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Figure 71: Sample Application Schematic Diagram
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classes, and on the utility routines that are used to provide functionality to all objects, and especially on the use of LINQ within that code You can find the complete code for all three versions of the application at the book s website Each version has its own project subdirectory: LinqToDatasets, LinqToObjects, and LinqHybrid The main starting point for the application is the retrieval of the employee s orders from the Northwind database The employee s row must be retrieved from the Employees table, the employee s orders retrieved from the Orders table, and their details retrieved from the Order Details table Since an employee can sell any product to any customer, all rows must be retrieved from both the Customers and the Products tables This information is gathered by a SQL Server stored procedure that takes the employee ID as its only parameter and retrieves the necessary rows from each table Listing 73 shows this procedure
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Listing 73: SQL Server Stored Procedure for Accessing Employee s Order Records
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ALTER PROCEDURE dboprocGetEmployee @EmployeeID int
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72 The Sample Application
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AS BEGIN SET NOCOUNT ON; SELECT * FROM dboEmployees WHERE EmployeeID = @EmployeeID SELECT * FROM dboCustomers SELECT * FROM dboProducts SELECT * FROM dboOrders WHERE EmployeeID = @EmployeeID SELECT * FROM dbo[Order Details] WHERE OrderID IN ( SELECT OrderID FROM dboOrders WHERE EmployeeID = @EmployeeID ) END GO
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The information retrieved by this stored procedure, when brought into the application s memory space, results in the application data structure that is diagrammed in Figure 72 Throughout this chapter, we will refer to this data as the application data, regardless of whether it is stored in data tables within a data set or in collections of business objects contained within a parent XML-serializable object Within the application, the data that was retrieved from the [Order Details] table will be known by the one-word name, Details The authors of this book have strong, and not positive, opinions regarding the use of spaces within object names Now that we have the server-side stored procedure in place, we turn our attention to the client-side application and the code needed to receive and process the data We start with the LINQ to Datasets version Since we ll be using LINQ to Datasets, we can make our schematic diagram a bit more specific, as shown in Figure 73
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Figure 72: The Application s Data
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Figure 73: Sample Application Diagram: LINQ to Datasets
721 LINQ to Datasets As we did in 6, ADONET Programming, we ll use a DataAdapter object to receive the data from the stored procedure and place it in a data
72 The Sample Application
set But this time we have five SELECT statements in our stored procedure Therefore, our adapter will need to generate five tables in our data set and load each with the results from a different SELECT statement Before executing the adapter s Fill method, we will need to tell the adapter what name to give each table in the data set We do not need to tell the adapter what data source tables were used, as the adapter knows each incoming result set within the output of a multi SELECT command by the names Table, Table1, Table2, and so on, regardless of the underlying database table names We match the name that we want the adapter to give each data table to the incoming result sets Table, Table1, Table2, and so on by adding entries to the adapter s TableMappings collection In our case, five entries are required, as shown in the following code snippet:
daptTableMappingsAdd("Table", "Employees"); daptTableMappingsAdd("Table1", "Customers"); daptTableMappingsAdd("Table2", "Products"); daptTableMappingsAdd("Table3", "Orders"); daptTableMappingsAdd("Table4", "Details");
Listing 74 provides the complete code necessary to accomplish the following four tasks 1 2 3 4 Create an empty Dataset Create the connection, command, and adapter objects Set the TableMappings collection Retrieve the data and load it into the data set
The connectionString and employeeID are passed into the function containing the code The resulting DataSet has the structure shown in Figure 74 and is the application data object for this version of the application To make all three versions of our application as consistent as possible, we will always place a reference to the application data object into a static field named AppData located in the Program class In this version, the data set is the application data object The code shown in Listing 74 does not contain any LINQ statements, for it just loads data from a remote database into a data set on the device Only after we have placed the data into the data set will we begin to use LINQ to manipulate that data