Remarks

A SqlConnection object represents a unique session to a SQL Server data source. With a client/server database system, it is equivalent to a network connection to the server. SqlConnection is used together with SqlDataAdapter and SqlCommand to increase performance when connecting to a Microsoft SQL Server database. For all third-party SQL Server products and other OLE DB-supported data sources, use OleDbConnection .

When you create an instance of SqlConnection , all properties are set to their initial values. For a list of these values, see the SqlConnection constructor.

See ConnectionString for a list of the keywords in a connection string.

If the SqlConnection goes out of scope, it won't be closed. Therefore, you must explicitly close the connection by calling Close or Dispose . Close and Dispose are functionally equivalent. If the connection pooling value Pooling is set to true or yes , the underlying connection is returned back to the connection pool. On the other hand, if Pooling is set to false or no , the underlying connection to the server is actually closed.

Login and logout events will not be raised on the server when a connection is fetched from or returned to the connection pool, because the connection is not actually closed when it is returned to the connection pool. For more information, see SQL Server Connection Pooling (ADO.NET) .

To ensure that connections are always closed, open the connection inside of a using block, as shown in the following code fragment. Doing so ensures that the connection is automatically closed when the code exits the block.

Using connection As New SqlConnection(connectionString)
    connection.Open()
    ' Do work here; connection closed on following line.
End Using
using (SqlConnection connection = new SqlConnection(connectionString))
        connection.Open();
        // Do work here; connection closed on following line.
To deploy high-performance applications, you must use connection pooling. When you use the .NET Framework Data Provider for SQL Server, you do not have to enable connection pooling because the provider manages this automatically, although you can modify some settings. For more information, see SQL Server Connection Pooling (ADO.NET).
If a SqlException is generated by the method executing a SqlCommand, the SqlConnection remains open when the severity level is 19 or less. When the severity level is 20 or greater, the server ordinarily closes the SqlConnection. However, the user can reopen the connection and continue.
An application that creates an instance of the SqlConnection object can require all direct and indirect callers to have sufficient permission to the code by setting declarative or imperative security demands. SqlConnection makes security demands using the SqlClientPermission object. Users can verify that their code has sufficient permissions by using the SqlClientPermissionAttribute object. Users and administrators can also use the Caspol.exe (Code Access Security Policy Tool) to modify security policy at the machine, user, and enterprise levels. For more information, see Security in .NET. For an example demonstrating how to use security demands, see Code Access Security and ADO.NET.
For more information about handling warning and informational messages from the server, see Connection Events. For more information about SQL Server engine errors and error messages, see Database Engine Events and Errors.
Caution
You can force TCP instead of shared memory. You can do that by prefixing tcp: to the server name in the connection string or you can use localhost.
		
Gets a value that indicates whether this DbConnection instance supports the DbBatch class.
		(Inherited from DbConnection)
		
Allows you to set a list of trusted key paths for a database server. If while processing an application query the driver receives a key path that is not on the list, the query will fail. This property provides additional protection against security attacks that involve a compromised SQL Server providing fake key paths, which may lead to leaking key store credentials.
		
When overridden in a derived class, returns a new instance of the provider's class that implements the DbBatch class.
		(Inherited from DbConnection)
		
When overridden in a derived class, creates and returns a DbCommand object associated with the current connection.
		(Inherited from DbConnection)
		
Creates an object that contains all the relevant information required to generate a proxy used to communicate with a remote object.
		(Inherited from MarshalByRefObject)
		
Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.
		(Inherited from DbConnection)
		
Releases the unmanaged resources used by the DbConnection and optionally releases the managed resources.
		(Inherited from DbConnection)
		
Releases the unmanaged resources used by the Component and optionally releases the managed resources.
		(Inherited from Component)
		Obsolete. 
Retrieves the current lifetime service object that controls the lifetime policy for this instance.
		(Inherited from MarshalByRefObject)
		
Returns schema information for the data source of this DbConnection using the specified string for the schema name.
		(Inherited from DbConnection)
		
Returns schema information for the data source of this DbConnection using the specified string for the schema name and the specified string array for the restriction values.
		(Inherited from DbConnection)
		
This is an asynchronous version of GetSchema().
Providers should override with an appropriate implementation.
The cancellationToken can optionally be honored.
The default implementation invokes the synchronous GetSchema() call and returns a completed task.
The default implementation will return a cancelled task if passed an already cancelled cancellationToken.
Exceptions thrown by GetSchema() will be communicated via the returned Task Exception property.
		(Inherited from DbConnection)
		
This is the asynchronous version of GetSchema(String).
Providers should override with an appropriate implementation.
The cancellationToken can optionally be honored.
The default implementation invokes the synchronous GetSchema(String) call and returns a completed task.
The default implementation will return a cancelled task if passed an already cancelled cancellationToken.
Exceptions thrown by GetSchema(String) will be communicated via the returned Task Exception property.
		(Inherited from DbConnection)
		
This is the asynchronous version of GetSchema(String, String[]).
Providers should override with an appropriate implementation.
The cancellationToken can optionally be honored.
The default implementation invokes the synchronous GetSchema(String, String[]) call and returns a completed task.
The default implementation will return a cancelled task if passed an already cancelled cancellationToken.
Exceptions thrown by GetSchema(String, String[]) will be communicated via the returned Task Exception property.
		(Inherited from DbConnection)
		
Returns an object that represents a service provided by the Component or by its Container.
		(Inherited from Component)
		Obsolete. 
Obtains a lifetime service object to control the lifetime policy for this instance.
		(Inherited from MarshalByRefObject)
		
An asynchronous version of Open(), which opens a database connection with the settings specified by the ConnectionString. This method invokes the virtual method OpenAsync(CancellationToken) with CancellationToken.None.
		(Inherited from DbConnection)
		
An asynchronous version of Open(), which opens a database connection with the property settings specified by the ConnectionString. The cancellation token can be used to request that the operation be abandoned before the connection timeout elapses.  Exceptions will be propagated via the returned Task. If the connection timeout time elapses without successfully connecting, the returned Task will be marked as faulted with an Exception. The implementation returns a Task without blocking the calling thread for both pooled and non-pooled connections.
		
This is the asynchronous version of Open(). Providers should override with an appropriate implementation. The cancellation token can optionally be honored.
The default implementation invokes the synchronous Open() call and returns a completed task. The default implementation will return a cancelled task if passed an already cancelled cancellationToken. Exceptions thrown by Open will be communicated via the returned Task Exception property.
Do not invoke other methods and properties of the DbConnection object until the returned Task is complete.
		(Inherited from DbConnection)
		
Returns a String containing the name of the Component, if any. This method should not be overridden.
		(Inherited from Component)