obtain the
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An update stored procedure mapped to a method
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10: Using Stored Procedure s and Database Functions
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In the left pane, which contains entity classes, right-click the and select Con gure Behavior, as shown in Figure 105
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class,
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Configuring CUD operation on an entity
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The Con gure Behavior dialog lets you specify a stored procedure for CUD operations and map its parameters, as shown in Figure 106 Select Order from the Class drop-down, Update from the Behavior drop-down, and UpdateOrder from the Customize drop-down The stored procedure parameters and entity properties are matched by name and presented In this case, you don t need to change any parameter mappings, so click OK to complete the generation of an update override method Now all update operations will be routed through the override method and, stored procedure listed earlier Insert and in turn, through the delete operations can be con gured in a similar fashion Note that the override methods are not meant to be called in your code; they are de ned so that the LINQ to SQL runtime can call them at the appropriate point when your code calls
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