MSDN Documentation

Understanding ADO.NET Connection Strings

Connection strings are a fundamental part of using ADO.NET to connect to and interact with a data source. They provide the necessary information for the ADO.NET data provider to establish a connection.

What is a Connection String?

A connection string is a string that contains various parameters and their values, separated by semicolons, which are used to identify the data source and specify how to connect to it. These parameters can include information such as:

• The data source (e.g., server name, database file path).
• The name of the database.
• Authentication credentials (username, password, integrated security).
• Provider-specific settings.

Common Connection String Parameters

While specific parameters vary by data provider, here are some common ones:

SQL Server Connection Strings

For SQL Server, common parameters include:

• Server or Data Source: The name or IP address of the SQL Server instance.
• Database or Initial Catalog: The name of the database to connect to.
• User ID: The username for SQL Server authentication.
• Password: The password for SQL Server authentication.
• Integrated Security: Set to True or SSPI to use Windows authentication.

Example using SQL Server Authentication:

Server=myServerAddress;Database=myDataBase;User ID=myUsername;Password=myPassword;

Example using Windows Authentication:

Server=myServerAddress;Database=myDataBase;Integrated Security=True;

Example connecting to a SQL Server Express instance:

Server=.\SQLEXPRESS;Database=myDataBase;User ID=myUsername;Password=myPassword;

OleDb Connection Strings (for various OLE DB data sources like Access)

For OLE DB providers, you often need to specify the provider:

• Provider: The ProgID of the OLE DB provider (e.g., Microsoft.ACE.OLEDB.12.0 for newer Access databases, Microsoft.Jet.OLEDB.4.0 for older ones).
• Data Source: The path to the database file.

Example for Microsoft Access:

Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\mydatabases\myDatabase.accdb;Persist Security Info=False;User ID=admin;Password=;

ODBC Connection Strings

For ODBC data sources, you'll typically specify the driver:

• Driver: The name of the ODBC driver.
• Server, Database, Uid, Pwd: Similar to other providers.

Example using an ODBC Driver:

Driver={ODBC Driver 17 for SQL Server};Server=myServerName;Database=myDatabaseName;Uid=myUsername;Pwd=myPassword;

Key Considerations

• Security: Never hardcode sensitive credentials (like passwords) directly in your source code. Use configuration files, environment variables, or secure credential management systems.
• Provider Specificity: Always refer to the documentation for the specific ADO.NET data provider you are using for the correct syntax and available parameters.
• Data Source Names (DSNs): Some applications may use System DSNs or User DSNs configured on the operating system. Connection strings can reference these.
• Connection Pooling: ADO.NET automatically implements connection pooling for many providers, which can significantly improve performance by reusing established connections.

Building Connection Strings Programmatically

You can construct connection strings dynamically in your application code. For example, using C# with SqlConnectionStringBuilder:

// Using SqlConnectionStringBuilder in C#
            var builder = new SqlConnectionStringBuilder();
            builder.DataSource = "myServerAddress";
            builder.InitialCatalog = "myDataBase";
            builder.IntegratedSecurity = true;
            string connectionString = builder.ConnectionString;
            

This approach helps prevent syntax errors and makes your code more readable.

Note: The exact syntax and available parameters for connection strings can vary significantly between different data providers. Always consult the specific documentation for the provider you are using.