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SqlConnection.ConnectionString Property

Gets or sets the string used to open a SQL Server database.

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

[SettingsBindableAttribute(true)]
public override string ConnectionString { get; set; }

Property Value

Type: System.String
The connection string that includes the source database name, and other parameters needed to establish the initial connection. The default value is an empty string.

Implements

IDbConnection.ConnectionString

ExceptionCondition
ArgumentException

An invalid connection string argument has been supplied, or a required connection string argument has not been supplied.

The ConnectionString is similar to an OLE DB connection string, but is not identical. Unlike OLE DB or ADO, the connection string that is returned is the same as the user-set ConnectionString, minus security information if the Persist Security Info value is set to false (default). The .NET Framework Data Provider for SQL Server does not persist or return the password in a connection string unless you set Persist Security Info to true.

You can use the ConnectionString property to connect to a database. The following example illustrates a typical connection string.

"Persist Security Info=False;Integrated Security=true;Initial Catalog=Northwind;server=(local)"

Use the new SqlConnectionStringBuilder to construct valid connection strings at run time. For more information, see Connection String Builders.

The ConnectionString property can be set only when the connection is closed. Many of the connection string values have corresponding read-only properties. When the connection string is set, these properties are updated, except when an error is detected. In this case, none of the properties are updated. SqlConnection properties return only those settings that are contained in the ConnectionString.

To connect to a local computer, specify "(local)" for the server. If a server name is not specified, a connection will be attempted to the default instance on the local computer.

Resetting the ConnectionString on a closed connection resets all connection string values (and related properties) including the password. For example, if you set a connection string that includes "Database= AdventureWorks", and then reset the connection string to "Data Source=myserver;Integrated Security=true", the Database property is no longer set to "AdventureWorks".

The connection string is parsed immediately after being set. If errors in syntax are found when parsing, a runtime exception, such as ArgumentException, is generated. Other errors can be found only when an attempt is made to open the connection.

The basic format of a connection string includes a series of keyword/value pairs separated by semicolons. The equal sign (=) connects each keyword and its value. To include values that contain a semicolon, single-quote character, or double-quote character, the value must be enclosed in double quotation marks. If the value contains both a semicolon and a double-quote character, the value can be enclosed in single quotation marks. The single quotation mark is also useful if the value starts with a double-quote character. Conversely, the double quotation mark can be used if the value starts with a single quotation mark. If the value contains both single-quote and double-quote characters, the quotation mark character used to enclose the value must be doubled every time it occurs within the value.

To include preceding or trailing spaces in the string value, the value must be enclosed in either single quotation marks or double quotation marks. Any leading or trailing spaces around integer, Boolean, or enumerated values are ignored, even if enclosed in quotation marks. However, spaces within a string literal keyword or value are preserved. Single or double quotation marks may be used within a connection string without using delimiters (for example, Data Source= my'Server or Data Source= my"Server), unless a quotation mark character is the first or last character in the value.

Keywords are not case sensitive.

The following table lists the valid names for keyword values within the ConnectionString.

Keyword

Default

Description

Addr

N/A

Synonym of Data Source.

Address

N/A

Synonym of Data Source.

App

N/A

Synonym of Application Name.

Application Name

N/A

The name of the application, or '.NET SQLClient Data Provider' if no application name is provided.

An application name can be 128 characters or less.

ApplicationIntent

ReadWrite

Declares the application workload type when connecting to a server. Possible values are ReadOnly and ReadWrite. For example:

ApplicationIntent=ReadOnly

For more information about SqlClient support for Always On Availability Groups, see SqlClient Support for High Availability, Disaster Recovery.

Asynchronous Processing

-or-

Async

'false'

When true, enables asynchronous operation support. Recognized values are true, false, yes, and no.

This property is ignored beginning in .NET Framework 4.5. For more information about SqlClient support for asynchronous programming, see Asynchronous Programming.

AttachDBFilename

-or-

Extended Properties

-or-

Initial File Name

N/A

The name of the primary database file, including the full path name of an attachable database. AttachDBFilename is only supported for primary data files with an .mdf extension.

If the value of the AttachDBFileName key is specified in the connection string, the database is attached and becomes the default database for the connection.

If this key is not specified and if the database was previously attached, the database will not be reattached. The previously attached database will be used as the default database for the connection.

If this key is specified together with the AttachDBFileName key, the value of this key will be used as the alias. However, if the name is already used in another attached database, the connection will fail.

The path may be absolute or relative by using the DataDirectory substitution string. If DataDirectory is used, the database file must exist within a subdirectory of the directory pointed to by the substitution string.

