Active Record 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
Attributes
[R] in_use
[R] in_use?
[R] last_use
[R] logger
[R] open_transactions
[RW] pool
[R] schema_cache
[RW] visitor
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 176
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 92
def adapter_name
  'Abstract'
end
case_insensitive_comparison(table, attribute, column, value)
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 259
def case_insensitive_comparison(table, attribute, column, value)
  table[attribute].lower.eq(table.lower(value))
end
case_sensitive_modifier(node)
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 255
def case_sensitive_modifier(node)
  node
end
clear_cache!()

Clear any caching the database adapter may be doing, for example clearing the prepared statement cache. This is database specific.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 205
def clear_cache!
  # this should be overridden by concrete adapters
end
close()

Check the connection back in to the connection pool

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 268
def close
  pool.checkin self
end
create_savepoint()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 246
def create_savepoint
end
current_savepoint_name()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 263
def current_savepoint_name
  "active_record_#{open_transactions}"
end
decrement_open_transactions()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 238
def decrement_open_transactions
  @open_transactions -= 1
end
disable_referential_integrity()

Override to turn off referential integrity while executing &block.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 167
def disable_referential_integrity
  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 188
def disconnect!
  @active = false
end
expire()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 86
def expire
  @in_use = false
end
increment_open_transactions()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 234
def increment_open_transactions
  @open_transactions += 1
end
lease()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 77
def lease
  synchronize do
    unless in_use
      @in_use   = true
      @last_use = Time.now
    end
  end
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 136
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 154
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 228
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 182
def reconnect!
  @active = true
end
release_savepoint()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 252
def release_savepoint
end
requires_reloading?()

Returns true if its required to reload the connection between requests for development mode. This is not the case for Ruby/MySQL and it's not necessary for any adapters except SQLite.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 211
def requires_reloading?
  false
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 198
def reset!
  # this should be overridden by concrete adapters
end
rollback_to_savepoint()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 249
def rollback_to_savepoint
end
substitute_at(column, index)

Returns a bind substitution value given a columnand list of current binds

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 160
def substitute_at(column, index)
  Arel::Nodes::BindParam.new '?'
end
supports_bulk_alter?()
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 122
def supports_bulk_alter?
  false
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 111
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 118
def supports_ddl_transactions?
  false
end
supports_explain?()

Does this adapter support explain? As of this writing sqlite3, mysql2, and postgresql are the only ones that do.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 147
def supports_explain?
  false
end
supports_index_sort_order?()

Does this adapter support index sort order?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 141
def supports_index_sort_order?
  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 98
def supports_migrations?
  false
end
supports_primary_key?()

Can this adapter determine the primary key for tables not attached to an Active Record 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 105
def supports_primary_key?
  false
end
supports_savepoints?()

Does this adapter support savepoints? PostgreSQL and MySQL do, SQLite < 3.6.8 does not.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 128
def supports_savepoints?
  false
end
transaction_joinable=(joinable)
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 242
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 218
def verify!(*ignored)
  reconnect! unless active?
end
Instance Protected methods
log(sql, name = "SQL", binds = [])
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 274
def log(sql, name = "SQL", binds = [])
  @instrumenter.instrument(
    "sql.active_record",
    :sql           => sql,
    :name          => name,
    :connection_id => object_id,
    :binds         => binds) { yield }
rescue Exception => e
  message = "#{e.class.name}: #{e.message}: #{sql}"
  @logger.debug message if @logger
  exception = translate_exception(e, message)
  exception.set_backtrace e.backtrace
  raise exception
end
translate_exception(e, message)
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 289
def translate_exception(e, message)
  # override in derived class
  ActiveRecord::StatementInvalid.new(message)
end