ReadXml Method (XmlReader)
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DataTable.ReadXml Method (XmlReader)

 

Reads XML Schema and Data into the DataTable using the specified XmlReader.

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

Public Function ReadXml (
	reader As XmlReader
) As XmlReadMode

Parameters

reader
Type: System.Xml.XmlReader

The XmlReader that will be used to read the data.

Return Value

Type: System.Data.XmlReadMode

The XmlReadMode used to read the data.

The current DataTable and its descendents are loaded with the data from the file named in the supplied XmlReader. The behavior of this method is identical to that of the ReadXml method, except that in this case, data is loaded only for the current table and its descendants.

The ReadXml method provides a way to read either data only, or both data and schema into a DataTable from an XML document, whereas the ReadXmlSchema method reads only the schema.

Note that the same is true for the WriteXml and WriteXmlSchema methods, respectively. To write XML data, or both schema and data from the DataTable, use the WriteXml method. To write just the schema, use the WriteXmlSchema method.

System_CAPS_noteNote

An InvalidOperationException will be thrown if a column type in the DataRow being read from or written to implements IDynamicMetaObjectProvider and does not implement IXmlSerializable.

If an in-line schema is specified, the in-line schema is used to extend the existing relational structure prior to loading the data. If there are any conflicts (for example, the same column in the same table defined with different data types) an exception is raised.

If no in-line schema is specified, the relational structure is extended through inference, as necessary, according to the structure of the XML document. If the schema cannot be extended through inference in order to expose all data, an exception is raised.

System_CAPS_noteNote

The DataSet does not associate an XML element with its corresponding DataColumn or DataTable when legal XML characters like ("_") are escaped in the serialized XML. The DataSet itself only escapes illegal XML characters in XML element names and hence can only consume the same. When legal characters in XML element name are escaped, the element is ignored while processing.

The following example creates a DataTable containing two columns and ten rows. The example writes the DataTable schema and data to an XmlReader. The example creates a second DataTable and calls the ReadXml method to fill it with schema and data from the XmlReader instance.

Private Sub DemonstrateReadWriteXMLDocumentWithReader()
  Dim table As DataTable = CreateTestTable("XmlDemo")
  PrintValues(table, "Original table")

  ' Write the schema and data to XML in a memory stream.
  Dim xmlStream As New System.IO.MemoryStream()
  table.WriteXml(xmlStream, XmlWriteMode.WriteSchema)

  ' Rewind the memory stream.
  xmlStream.Position = 0

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

  ' Print out values in the table.
  PrintValues(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
  table.Columns.Add(column)

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

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

  table.AcceptChanges()
  Return table
End Function

Private Sub PrintValues(ByVal table As DataTable, _
  ByVal label As String)
  Console.WriteLine(label)
  For Each row As DataRow In table.Rows
    For Each column As DataColumn In table.Columns
      Console.Write("{0}{1}", ControlChars.Tab, row(column))
    Next column
    Console.WriteLine()
  Next row
End Sub

.NET Framework
Available since 2.0
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