Represents an open connection to a SQL Server database. This class cannot be inherited.
Assembly: System.Data (in System.Data.dll)
Thetype exposes the following members.
|CanRaiseEvents||Gets a value indicating whether the component can raise an event. (Inherited from Component.)|
|ConnectionString||Gets or sets the string used to open a SQL Server database. (Overrides DbConnection.ConnectionString.)|
|ConnectionTimeout||Gets the time to wait while trying to establish a connection before terminating the attempt and generating an error. (Overrides DbConnection.ConnectionTimeout.)|
|Container||Gets the IContainer that contains the Component. (Inherited from Component.)|
|Database||Gets the name of the current database or the database to be used after a connection is opened. (Overrides DbConnection.Database.)|
|DataSource||Gets the name of the instance of SQL Server to which to connect. (Overrides DbConnection.DataSource.)|
|DbProviderFactory||Gets the DbProviderFactory for this DbConnection. (Inherited from DbConnection.)|
|DesignMode||Gets a value that indicates whether the Component is currently in design mode. (Inherited from Component.)|
|Events||Gets the list of event handlers that are attached to this Component. (Inherited from Component.)|
|FireInfoMessageEventOnUserErrors||Gets or sets the FireInfoMessageEventOnUserErrors property.|
|PacketSize||Gets the size (in bytes) of network packets used to communicate with an instance of SQL Server.|
|ServerVersion||Gets a string that contains the version of the instance of SQL Server to which the client is connected. (Overrides DbConnection.ServerVersion.)|
|Site||Gets or sets the ISite of the Component. (Inherited from Component.)|
|State||Indicates the state of the when the most recent network operation was performed on the connection. (Overrides DbConnection.State.)|
|StatisticsEnabled||When set to true, enables statistics gathering for the current connection.|
|WorkstationId||Gets a string that identifies the database client.|
|BeginDbTransaction||Starts a database transaction. (Inherited from DbConnection.)|
|BeginTransaction||Starts a database transaction.|
|BeginTransaction(IsolationLevel)||Starts a database transaction with the specified isolation level.|
|BeginTransaction(String)||Starts a database transaction with the specified transaction name.|
|BeginTransaction(IsolationLevel, String)||Starts a database transaction with the specified isolation level and transaction name.|
|ChangeDatabase||Changes the current database for an open . (Overrides DbConnection.ChangeDatabase(String).)|
|ChangePassword||Changes the SQL Server password for the user indicated in the connection string to the supplied new password.|
|ClearAllPools||Empties the connection pool.|
|ClearPool||Empties the connection pool associated with the specified connection.|
|Close||Closes the connection to the database. This is the preferred method of closing any open connection. (Overrides DbConnection.Close.)|
|CreateCommand||Creates and returns a SqlCommand object associated with the .|
|CreateDbCommand||Creates and returns a DbCommand object associated with the current connection. (Inherited from DbConnection.)|
|CreateObjRef||Creates an object that contains all the relevant information required to generate a proxy used to communicate with a remote object. (Inherited from MarshalByRefObject.)|
|Dispose||Releases all resources used by the Component. (Inherited from Component.)|
|Dispose(Boolean)||Releases the unmanaged resources used by the Component and optionally releases the managed resources. (Inherited from Component.)|
|EnlistDistributedTransaction||Enlists in the specified transaction as a distributed transaction.|
|EnlistTransaction||Enlists in the specified transaction as a distributed transaction. (Overrides DbConnection.EnlistTransaction(Transaction).)|
|Equals(Object)||Determines whether the specified Object is equal to the current Object. (Inherited from Object.)|
|Finalize||Releases unmanaged resources and performs other cleanup operations before the Component is reclaimed by garbage collection. (Inherited from Component.)|
|GetHashCode||Serves as a hash function for a particular type. (Inherited from Object.)|
|GetLifetimeService||Retrieves the current lifetime service object that controls the lifetime policy for this instance. (Inherited from MarshalByRefObject.)|
|GetSchema||Returns schema information for the data source of this . (Overrides DbConnection.GetSchema.)|
|GetSchema(String)||Returns schema information for the data source of this using the specified string for the schema name. (Overrides DbConnection.GetSchema(String).)|
|GetSchema(String, String())||Returns schema information for the data source of this using the specified string for the schema name and the specified string array for the restriction values. (Overrides DbConnection.GetSchema(String, String()).)|
|GetService||Returns an object that represents a service provided by the Component or by its Container. (Inherited from Component.)|
|GetType||Gets the Type of the current instance. (Inherited from Object.)|
|InitializeLifetimeService||Obtains a lifetime service object to control the lifetime policy for this instance. (Inherited from MarshalByRefObject.)|
|MemberwiseClone||Creates a shallow copy of the current Object. (Inherited from Object.)|
|MemberwiseClone(Boolean)||Creates a shallow copy of the current MarshalByRefObject object. (Inherited from MarshalByRefObject.)|
|OnStateChange||Raises the StateChange event. (Inherited from DbConnection.)|
|Open||Opens a database connection with the property settings specified by the ConnectionString. (Overrides DbConnection.Open.)|
|ResetStatistics||If statistics gathering is enabled, all values are reset to zero.|
|RetrieveStatistics||Returns a name value pair collection of statistics at the point in time the method is called.|
|ToString||Returns a String containing the name of the Component, if any. This method should not be overridden. (Inherited from Component.)|
|ICloneable.Clone||Creates a new object that is a copy of the current instance.|
|IDbConnection.BeginTransaction||Begins a database transaction. (Inherited from DbConnection.)|
|IDbConnection.BeginTransaction(IsolationLevel)||Begins a database transaction with the specified IsolationLevel value. (Inherited from DbConnection.)|
|IDbConnection.CreateCommand||Creates and returns a DbCommand object that is associated with the current connection. (Inherited from DbConnection.)|
A 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. 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 , all properties are set to their initial values. For a list of these values, see the constructor.
See ConnectionString for a list of the keywords in a connection string.
If the 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
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 remains open when the severity level is 19 or less. When the severity level is 20 or greater, the server ordinarily closes the . However, the user can reopen the connection and continue.
An application that creates an instance of the object can require all direct and indirect callers to have sufficient permission to the code by setting declarative or imperative security demands. 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 the .NET Framework. For an example demonstrating how to use security demands, see Code Access Security and ADO.NET.
If you are using Microsoft .NET Framework version 1.0, the FullTrust named permission set is required to connect to SQL Server by using Open. This requirement does not apply if you are using .NET Framework version 1.1 or later. For more information, see Requesting Permissions and Named Permission Sets.
For more information about handling warning and informational messages from the server, see Connection Events (ADO.NET). SQL Server engine errors and error messages are documented in SQL Server Books Online.
ADO.NET 2.0 does not support Asynchronous commands over shared memory for SQL Server 2000 or lower. However, 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.
|How to: Create Connections to SQL Server Databases||Data Access in Visual Studio|
The following example creates a SqlCommand and a . The is opened and set as the Connection for the SqlCommand. The example then calls ExecuteNonQuery. To accomplish this, the ExecuteNonQuery is passed a connection string and a query string that is a Transact-SQL INSERT statement. The connection is closed automatically when the code exits the using block.
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.