Database, Reading an XML File into In-Memory Data Tables

Problem

You previously exported a DataSet to an XML file, and now you need to get it back.

Solution

Use the DataSet object's ReadXML() method to restore data from a previously generated XML export.

Discussion

Recipe 13.9 exports some XML and a related schema for a table with state-specific information. To read it back into a DataSet object, use the following code:

Dim stateSet As New Data.DataSet
 stateSet.ReadXmlSchema("c:\StateSchema.xml")
 stateSet.ReadXml("c:\StateInfo.xml")

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 Transaction

Problem

You need to issue multiple database updates in the context of a single, atomic transaction.

Solution

Use an ADO.NET transaction to envelop the various SQL statements that need to be processed as a unit.

Discussion

The following block of code connects to a database via ADO.NET and makes several database updates within a single transaction:

' ----- 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( )

 ' ----- Create a command object that will hold each
 '       processed SQL statement.
 Dim sqlStatement As New SqlClient.SqlCommand
 sqlStatement.Connection = theDatabase