SqlConnection Class

.NET Framework 4

Represents an open connection to a SQL Server database. This class cannot be inherited.

System.Object
  System.MarshalByRefObject
    System.ComponentModel.Component
      System.Data.Common.DbConnection
        System.Data.SqlClient.SqlConnection

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

Syntax

C++

JScript

'Declaration

Public NotInheritable Class SqlConnection _
	Inherits DbConnection _
	Implements ICloneable

The SqlConnection type exposes the following members.

Constructors

	Name	Description
	SqlConnection	Initializes a new instance of the SqlConnection class.
	SqlConnection(String)	Initializes a new instance of the SqlConnection class when given a string that contains the connection string.

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Properties

	Name	Description
	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 SqlConnection. (Overrides DbConnection.State.)
	StatisticsEnabled	When set to true, enables statistics gathering for the current connection.
	WorkstationId	Gets a string that identifies the database client.

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Methods

	Name	Description
	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 SqlConnection. (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 SqlConnection.
	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 SqlConnection. (Overrides DbConnection.GetSchema.)
	GetSchema(String)	Returns schema information for the data source of this SqlConnection using the specified string for the schema name. (Overrides DbConnection.GetSchema(String).)
	GetSchema(String, String())	Returns schema information for the data source of this SqlConnection 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.)

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Events

	Name	Description
	Disposed	Occurs when the component is disposed by a call to the Dispose method. (Inherited from Component.)
	InfoMessage	Occurs when SQL Server returns a warning or informational message.
	StateChange	Occurs when the state of the event changes. (Inherited from DbConnection.)

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Explicit Interface Implementations

	Name	Description
	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.)

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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.

Note
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.

C++

JScript

Using connection As New SqlConnection(connectionString)
    connection.Open()
    ' Do work here; connection closed on following line.
End Using

Note
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 the .NET Framework. For an example demonstrating how to use security demands, see Code Access Security and ADO.NET.

Note
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.

Caution
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.

Topic	Location
How to: Create Connections to SQL Server Databases	Data Access in Visual Studio
How to: Create Connections to SQL Server Databases	Data Access in Visual Studio

Examples

The following example creates a SqlCommand and a SqlConnection. The SqlConnection 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.

C++

JScript

Public Sub CreateCommand(ByVal queryString As String, _
  ByVal connectionString As String)
    Using connection As New SqlConnection(connectionString)
        Dim command As New SqlCommand(queryString, connection)
        command.Connection.Open()
        command.ExecuteNonQuery()
    End Using
End Sub

Version Information

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Platforms

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role not supported), 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.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.