Establishing Connections in ADOMD.NET
In ADOMD.NET, you use the AdomdConnection object to open connections with analytical data sources, such as Microsoft SQL Server 2005 Analysis Services (SSAS) databases. When the connection is no longer needed, you should explicitly close the connection.
Opening a Connection
To open a connection in ADOMD.NET, you must first specify a connection string to a valid analytical data source and database. Then, you must explicitly open the connection to that data source.
Specifying a Multidimensional Data Source
To specify an analytical data source and database, you set the ConnectionString property of the AdomdConnection object. The connection string specified for the ConnectionString property is an OLE DB–compliant string. ADOMD.NET uses the specified connection string to determine how to connect to the server.
The ConnectionString property can be set on either an existing AdomdConnection object or during the creation an instance of an AdomdConnection object. The following code demonstrates how to set the ConnectionString property when you create an :Microsoft.AnalysisServices.AdomdClient.AdomdConnection:
Dim advwrksConnection As New AdomdConnection("Data Source=localhost;Catalog=AdventureWorksAS")
System.Diagnostics.Debug.Writeline(advwrksConnection.ConnectionString)
AdomdConnection advwrksConnection = new AdomdConnection("Data Source=localhost;Catalog=AdventureWorksAS");
System.Diagnostics.Debug.Writeline(advwrksConnection.ConnectionString);
Opening a Connection to the Data Source
After you have specified the connection string, you must use the Open method to open the connection. When you open a AdomdConnection object, you can set various levels of security for the connection. The security level that is used for the connection depends on the value of the ProtectionLevel connection string setting. For more information about opening secure connections in ADOMD.NET, see Establishing Secure Connections in ADOMD.NET.
Working with a Connection
Each open connection exists in a session, which provides support for stateful operations. A session can be shared by more than one open connection. Sharing a session enables more than one client to share the same context. For more information, see Working With Connections and Sessions in ADOMD.NET.
You can use an open connection to retrieve metadata, data, and run commands. For more information, see Retrieving Metadata from an Analytical Data Source, Retrieving Data from an Analytical Data Source, and Executing Commands Against an Analytical Data Source.
When the connection is open, you can retrieve data, retrieve metadata, and run commands from within a read-committed transaction, in which shared locks are held while the data is being read to avoid dirty reads. The data can still be changed before the end of the transaction, resulting in non-repeatable reads or phantom data. For more information, see Performing Transactions in ADOMD.NET.
Closing a Connection
We recommended that you explicitly close an AdomdConnection object as soon as you no longer need the connection. To explicitly close the connection, you use the Close and Dispose methods of the AdomdConnection object.
A connection that is not explicitly closed, but is allowed to fall out of scope, may not release server resources quickly enough to enable high-concurrency Analysis Services client applications to efficiently open new connections. Depending on how you created the connection, the session used by the AdomdConnection object can remain active if the connection is not explicitly closed.
For more information about sessions, see Working With Connections and Sessions in ADOMD.NET.
.gif "ms123468.note(de-de,SQL.90).gif") Wichtig: |
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| In the Finalize method of any implemented class, do not call the Close or Dispose methods of an AdomdConnection object, AdomdDataReader object, or any other managed object. In a finalizer, only release unmanaged resources that are directly owned by the implemented class. If the implemented class does not own any unmanaged resources, do not include a Finalize method in the class definition. |