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SqlConnection Class

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

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

public sealed class SqlConnection : DbConnection, 
	ICloneable

The SqlConnection type exposes the following members.

  NameDescription
Public methodSqlConnection()Initializes a new instance of the SqlConnection class.
Public methodSqlConnection(String)Initializes a new instance of the SqlConnection class when given a string that contains the connection string.
Public methodSqlConnection(String, SqlCredential)Initializes a new instance of the SqlConnection class given a connection string, that does not use Integrated Security = true and a SqlCredential object that contains the user ID and password.
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  NameDescription
Public propertyClientConnectionIdThe connection ID of the most recent connection attempt, regardless of whether the attempt succeeded or failed.
Public propertyConnectionStringGets or sets the string used to open a SQL Server database. (Overrides DbConnection.ConnectionString.)
Public propertyConnectionTimeoutGets the time to wait while trying to establish a connection before terminating the attempt and generating an error. (Overrides DbConnection.ConnectionTimeout.)
Public propertyContainerGets the IContainer that contains the Component. (Inherited from Component.)
Public propertyCredentialGets or sets the SqlCredential object for this connection.
Public propertyDatabaseGets the name of the current database or the database to be used after a connection is opened. (Overrides DbConnection.Database.)
Public propertyDataSourceGets the name of the instance of SQL Server to which to connect. (Overrides DbConnection.DataSource.)
Public propertyFireInfoMessageEventOnUserErrorsGets or sets the FireInfoMessageEventOnUserErrors property.
Public propertyPacketSizeGets the size (in bytes) of network packets used to communicate with an instance of SQL Server.
Public propertyServerVersionGets a string that contains the version of the instance of SQL Server to which the client is connected. (Overrides DbConnection.ServerVersion.)
Public propertySiteGets or sets the ISite of the Component. (Inherited from Component.)
Public propertyStateIndicates the state of the SqlConnection during the most recent network operation performed on the connection. (Overrides DbConnection.State.)
Public propertyStatisticsEnabledWhen set to true, enables statistics gathering for the current connection.
Public propertyWorkstationIdGets a string that identifies the database client.
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  NameDescription
Public methodBeginTransaction()Starts a database transaction.
Public methodBeginTransaction(IsolationLevel)Starts a database transaction with the specified isolation level.
Public methodBeginTransaction(String)Starts a database transaction with the specified transaction name.
Public methodBeginTransaction(IsolationLevel, String)Starts a database transaction with the specified isolation level and transaction name.
Public methodChangeDatabaseChanges the current database for an open SqlConnection. (Overrides DbConnection.ChangeDatabase(String).)
Public methodStatic memberChangePassword(String, String)Changes the SQL Server password for the user indicated in the connection string to the supplied new password.
Public methodStatic memberChangePassword(String, SqlCredential, SecureString)Changes the SQL Server password for the user indicated in the SqlCredential object.
Public methodStatic memberClearAllPoolsEmpties the connection pool.
Public methodStatic memberClearPoolEmpties the connection pool associated with the specified connection.
Public methodCloseCloses the connection to the database. This is the preferred method of closing any open connection. (Overrides DbConnection.Close().)
Public methodCreateCommandCreates and returns a SqlCommand object associated with the SqlConnection.
Public methodCreateObjRefCreates an object that contains all the relevant information required to generate a proxy used to communicate with a remote object. (Inherited from MarshalByRefObject.)
Public methodDispose()Releases all resources used by the Component. (Inherited from Component.)
Public methodEnlistDistributedTransactionEnlists in the specified transaction as a distributed transaction.
Public methodEnlistTransactionEnlists in the specified transaction as a distributed transaction. (Overrides DbConnection.EnlistTransaction(Transaction).)
Public methodEquals(Object)Determines whether the specified object is equal to the current object. (Inherited from Object.)
Public methodGetHashCodeServes as the default hash function. (Inherited from Object.)
Public methodGetLifetimeServiceRetrieves the current lifetime service object that controls the lifetime policy for this instance. (Inherited from MarshalByRefObject.)
Public methodGetSchema()Returns schema information for the data source of this SqlConnection. For more information about scheme, see SQL Server Schema Collections. (Overrides DbConnection.GetSchema().)
Public methodGetSchema(String)Returns schema information for the data source of this SqlConnection using the specified string for the schema name. (Overrides DbConnection.GetSchema(String).)
Public methodGetSchema(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[]).)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodInitializeLifetimeServiceObtains a lifetime service object to control the lifetime policy for this instance. (Inherited from MarshalByRefObject.)
Public methodOpenOpens a database connection with the property settings specified by the ConnectionString. (Overrides DbConnection.Open().)
Public methodOpenAsync()An asynchronous version of Open, which opens a database connection with the settings specified by the ConnectionString. This method invokes the virtual method OpenAsync with CancellationToken.None. (Inherited from DbConnection.)
Public methodOpenAsync(CancellationToken)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. (Overrides DbConnection.OpenAsync(CancellationToken).)
Public methodResetStatisticsIf statistics gathering is enabled, all values are reset to zero.
Public methodRetrieveStatisticsReturns a name value pair collection of statistics at the point in time the method is called.
Public methodToStringReturns a String containing the name of the Component, if any. This method should not be overridden. (Inherited from Component.)
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  NameDescription
Public eventDisposedOccurs when the component is disposed by a call to the Dispose method. (Inherited from Component.)
Public eventInfoMessageOccurs when SQL Server returns a warning or informational message.
Public eventStateChangeOccurs when the state of the event changes. (Inherited from DbConnection.)
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  NameDescription
Explicit interface implemetationPrivate methodICloneable.CloneCreates a new object that is a copy of the current instance.
Explicit interface implemetationPrivate methodIDbConnection.BeginTransaction()Begins a database transaction. (Inherited from DbConnection.)
Explicit interface implemetationPrivate methodIDbConnection.BeginTransaction(IsolationLevel)Begins a database transaction with the specified IsolationLevel value. (Inherited from DbConnection.)
Explicit interface implemetationPrivate methodIDbConnection.CreateCommandCreates and returns a DbCommand object that is associated with the current connection. (Inherited from DbConnection.)
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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.

NoteNote

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 (SqlConnection connection = new SqlConnection(connectionString))
    {
        connection.Open();
        // Do work here; connection closed on following line.
    }
NoteNote

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.

For more information about handling warning and informational messages from the server, see Connection Events. SQL Server engine errors and error messages are documented in SQL Server Books Online.

Caution noteCaution

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.

TopicLocation
How to: Create Connections to SQL Server DatabasesData Access in Visual Studio

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.

private static void CreateCommand(string queryString,
    string connectionString)
{
    using (SqlConnection connection = new SqlConnection(
               connectionString))
    {
        SqlCommand command = new SqlCommand(queryString, connection);
        command.Connection.Open();
        command.ExecuteNonQuery();
    }
}

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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