NoteNote

Remote server, HTTP, and UNC path names are not supported.

The database name must be specified with the keyword 'database' (or one of its aliases) as in the following:

"AttachDbFileName=|DataDirectory|\data\YourDB.mdf;integrated security=true;database=YourDatabase"

An error will be generated if a log file exists in the same directory as the data file and the 'database' keyword is used when attaching the primary data file. In this case, remove the log file. Once the database is attached, a new log file will be automatically generated based on the physical path.

Connect Timeout

-or-

Connection Timeout

-or-

Timeout

15

The length of time (in seconds) to wait for a connection to the server before terminating the attempt and generating an error.

Valid values are greater than or equal to 0 and less than or equal to 2147483647.

When opening a connection to a Azure SQL Database, set the connection timeout to 30 seconds.

Connection Lifetime

-or-

Load Balance Timeout

0

When a connection is returned to the pool, its creation time is compared with the current time, and the connection is destroyed if that time span (in seconds) exceeds the value specified by Connection Lifetime. This is useful in clustered configurations to force load balancing between a running server and a server just brought online.

A value of zero (0) causes pooled connections to have the maximum connection timeout.

ConnectRetryCount

1

Controls the number of reconnection attempts after the client identifies an idle connection failure. Valid values are 0 to 255. The default is 1. 0 means do not attempt to reconnect (disable connection resiliency).

For additional information about idle connection resiliency, see Technical Atricle – Idle Connection Resiliency.

ConnectRetryInterval

1

Specifies the time between each connection retry attempt (ConnectRetryCount). Valid values are 1 (default) to 60 seconds, applied after the first reconnection attempt. When a broken connection is detected, the client immediately attempts to reconnect; this is the first reconnection attempt and only occurs if ConnectRetryCount is greater than 0. If the first reconnection attempt fails and ConnectRetryCount is greater than 1, the client waits ConnectRetryInterval to try the second and subsequent reconnection attempts.

For additional information about idle connection resiliency, see Technical Atricle – Idle Connection Resiliency.

Context Connection

'false'

true if an in-process connection to SQL Server should be made.

Current Language

-or-

Language

N/A

Sets the language used for database server warning or error messages.

The language name can be 128 characters or less.

Data Source

-or-

Server

-or-

Address

-or-

Addr

-or-

Network Address

N/A

The name or network address of the instance of SQL Server to which to connect. The port number can be specified after the server name:

server=tcp:servername, portnumber

When specifying a local instance, always use (local). To force a protocol, add one of the following prefixes:

np:(local), tcp:(local), lpc:(local)

Beginning in .NET Framework 4.5, you can also connect to a LocalDB database as follows:

server=(localdb)\\myInstance

For more information about LocalDB, see SqlClient Support for LocalDB.

Data Source must use the TCP format or the Named Pipes format.

TCP format is as follows:

  • tcp:<host name>\<instance name>

  • tcp:<host name>,<TCP/IP port number>

The TCP format must start with the prefix "tcp:" and is followed by the database instance, as specified by a host name and an instance name.

The host name MUST be specified in one of the following ways:

  • NetBIOSName

  • IPv4Address

  • IPv6Address

The instance name is used to resolve to a particular TCP/IP port number on which a database instance is hosted. Alternatively, specifying a TCP/IP port number directly is also allowed. If both instance name and port number are not present, the default database instance is used.

The Named Pipes format is as follows:

  • np:\\<host name>\pipe\<pipe name>

The Named Pipes format MUST start with the prefix "np:" and is followed by a named pipe name.

The host name MUST be specified in one of the following ways:

  • NetBIOSName

  • IPv4Address

  • IPv6Address

The pipe name is used to identify the database instance to which the .NET Framework application will be connected.

If the value of the Network key is specified, the prefixes "tcp:" and "np:" should not be specified.

NoteNote

You can force the use of TCP instead of shared memory, either by prefixing tcp: to the server name in the connection string, or by using localhost.

Encrypt

'false'

When true, SQL Server uses SSL encryption for all data sent between the client and server if the server has a certificate installed. Recognized values are true, false, yes, and no. For more information, see Connection String Syntax.

Beginning in .NET Framework 4.5, when TrustServerCertificate is false and Encrypt is true, the server name (or IP address) in a SQL Server SSL certificate must exactly match the server name (or IP address) specified in the connection string. Otherwise, the connection attempt will fail. For information about support for certificates whose subject starts with a wildcard character (*), see Accepted wildcards used by server certificates for server authentication.

