DataTable.ReadXmlSchema Method (XmlReader)


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Reads an XML schema into the DataTable using the specified XmlReader.

Namespace:   System.Data
Assembly:  System.Data (in System.Data.dll)

Public Sub ReadXmlSchema (
	reader As XmlReader


Type: System.Xml.XmlReader

The XmlReader used to read the schema information.

Use the ReadXmlSchema method to create the schema for a DataTable. The schema includes table, relation, and constraint definitions.

To write a schema to an XML document, use the WriteXmlSchema method.

The XML schema is interpreted according to the XSD standard.

Data corruption can occur if the msdata:DataType and the xs:type types do not match. No exception will be thrown.

The ReadXmlSchema method is generally invoked before invoking the ReadXml method which is used to fill the DataTable.


The way to create a nested relation using XML schema is to have implicit nested elements. Additionally, the nested relation could be re-wired, to use explicit column names. It is mandatory for elements to be implicitly nested for the corresponding DataTables to participate in a nested relation.

The following console application creates a new DataTable, and writes the schema for that table to a MemoryStream. Then, the example creates a new DataTable and reads its schema from the saved XML schema, using a XmlTextReader (which inherits from XmlReader) as its source.

Private Sub DemonstrateReadWriteXMLSchemaWithReader()
  Dim table As DataTable = CreateTestTable("XmlDemo")
  PrintSchema(table, "Original table")

  ' Write the schema to XML in a memory stream.
  Dim xmlStream As New System.IO.MemoryStream()

  ' Rewind the memory stream.
  xmlStream.Position = 0

  Dim newTable As New DataTable
  Dim reader As New System.Xml.XmlTextReader(xmlStream)

  ' Print out values in the table.
  PrintSchema(newTable, "New Table")
End Sub

Private Function CreateTestTable(ByVal tableName As String) _
      As DataTable
  ' Create a test DataTable with two columns and a few rows.
  Dim table As New DataTable(tableName)
  Dim column As New DataColumn("id", GetType(System.Int32))
  column.AutoIncrement = True

  column = New DataColumn("item", GetType(System.String))

  ' Add ten rows.
  Dim row As DataRow
  For i As Integer = 0 To 9
    row = table.NewRow()
    row("item") = "item " & i
  Next i

  Return table
End Function

Private Sub PrintSchema(ByVal table As DataTable, _
      ByVal label As String)
  ' Display the schema of the supplied DataTable:
  For Each column As DataColumn In table.Columns
    Console.WriteLine("{0}{1}: {2}", ControlChars.Tab, _
      column.ColumnName, column.DataType.Name)
  Next column
End Sub

.NET Framework
Available since 2.0
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