ActiveRecord::ConnectionAdapters::AbstractAdapter

• activerecord/lib/active_record/connection_adapters/abstract_adapter.rb

ActiveRecord supports multiple database systems. AbstractAdapter and related classes form the abstraction layer which makes this possible. An AbstractAdapter represents a connection to a database, and provides an abstract interface for database-specific functionality such as establishing a connection, escaping values, building the right SQL fragments for ’:offset’ and ’:limit’ options, etc.

All the concrete database adapters follow the interface laid down in this class. ActiveRecord::Base.connection returns an AbstractAdapter object, which you can use.

Most of the methods in the adapter are useful during migrations. Most notably, the instance methods provided by SchemaStatement are very useful.

• active?
• adapter_name
• decrement_open_transactions
• disable_referential_integrity
• disconnect!
• format_log_entry
• increment_open_transactions
• log
• log_info
• open_transactions
• prefetch_primary_key?
• quote_table_name
• raw_connection
• reconnect!
• requires_reloading?
• reset!
• supports_count_distinct?
• supports_ddl_transactions?
• supports_migrations?
• verify!

• Quoting
• DatabaseStatements
• SchemaStatements
• QueryCache
• ActiveSupport::Callbacks

Checks whether the connection to the database is still active. This includes checking whether the database is actually capable of responding, i.e. whether the connection isn‘t stale.

Returns the human-readable name of the adapter. Use mixed case - one can always use downcase if needed.

Override to turn off referential integrity while executing &block.

Disconnects from the database if already connected. Otherwise, this method does nothing.

Should primary key values be selected from their corresponding sequence before the insert statement? If true, next_sequence_value is called before each insert to set the record‘s primary key. This is false for all adapters but Firebird.

Override to return the quoted table name. Defaults to column quoting.

Provides access to the underlying database driver for this adapter. For example, this method returns a Mysql object in case of MysqlAdapter, and a PGconn object in case of PostgreSQLAdapter.

This is useful for when you need to call a proprietary method such as PostgreSQL‘s lo_* methods.

Disconnects from the database if already connected, and establishes a new connection with the database.

Returns true if its safe to reload the connection between requests for development mode.

Reset the state of this connection, directing the DBMS to clear transactions and other connection-related server-side state. Usually a database-dependent operation.

The default implementation does nothing; the implementation should be overridden by concrete adapters.

Does this adapter support using DISTINCT within COUNT? This is true for all adapters except sqlite.

Does this adapter support DDL rollbacks in transactions? That is, would CREATE TABLE or ALTER TABLE get rolled back by a transaction? PostgreSQL, SQL Server, and others support this. MySQL and others do not.

Does this adapter support migrations? Backend specific, as the abstract adapter always returns false.

Checks whether the connection to the database is still active (i.e. not stale). This is done under the hood by calling active?. If the connection is no longer active, then this method will reconnect to the database.