Enlist

'true'

true indicates that the SQL Server connection pooler automatically enlists the connection in the creation thread's current transaction context.

Failover Partner

N/A

The name of the failover partner server where database mirroring is configured.

If the value of this key is "", then Initial Catalog must be present, and its value must not be "".

The server name can be 128 characters or less.

If you specify a failover partner but the failover partner server is not configured for database mirroring and the primary server (specified with the Server keyword) is not available, then the connection will fail.

If you specify a failover partner and the primary server is not configured for database mirroring, the connection to the primary server (specified with the Server keyword) will succeed if the primary server is available.

Initial Catalog

-or-

Database

N/A

The name of the database.

The database name can be 128 characters or less.

Integrated Security

-or-

Trusted_Connection

'false'

When false, User ID and Password are specified in the connection. When true, the current Windows account credentials are used for authentication.

Recognized values are true, false, yes, no, and sspi (strongly recommended), which is equivalent to true.

If User ID and Password are specified and Integrated Security is set to true, the User ID and Password will be ignored and Integrated Security will be used.

SqlCredential is a more secure way to specify credentials for a connection that uses SQL Server Authentication (Integrated Security=false).

Max Pool Size

100

The maximum number of connections that are allowed in the pool.

Valid values are greater than or equal to 1. Values that are less than Min Pool Size generate an error.

Min Pool Size

0

The minimum number of connections that are allowed in the pool.

Valid values are greater than or equal to 0. Zero (0) in this field means no minimum connections are initially opened.

Values that are greater than Max Pool Size generate an error.

MultipleActiveResultSets

'false'

When true, an application can maintain multiple active result sets (MARS). When false, an application must process or cancel all result sets from one batch before it can execute any other batch on that connection.

Recognized values are true and false.

For more information, see Multiple Active Result Sets (MARS).

MultiSubnetFailover

FALSE

Always specify multiSubnetFailover=True when connecting to the availability group listener of a SQL Server 2012 (or later) availability group or a SQL Server 2012 (or later) Failover Cluster Instance. multiSubnetFailover=True configures SqlClient to provide faster detection of and connection to the (currently) active server. Possible values are Yes and No, True and False or 1 and 0. For example:

MultiSubnetFailover=True

The default is False. For more information about SqlClient's support for Always On AGs, see SqlClient Support for High Availability, Disaster Recovery.

Network Library

-or-

Network

-or-

Net

N/A

The network library used to establish a connection to an instance of SQL Server. Supported values include:

dbnmpntw (Named Pipes)

dbmsrpcn (Multiprotocol, Windows RPC)

dbmsadsn (Apple Talk)

dbmsgnet (VIA)

dbmslpcn (Shared Memory)

dbmsspxn (IPX/SPX)

dbmssocn (TCP/IP)

Dbmsvinn (Banyan Vines)

The corresponding network DLL must be installed on the system to which you connect. If you do not specify a network and you use a local server (for example, "." or "(local)"), shared memory is used. In this example, the network library is Win32 Winsock TCP/IP (dbmssocn), and 1433 is the port being used.

Network Library=dbmssocn;Data Source=000.000.000.000,1433;

Packet Size

8000

Size in bytes of the network packets used to communicate with an instance of SQL Server.

The packet size can be greater than or equal to 512 and less than or equal to 32768.

Password

-or-

PWD

N/A

The password for the SQL Server account logging on. Not recommended. To maintain a high level of security, we strongly recommend that you use the Integrated Security or Trusted_Connection keyword instead. SqlCredential is a more secure way to specify credentials for a connection that uses SQL Server Authentication.

The password must be 128 characters or less.

Persist Security Info

-or-

PersistSecurityInfo

'false'

When set to false or no (strongly recommended), security-sensitive information, such as the password, is not returned as part of the connection if the connection is open or has ever been in an open state. Resetting the connection string resets all connection string values including the password. Recognized values are true, false, yes, and no.

Pooling

'true'

When the value of this key is set to true, any newly created connection will be added to the pool when closed by the application. In a next attempt to open the same connection, that connection will be drawn from the pool.

Connections are considered the same if they have the same connection string. Different connections have different connection strings.

The value of this key can be "true", "false", "yes", or "no".

Replication

'false'

true if replication is supported using the connection.

Transaction Binding

Implicit Unbind

Controls connection association with an enlisted System.Transactions transaction.

