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Walkthrough: Manipulating Data (Visual Basic)

This walkthrough provides a fundamental end-to-end LINQ to SQL scenario for adding, modifying, and deleting data in a database. You will use a copy of the sample Northwind database to add a customer, change the name of a customer, and delete an order.

NoteNote

Your computer might show different names or locations for some of the Visual Studio user interface elements in the following instructions. The Visual Studio edition that you have and the settings that you use determine these elements. For more information, see Customizing Development Settings.

This walkthrough was written by using Visual Basic Development Settings.

This walkthrough requires the following:

  • This walkthrough uses a dedicated folder ("c:\linqtest2") to hold files. Create this folder before you begin the walkthrough.

  • The Northwind sample database.

    If you do not have this database on your development computer, you can download it from the Microsoft download site. For instructions, see Downloading Sample Databases. After you have downloaded the database, copy the northwnd.mdf file to the c:\linqtest2 folder.

  • A Visual Basic code file generated from the Northwind database.

    You can generate this file by using either the Object Relational Designer or the SQLMetal tool. This walkthrough was written by using the SQLMetal tool with the following command line:

    sqlmetal /code:"c:\linqtest2\northwind.vb" /language:vb "C:\linqtest2\northwnd.mdf" /pluralize

    For more information, see SqlMetal.exe (Code Generation Tool).

This walkthrough consists of six main tasks:

  • Creating the LINQ to SQL solution in Visual Studio.

  • Adding the database code file to the project.

  • Creating a new customer object.

  • Modifying the contact name of a customer.

  • Deleting an order.

  • Submitting these changes to the Northwind database.

In this first task, you create a Visual Studio solution that contains the necessary references to build and run a LINQ to SQL project.

To create a LINQ to SQL solution

  1. On the Visual Studio File menu, click New Project.

  2. In the Project types pane in the New Project dialog box, click Visual Basic.

  3. In the Templates pane, click Console Application.

  4. In the Name box, type LinqDataManipulationApp.

  5. Click OK.

This walkthrough uses assemblies that might not be installed by default in your project. If System.Data.Linq is not listed as a reference in your project (click Show All Files in Solution Explorer and expand the References node), add it, as explained in the following steps.

To add System.Data.Linq

  1. In Solution Explorer, right-click References, and then click Add Reference.

  2. In the Add Reference dialog box, click .NET, click the System.Data.Linq assembly, and then click OK.

    The assembly is added to the project.

  3. In the code editor, add the following directives above Module1:

    Imports System.Data.Linq
    Imports System.Data.Linq.Mapping
    

These steps assume that you have used the SQLMetal tool to generate a code file from the Northwind sample database. For more information, see the Prerequisites section earlier in this walkthrough.

To add the northwind code file to the project

  1. On the Project menu, click Add Existing Item.

  2. In the Add Existing Item dialog box, navigate to c:\linqtest2\northwind.vb, and then click Add.

    The northwind.vb file is added to the project.

First, test your connection to the database. Note especially that the name of the database, Northwnd, has no i character. If you generate errors in the next steps, review the northwind.vb file to determine how the Northwind partial class is spelled.

To set up and test the database connection

  1. Type or paste the following code into Sub Main:

    ' Use a connection string, but connect to 
    '     the temporary copy of the database. 
    Dim db As New Northwnd _
        ("C:\linqtest2\northwnd.mdf")
    
    ' Keep the console window open after activity stops.
    Console.ReadLine()
    
  2. Press F5 to test the application at this point.

    A Console window opens.

    Close the application by pressing Enter in the Console window, or by clicking Stop Debugging on the Visual Studio Debug menu.

Creating a new entity is straightforward. You can create objects (such as Customer) by using the New keyword.

In this and the following sections, you are making changes only to the local cache. No changes are sent to the database until you call SubmitChanges toward the end of this walkthrough.

To add a new Customer entity object

  1. Create a new Customer by adding the following code before Console.ReadLine in Sub Main:

    ' Create the new Customer object. 
    Dim newCust As New Customer()
    newCust.CompanyName = "AdventureWorks Cafe"
    newCust.CustomerID = "A3VCA" 
    
    ' Add the customer to the Customers table.
    db.Customers.InsertOnSubmit(newCust)
    
    Console.WriteLine("Customers matching CA before insert:")
    
    Dim custQuery = _
        From cust In db.Customers _
        Where cust.CustomerID.Contains("CA") _
        Select cust
    
    For Each cust In custQuery
        Console.WriteLine("Customer ID: " & cust.CustomerID)
    Next
    
  2. Press F5 to debug the solution.

    The results that are shown in the console window are as follows:

    Customers matching CA before insert:

    Customer ID: CACTU

    Customer ID: RICAR

    Note that the new row does not appear in the results. The new data has not yet been submitted to the database.

  3. Press Enter in the Console window to stop debugging.

In the following steps, you will retrieve a Customer object and modify one of its properties.

To change the name of a Customer

  • Add the following code above Console.ReadLine():

    Dim existingCust = _
        (From cust In db.Customers _
        Where cust.CustomerID = "ALFKI" _
        Select cust).First()
    
    ' Change the contact name of the customer.
    existingCust.ContactName = "New Contact"
    

Using the same customer object, you can delete the first order.

The following code demonstrates how to sever relationships between rows, and how to delete a row from the database.

To delete a row

  • Add the following code just above Console.ReadLine():

    ' Access the first element in the Orders collection. 
    Dim ord0 As Order = existingCust.Orders(0)
    
    ' Access the first element in the OrderDetails collection. 
    Dim detail0 As OrderDetail = ord0.OrderDetails(0)
    
    ' Display the order to be deleted.
    Console.WriteLine _
        (vbCrLf & "The Order Detail to be deleted is: OrderID = " _
        & detail0.OrderID)
    
    ' Mark the Order Detail row for deletion from the database.
    db.OrderDetails.DeleteOnSubmit(detail0)
    

The final step required for creating, updating, and deleting objects is to actually submit the changes to the database. Without this step, your changes are only local and will not appear in query results.

To submit changes to the database

  1. Insert the following code just above Console.ReadLine:

    db.SubmitChanges()
    
  2. Insert the following code (after SubmitChanges) to show the before and after effects of submitting the changes:

    Console.WriteLine(vbCrLf & "Customers matching CA after update:")
    Dim finalQuery = _
        From cust In db.Customers _
        Where cust.CustomerID.Contains("CA") _
        Select cust
    
    For Each cust In finalQuery
        Console.WriteLine("Customer ID: " & cust.CustomerID)
    Next
    
  3. Press F5 to debug the solution.

    The console window appears as follows:

    Customers matching CA before update:
    Customer ID: CACTU
    Customer ID: RICAR
    
    The Order Detail to be deleted is: OrderID = 10643
    
    Customers matching CA after update:
    Customer ID: A3VCA
    Customer ID: CACTU
    Customer ID: RICAR
    
  4. Press Enter in the Console window to stop debugging.

Note Note

After you have added the new customer by submitting the changes, you cannot execute this solution again as is, because you cannot add the same customer again as is. To execute the solution again, change the value of the customer ID to be added.

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