SqlConnection

SqlConnection is a data access class in the .NET data provider for SQL Server. It represents an open session to a SQL Server database and is used to establish a connection that can be used by commands to execute queries and other operations. In the .NET Framework and .NET Platform, it is provided by the System.Data.SqlClient namespace; in newer .NET projects the Microsoft.Data.SqlClient package is commonly used as a successor.

A SqlConnection exposes properties such as ConnectionString, Database, DataSource, ServerVersion, and State. Its primary operations are opening and closing the connection via Open and Close (or OpenAsync), changing the database with ChangeDatabase, and creating commands through CreateCommand. It participates in connection pooling by default, which reuses connections to improve performance.

Connection strings encode server address, database name, and authentication and security options. Typical parameters include Data Source (or Server), Initial Catalog, Integrated Security (for Windows authentication) or User ID and Password, as well as Encrypt and TrustServerCertificate. Pooling, Min/Max Pool Size, and other parameters can be specified as well.

Usage best practices emphasize acquiring the connection late, enclosing it in a using block (or ensuring disposal) to release resources promptly, and avoiding keeping connections open longer than necessary. Asynchronous methods such as OpenAsync support scalable I/O-bound operations. SqlConnection is designed to work with related classes such as SqlCommand, SqlDataReader, and SqlTransaction to perform queries, commands, and transactions.

Security considerations include using integrated security when possible, handling credentials securely, and enabling encryption if required by the server. See also: SqlCommand, SqlDataReader, SqlTransaction, SqlConnectionStringBuilder, Pooling.