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Figure 30-19. The imported stored procedure When we import a stored procedure, a new method is added to the data model context object. This method takes parameters that will be used to execute the procedure. In the case of the Customers By City stored procedure, the method takes a single parameter that is the name of the city we want customer information for. Listing 30-9 demonstrates using the stored procedure in a LINQ query. Listing 30-9. Querying a Stored Procedure using using using using System; System.Collections.Generic; System.Linq; NorthwindModel;
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class Listing 09 { static void Main(string[] args) { // create a context NorthwindEntities context = new NorthwindEntities(); // query the stored procedure IEnumerable<Customers By City Result> results = from e in context.Customers By City("London") where !e.ContactName.Contains("Hardy") select e; foreach (Customers By City Result item in results) { Console.WriteLine("Name: {0}", item.CompanyName); } // wait for input before exiting Console.WriteLine("Press enter to finish"); Console.ReadLine(); } }
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CHAPTER 30 LINQ TO ENTITIES
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As with views, the names of the result types and the name of the context member can be unwieldy, but you can edit the data model and change these if it is a problem. It is a little awkward having to import each stored procedure before it can be used, but once this is done, you can take advantage of the significant performance improvements that stored procedures offer, especially for complex queries. Compiling and running Listing 30-9 produces the following results: Name: Name: Name: Name: Name: Press B's Beverages Consolidated Holdings Eastern Connection North/South Seven Seas Imports enter to finish
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Inserting Data into the Database
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There are four steps to inserting new data into the database using the data model. The first is to create a new instance of one of the entity classes. If we were adding a new row to the Employees table, for example, we would create a new Employee object. Once we have an object, we assign values to its properties that represent the columns of the table we want to insert the record into. At the very least, we have to assign values to those properties that relate to table columns that cannot be null. The third step is to add tell the data model context object that we want to add the object by calling the AddObject method on the appropriate ObjectSet<T> property. The final step is to call the SaveChanges method on the data model context object. This writes our changes to the database. Listing 30-10 demonstrates these steps to create a new row in the Employees table. Listing 30-10. Inserting New Data using using using using System; System.Collections.Generic; System.Linq; NorthwindModel;
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class Listing 10 { static void Main(string[] args) { // create a context NorthwindEntities context = new NorthwindEntities(); // STEP 1 - create the new Employee object Employee myNewEmployee = Employee.CreateEmployee(12345, "Freeman", "Adam"); // STEP 2 - fill in some of the other details of the new object myNewEmployee.City = "London"; myNewEmployee.Country = "UK";
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CHAPTER 30 LINQ TO ENTITIES
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// STEP 3 - add the new object to the context collection for that type context.Employees.AddObject(myNewEmployee); // STEP 4 - save the changes to the database context.SaveChanges(); // wait for input before exiting Console.WriteLine("Press enter to finish"); Console.ReadLine(); } } In Listing 30-10, I have created the new Employee object using the static CreateXXX method that every entity type has. The Employee class has the CreateEmployee method, the Customer class has the CreateCustomer method, and so on. These methods have parameters for the properties that cannot be left null. Using these methods is good practice because it avoids a database error when you inadvertently leave a required field empty. For the Employee entity type, the required fields are for the employee ID and the person s first and last name. If we compile and run Listing 30-10, we can see a new record has been added to the Employees table. We can do this by opening the Database Explorer windows in Visual Studio Express and the Server Explorer in other editions of Visual Studio. Expand the Data Connections item, then the Northwind.mdf item, and then Tables. You will see the list of tables that the database contains, as illustrated by Figure 30-20.
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