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.

Methods
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Included Modules
Instance Public methods
active?()

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.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 117
def active?
  @active != false
end
adapter_name()

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 49
def adapter_name
  'Abstract'
end
create_savepoint()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 182
def create_savepoint
end
current_savepoint_name()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 191
def current_savepoint_name
  "active_record_#{open_transactions}"
end
decrement_open_transactions()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 174
def decrement_open_transactions
  @open_transactions -= 1
end
disable_referential_integrity(&block)

Override to turn off referential integrity while executing &block.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 108
def disable_referential_integrity(&block)
  yield
end
disconnect!()

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 129
def disconnect!
  @active = false
end
increment_open_transactions()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 169
def increment_open_transactions
  @open_transactions ||= 0
  @open_transactions += 1
end
log_info(sql, name, ms)
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 195
def log_info(sql, name, ms)
  if @logger && @logger.debug?
    name = '%s (%.1fms)' % [name || 'SQL', ms]
    @logger.debug(format_log_entry(name, sql.squeeze(' ')))
  end
end
open_transactions()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 165
def open_transactions
  @open_transactions ||= 0
end
prefetch_primary_key?(table_name = nil)

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.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 89
def prefetch_primary_key?(table_name = nil)
  false
end
quote_table_name(name)

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 101
def quote_table_name(name)
  quote_column_name(name)
end
raw_connection()

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.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 161
def raw_connection
  @connection
end
reconnect!()

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 123
def reconnect!
  @active = true
end
release_savepoint()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 188
def release_savepoint
end
requires_reloading?()

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 144
def requires_reloading?
  true
end
reset!()

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.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 139
def reset!
  # this should be overridden by concrete adapters
end
rollback_to_savepoint()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 185
def rollback_to_savepoint
end
supports_count_distinct?()

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 68
def supports_count_distinct?
  true
end
supports_ddl_transactions?()

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.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 75
def supports_ddl_transactions?
  false
end
supports_migrations?()

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 55
def supports_migrations?
  false
end
supports_primary_key?()

Can this adapter determine the primary key for tables not attached to an ActiveRecord class, such as join tables? Backend specific, as the abstract adapter always returns false.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 62
def supports_primary_key?
  false
end
supports_savepoints?()

Does this adapter support savepoints? PostgreSQL and MySQL do, SQLite does not.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 81
def supports_savepoints?
  false
end
transaction_joinable=(joinable)
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 178
def transaction_joinable=(joinable)
  @transaction_joinable = joinable
end
verify!(*ignored)

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.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 151
def verify!(*ignored)
  reconnect! unless active?
end
Instance Protected methods
format_log_entry(message, dump = nil)
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 230
def format_log_entry(message, dump = nil)
  if ActiveRecord::Base.colorize_logging
    if @@row_even
      @@row_even = false
      message_color, dump_color = "4;36;1", "0;1"
    else
      @@row_even = true
      message_color, dump_color = "4;35;1", "0"
    end
    log_entry = "  \e[#{message_color}m#{message}\e[0m   "
    log_entry << "\e[#{dump_color}m%#{String === dump ? 's' : 'p'}\e[0m" % dump if dump
    log_entry
  else
    "%s  %s" % [message, dump]
  end
end
log(sql, name)
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 203
def log(sql, name)
  if block_given?
    result = nil
    ms = Benchmark.ms { result = yield }
    @runtime += ms
    log_info(sql, name, ms)
    result
  else
    log_info(sql, name, 0)
    nil
  end
rescue SystemExit, SignalException, NoMemoryError => e
  # Don't re-wrap these exceptions. They are probably not being caused by invalid
  # sql, but rather some external stimulus beyond the responsibilty of this code.
  # Additionaly, wrapping these exceptions with StatementInvalid would lead to
  #  meaningful loss of data, such as losing SystemExit#status.
  raise e
rescue Exception => e
  # Log message and raise exception.
  # Set last_verification to 0, so that connection gets verified
  # upon reentering the request loop
  @last_verification = 0
  message = "#{e.class.name}: #{e.message}: #{sql}"
  log_info(message, name, 0)
  raise ActiveRecord::StatementInvalid, message
end