How to populate a DataSet object from a database by using Visual Basic .NET

For a Microsoft Visual C# .NET version of this article, see
314145 .
For a Microsoft Visual Basic 6.0 version of this article, see
168336 .

This article refers to the following Microsoft .NET Framework Class Library namespaces:
  • System
  • System.Data
  • System.Data.SqlClient

IN THIS TASK

Summary

DataSet objects, a key part of data access in the Microsoft .NET Framework, are in-memory objects that can hold tables, views, and relationships. This article shows how to fill a DataSet object with the results of one or more database queries, and how to access that data after it is loaded into the DataSet object.

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Requirements

The following list outlines the recommended hardware, software, network infrastructure, and service packs that you need:
  • Microsoft Windows 2000 Professional, Windows 2000 Server, Windows 2000 Advanced Server, or Windows NT 4.0 Server
  • Microsoft SQL Server 7.0, SQL Server 2000, or Microsoft Data Engine with the Pubs sample database installed
  • Microsoft Visual Studio .NET
This article assumes that you are familiar with the following topics:
  • Database terminology
  • Structured Query Language (SQL)
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Filling a DataSet

Using a variety of objects from within the System.Data namespace, you can connect to a database server, run a query, and have the results placed into a DataSet object. The DataSet is a disconnected object. Therefore, after the data is loaded, the connection to the database is no longer used until you want to load more data or update the server with the changes you have made to your in-memory copy of the information.

To load data from a database into a DataSet, follow these steps:
  1. Start Visual Studio .NET.
  2. Create a new Console Application project in Microsoft Visual Basic .NET. Visual Studio .NET creates a Module for you, along with an empty Main procedure.
  3. Make sure that the project references the System and System.Data namespaces.
  4. Use the Imports statement on the System, System.Data, and System.Data.SqlClient namespaces so that you are not required to qualify declarations from these namespaces later in your code. You must use these statements before any other declarations.
    Imports System
    Imports System.Data
    Imports System.Data.SqlClient
  5. The first step to get data from the database to the DataSet is to establish a database connection, which requires a System.Data.SqlClient.SqlCommand object and a connection string. The connection string in the code to follow connects a SQL Server server that is located on the local computer (the computer where the code is running). You must modify this connection string as appropriate for your environment. After the SqlConnection object is created, call the Open method of that object to establish the actual database link.
    Dim sConnectionString As String
    sConnectionString = "Password=<strong password>;User ID=<username>;" & _
    "Initial Catalog=pubs;" & _
    "Data Source=(local)"

    Dim objConn As New SqlConnection(sConnectionString)
    objConn.Open()
  6. Create a DataAdapter object, which represents the link between the database and your DataSet object. You can specify SQL or another type of command that is used to retrieve data as part of the constructor object of the DataAdapter. This sample uses a SQL statement that retrieves records from the Authors table in the Pubs database.
    Dim daAuthors As _
    New SqlDataAdapter("Select * From Authors", objConn)
  7. You must declare and create an instance of a DataSet object, at which time you can supply a name for the entire DataSet before you can start to load any data. The name may contain several distinct tables.
    Dim dsPubs As New DataSet("Pubs")
  8. The SqlDataAdapter class provides two methods, Fill and FillSchema, that are crucial to loading this data. Both of these methods load information into a DataSet. Fill loads the data itself, and FillSchema loads all of the available metadata about a particular table (such as column names, primary keys, and constraints). A good way to handle the data loading is to run FillSchema followed by Fill. For example:
    daAuthors.FillSchema(dsPubs, SchemaType.Source, "Authors")
    daAuthors.Fill(dsPubs, "Authors")
    If you only use Fill, you can only load the basic metadata that is required to describe the column names and data types. The Fill method does not load primary key information. To change this default behavior, you can set the MissingSchemaAction property of the DataAdapter object to MissingSchemaAction.AddWithKey, which loads the primary key metadata along with the default information. For example:
    daAuthors.MissingSchemaAction = MissingSchemaAction.AddWithKey
    daAuthors.Fill(dsPubs, "Authors")
  9. The data is now available as an individual DataTable object within the Tables collection of the DataSet. If you specified a table name in the calls to FillSchema and Fill, you can use that name to access the specific table that you want.
    Dim tblAuthors As DataTable
    tblAuthors = dsPubs.Tables("Authors")
  10. You can use a For Each loop to loop through all of the DataRow objects within the Rows collection of a DataTable. This gives you access to each row of the table. You can access columns by name or by positional index (with '0' being the first column position). For example:
    Dim drCurrent As DataRow
    For Each drCurrent In tblAuthors.Rows
    Console.WriteLine("{0} {1}", _
    drCurrent("au_fname").ToString, _
    drCurrent("au_lname").ToString)
    Next
    Console.ReadLine()
  11. Save your project. On the Debug menu, click Start to run your project and make sure that it works.
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Complete code listing

Note: You will need to change User ID <username> and password =<strong password> to the correct values before you run this code. Be sure that User ID has the appropriate permissions to perform this operation on the database.
Option Explicit On 
Option Strict On

Imports System
Imports System.Data
Imports System.Data.SqlClient

Module Module1

Sub Main()
Dim sConnectionString As String
sConnectionString = "Password=<strong password>;User ID=<username>;" & _
"Initial Catalog=pubs;" & _
"Data Source=(local)"

Dim objConn As New SqlConnection(sConnectionString)
objConn.Open()

Dim daAuthors As _
New SqlDataAdapter("Select * From Authors", objConn)

Dim dsPubs As New DataSet("Pubs")
daAuthors.FillSchema(dsPubs, SchemaType.Source, "Authors")
daAuthors.Fill(dsPubs, "Authors")

Dim tblAuthors As DataTable
tblAuthors = dsPubs.Tables("Authors")

Dim drCurrent As DataRow
For Each drCurrent In tblAuthors.Rows
Console.WriteLine("{0} {1}", _
drCurrent("au_fname").ToString, _
drCurrent("au_lname").ToString)
Next
Console.ReadLine()
End Sub

End Module
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References

For more information about ADO.NET, DataSet objects, and SQL, refer to the following Microsoft Web sites:
"Diving into Data Access" (an MSDN Voices column by Dino Esposito)
http://msdn2.microsoft.com/en-us/library/ms810293.aspx

ADO.NET for the ADO Programmer
http://msdn2.microsoft.com/en-us/library/ms973217.aspx

MSDN Online .NET Framework Developer Center
http://msdn2.microsoft.com/en-us/netframework/default.aspx
For more information, see the following topics in the Visual Studio .NET Help documentation or the following Microsoft Web sites:
Walkthrough: Creating a Distributed Application
http://msdn.microsoft.com/en-us/library/1as0t7ff.aspx

Walkthrough: Creating a Master-Detail Windows Form
http://msdn.microsoft.com/en-us/library/aa984462.aspx
If you installed the QuickStart samples, sample projects are available in the following directory:
C:\Program Files\Microsoft.NET\FrameworkSDK\Samples
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Eigenschappen

Artikel-id: 301216 - Laatst bijgewerkt: 27 nov. 2008 - Revisie: 1

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