Possible values are:

Transaction Binding=Implicit Unbind;

Transaction Binding=Explicit Unbind;

Implicit Unbind causes the connection to detach from the transaction when it ends. After detaching, additional requests on the connection are performed in autocommit mode. The System.Transactions.Transaction.Current property is not checked when executing requests while the transaction is active. After the transaction has ended, additional requests are performed in autocommit mode.

If the system ends the transaction (in the scope of a using block) before the last command completes, it will throw InvalidOperationException.

Explicit Unbind causes the connection to remain attached to the transaction until the connection is closed or an explicit SqlConnection.TransactionEnlist(null) is called. Beginning in .NET Framework 4, changes to Implicit Unbind make Explicit Unbind obsolete. An InvalidOperationException is thrown if Transaction.Current is not the enlisted transaction or if the enlisted transaction is not active.

TrustServerCertificate

'false'

When set to true, SSL is used to encrypt the channel when bypassing walking the certificate chain to validate trust. If TrustServerCertificate is set to true and Encrypt is set to false, the channel is not encrypted. Recognized values are true, false, yes, and no. For more information, see Connection String Syntax.

Type System Version

N/A

A string value that indicates the type system the application expects. The functionality available to a client application is dependent on the version of SQL Server and the compatibility level of the database. Explicitly setting the type system version that the client application was written for avoids potential problems that could cause an application to break if a different version of SQL Server is used.

NoteNote

The type system version cannot be set for common language runtime (CLR) code executing in-process in SQL Server. For more information, see SQL Server Common Language Runtime Integration.

Possible values are:

Type System Version=SQL Server 2012;

Type System Version=SQL Server 2008;

Type System Version=SQL Server 2005;

Type System Version=Latest;

Type System Version=SQL Server 2012; specifies that the application will require version 11.0.0.0 of Microsoft.SqlServer.Types.dll. The other Type System Version settings will require version 10.0.0.0 of Microsoft.SqlServer.Types.dll.

Latest is obsolete and should not be used. Latest is equivalent to Type System Version=SQL Server 2008;.

User ID

-or-

UID

-or-

N/A

The SQL Server login account. Not recommended. To maintain a high level of security, we strongly recommend that you use the Integrated Security or Trusted_Connection keywords instead. SqlCredential is a more secure way to specify credentials for a connection that uses SQL Server Authentication.

The user ID must be 128 characters or less.

User Instance

'false'

A value that indicates whether to redirect the connection from the default SQL Server Express instance to a runtime-initiated instance running under the account of the caller.

Workstation ID

-or-

WSID

The local computer name

The name of the workstation connecting to SQL Server.

The ID must be 128 characters or less.

The following list contains the valid names for connection pooling values within the ConnectionString. For more information, see SQL Server Connection Pooling (ADO.NET).

  • Connection Lifetime (or Load Balance Timeout)

  • Enlist

  • Max Pool Size

  • Min Pool Size

  • Pooling

When you are setting keyword or connection pooling values that require a Boolean value, you can use 'yes' instead of 'true', and 'no' instead of 'false'. Integer values are represented as strings.

NoteNote

The .NET Framework Data Provider for SQL Server uses its own protocol to communicate with SQL Server. Therefore, it does not support the use of an ODBC data source name (DSN) when connecting to SQL Server because it does not add an ODBC layer.

NoteNote

Universal data link (UDL) files are not supported for the .NET Framework Data Provider for SQL Server.

Caution noteCaution

In this release, the application should use caution when constructing a connection string based on user input (for example when retrieving user ID and password information from a dialog box, and appending it to the connection string). The application should make sure that a user cannot embed additional connection string parameters in these values (for example, entering a password as "validpassword;database=somedb" in an attempt to attach to a different database). If you need to construct connection strings based on user input, use the new SqlConnectionStringBuilder, which validates the connection string and helps to eliminate this problem. See Connection String Builders for more information.

The following example creates a SqlConnection and sets the ConnectionString property before opening the connection.

private static void OpenSqlConnection()
{
    string connectionString = GetConnectionString();

    using (SqlConnection connection = new SqlConnection())
    {
        connection.ConnectionString = connectionString;

        connection.Open();

        Console.WriteLine("State: {0}", connection.State);
        Console.WriteLine("ConnectionString: {0}",
            connection.ConnectionString);
    }
}

static private string GetConnectionString()
{
    // To avoid storing the connection string in your code,  
    // you can retrieve it from a configuration file. 
    return "Data Source=MSSQL1;Initial Catalog=AdventureWorks;"
        + "Integrated Security=true;";
}

.NET Framework

Supported in: 4.6, 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.

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