The IDbConnection and ICloneable Interfaces Providing the ability to set connection and session information for a particular data source is vital to creating a comprehensive data provider. By implementing the IDbConnection interface, a .NET managed data provider can represent a unique session with a data source. Like the IDbCommand interface, some classes that implement the IDbConnection interface may define additional members that add provider-specific functionality. For example, the SqlConnection class defines the PacketSize property in addition to all the other inherited methods. When designing the class that implements the IDbConnection interface, it is important to keep in mind that the Data Access Application Block needs for this class to also implement the ICloneable interface for dynamic discovery of parameters to work. In the base DbCommandWrapper's DoDiscoverParameters method, the ICloneable's Clone method is used to make another copy of the IDbConnection to use for querying for the metadata in the data source. Although there's no reason to discover parameters for reading or writing to XML files, I have still implemented the ICloneable interface to be consistent for what you might need to do if you are creating your own .NET managed data provider. Listing B.5 illustrates how the XmlFileConnection class implements both the IDbConnection and ICloneable interfaces. Listing B.5. XmlFileConnection Implements IDbConnection and ICloneable [C#] public class XmlFileConnection : IDbConnection, ICloneable { private string origConnString; private string fileName; private StringCollection parameters; private ConnectionState state = ConnectionState.Closed; private int connectionTimeout = 0; public XmlFileConnection() { } public XmlFileConnection(string strConnectionString) { ConnectionString = strConnectionString; } public IDbTransaction BeginTransaction(IsolationLevel iso) { return new XmlFileTransaction(this,iso); } public IDbTransaction BeginTransaction() { return new XmlFileTransaction(this); } public void ChangeDatabase(string newdb) { if (! newdb.Equals(fileName)) fileName = newdb; return; } public void Close() { state = ConnectionState.Closed; return; } public IDbCommand CreateCommand() { IDbCommand idbCommand = (IDbCommand)(new XmlFileCommand()); idbCommand.Connection = this; return idbCommand; } public void Open() { state = ConnectionState.Open; } public string ConnectionString { get { return origConnString; } set { origConnString = value; fileName = String.Empty; if (parameters == null) parameters = new StringCollection(); parameters.Clear(); string[] arrConnString = System.Text.RegularExpressions.Regex.Split (value,";,"); foreach (string strParam in arrConnString) { if (fileName.Equals(String.Empty)) fileName = strParam; else parameters.Add(strParam); } } } public int ConnectionTimeout { get { return connectionTimeout; } } public string Database { get { return fileName; } } public ConnectionState State { get { return state; } } public void Dispose() {} public object Clone() { return new XmlFileConnection(ConnectionString); } } [Visual Basic] Public Class XmlFileConnection : Implements IDbConnection, ICloneable Private origConnString As String Private fileName As String Private parameters As StringCollection Private state_Renamed As ConnectionState = ConnectionState.Closed Private connectionTimeout_Renamed As Integer = 0 Public Sub New() End Sub Public Sub New(ByVal strConnectionString As String) ConnectionString = strConnectionString End Sub Public Function BeginTransaction(ByVal iso As IsolationLevel) _ As IDbTransaction Implements IDbConnection.BeginTransaction Return New XmlFileTransaction(Me,iso) End Function Public Function BeginTransaction() As IDbTransaction _ Implements IDbConnection.BeginTransaction Return New XmlFileTransaction(Me) End Function Public Sub ChangeDatabase(ByVal newdb As String) _ Implements IDbConnection.ChangeDatabase If (Not newdb.Equals(fileName)) Then fileName = newdb End If Return End Sub Public Sub Close() Implements IDbConnection.Close state_Renamed = ConnectionState.Closed Return End Sub Public Function CreateCommand() As IDbCommand _ Implements IDbConnection.CreateCommand Dim idbCommand As IDbCommand = _ CType(New XmlFileCommand(), IDbCommand) idbCommand.Connection = Me Return idbCommand End Function Public Sub Open() Implements IDbConnection.Open state_Renamed = ConnectionState.Open End Sub Public Property ConnectionString() As String _ Implements IDbConnection.ConnectionString Get Return origConnString End Get Set origConnString = Value fileName = String.Empty If parameters Is Nothing Then parameters = New StringCollection() End If parameters.Clear() Dim arrConnString As String() = _ System.Text.RegularExpressions.Regex.Split _ (Value,";,") For Each strParam As String In arrConnString If fileName.Equals(String.Empty) Then fileName = strParam Else parameters.Add(strParam) End If Next strParam End Set End Property Public ReadOnly Property ConnectionTimeout() As Integer _ Implements IDbConnection.ConnectionTimeout Get Return connectionTimeout_Renamed End Get End Property Public ReadOnly Property Database() As String _ Implements IDbConnection.Database Get Return fileName End Get End Property Public ReadOnly Property State() As ConnectionState _ Implements IDbConnection.State Get Return state_Renamed End Get End Property Public Sub Dispose() End Sub Public Function Clone() As Object Implements ICloneable.Clone Return New XmlFileConnection(ConnectionString) End Function End Class
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