Database, Writing In-Memory Data Tables to an XML File

Problem

You have some data in a DataSet object, and you would like to export it to an XML file for later reimportation.

Solution

Use the DataSet's WriteXML() method to send the DataSet content to the file in a common XML format.

Discussion

Recipe 13.8 builds a DataTable object with two state-specific records. The following code adds that table to a DataSet object and writes its records to an XML file:

Dim fullDataSet As New Data.DataSet
 fullDataSet.Tables.Add(stateTable)
 fullDataSet.WriteXml("C:\StateInfo.xml")

Database, Creating In-Memory Data Tables Manually

Problem

You want to manage some data in a database-table-like fashion, but the source data is not coming from a database, or from anything that looks like a table.

Solution

Build a DataTable manually, and fill in all the table details and data yourself.

Discussion

The following code builds a simple table of state information and adds two records:

Dim stateTable As DataTable = New DataTable("UnitedStates")

 ' ----- Use the abbreviation as the primary key.
 Dim priKeyCol(0) As Data.DataColumn
 priKeyCol(0) = stateTable.Columns.Add("ShortName", GetType(String))
 stateTable.PrimaryKey = priKeyCol

 ' ----- Add other data columns.
 stateTable.Columns.Add("FullName", GetType(String))
 stateTable.Columns.Add("Admission", GetType(Date))
 stateTable.Columns.Add("Population", GetType(Long))

Database, Storing the Results of a Query in Memory

Problem

While a data reader is fast and convenient, you would like to keep the retrieved data around for a while, even when you are disconnected from the database or other data source.

Solution

Use the data reader to bring the results into a data set. The DataSet object represents one or more in-memory database tables, each with its records stored in a separate DataTable object.

Discussion

The following code loads all records from the Table1 table into a DataSet object, creating a DataTable object named Table1 within that data set:

' ----- Connect to the database.
 Dim  
connectionString As String = _
    "Data Source=MySystem\SQLEXPRESS;" & _
    "Initial Catalog=MyDatabase;Integrated Security=true"
 Dim theDatabase As New SqlClient.SqlConnection(connectionString)
 theDatabase.Open()

 ' ----- Prepare the SQL statement for use by the data set.
 Dim sqlStatement As New SqlClient.SqlCommand( _
    "SELECT * FROM Table1", theDatabase)

 ' ----- Create the adapter that links the SQL Server-
 '       specific connection and  
command objects with
 '       the database-neutral data set.
 Dim theAdapter As New SqlClient.SqlDataAdapter(sqlStatement)

 ' ----- Create the data set and fill it with the results
 '       of the  
query.
 Dim disconnectedSet As New Data.DataSet
 theAdapter.Fill(disconnectedSet, "Table1")

 ' ----- Clean up.
 theAdapter = Nothing
 sqlStatement = Nothing
 theDatabase.Close()
 theDatabase.Dispose()

Database, Using Stored Procedures

Problem

You need to use a stored procedure in your database, and you're not sure how to specify values for its input and output parameters.

Solution

Use the command object's Parameters collection to set and retrieve stored procedure argument values.

Discussion

Here's a simple SQL Server stored procedure that does nothing more than retrieve a field from a table given its ID value:

CREATE PROCEDURE GetRecordName
    @PriKey int,
    @NameResult varchar(50) OUT
 AS
 BEGIN
    -- Given an ID value, return the RecordName field.
    SET @NameResult =
       (SELECT RecordName FROM Table1 WHERE ID = @PriKey);
 END