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 SchemaStatements are very useful.

Namespace
Methods
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Included Modules
Constants
ADAPTER_NAME = "Abstract".freeze
 
SIMPLE_INT = /\A\d+\z/
 
Attributes
[R] in_use?
[R] lock
[R] logger
[R] owner
[RW] pool
[R] prepared_statements
[R] schema_cache
[RW] visitor
Class Public methods
type_cast_config_to_boolean(config)

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 93
def self.type_cast_config_to_boolean(config)
  if config == "false"
    false
  else
    config
  end
end
type_cast_config_to_integer(config)

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 83
def self.type_cast_config_to_integer(config)
  if config.is_a?(Integer)
    config
  elsif config =~ SIMPLE_INT
    config.to_i
  else
    config
  end
end
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.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 380
def active?
end
adapter_name()

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

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 213
def adapter_name
  self.class::ADAPTER_NAME
end
clear_cache!()

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

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 424
def clear_cache!
  # this should be overridden by concrete adapters
end
close()

Check the connection back in to the connection pool

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 468
def close
  pool.checkin self
end
disable_extension(name)

This is meant to be implemented by the adapters that support extensions

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 337
def disable_extension(name)
end
disable_referential_integrity()

Override to turn off referential integrity while executing &block.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 371
def disable_referential_integrity
  yield
end
discard!()

Immediately forget this connection ever existed. Unlike disconnect!, this will not communicate with the server.

After calling this method, the behavior of all other methods becomes undefined. This is called internally just before a forked process gets rid of a connection that belonged to its parent.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 404
def discard!
  # This should be overridden by concrete adapters.
  #
  # Prevent @connection's finalizer from touching the socket, or
  # otherwise communicating with its server, when it is collected.
end
disconnect!()

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

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 393
def disconnect!
  clear_cache!
  reset_transaction
end
enable_extension(name)

This is meant to be implemented by the adapters that support extensions

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 341
def enable_extension(name)
end
expire()

this method must only be called while holding connection pool's mutex

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 170
def expire
  if in_use?
    if @owner != Thread.current
      raise ActiveRecordError, "Cannot expire connection, " \
        "it is owned by a different thread: #{@owner}. " \
        "Current thread: #{Thread.current}."
    end

    @idle_since = Concurrent.monotonic_time
    @owner = nil
  else
    raise ActiveRecordError, "Cannot expire connection, it is not currently leased."
  end
end
extensions()

A list of extensions, to be filled in by adapters that support them.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 359
def extensions
  []
end
index_algorithms()

A list of index algorithms, to be filled by adapters that support them.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 364
def index_algorithms
  {}
end
lease()

this method must only be called while holding connection pool's mutex

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 149
def lease
  if in_use?
    msg = "Cannot lease connection, ".dup
    if @owner == Thread.current
      msg << "it is already leased by the current thread."
    else
      msg << "it is already in use by a different thread: #{@owner}. " \
             "Current thread: #{Thread.current}."
    end
    raise ActiveRecordError, msg
  end

  @owner = Thread.current
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.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 240
def prefetch_primary_key?(table_name = nil)
  false
end
raw_connection()

Provides access to the underlying database driver for this adapter. For example, this method returns a Mysql2::Client object in case of Mysql2Adapter, and a PG::Connection object in case of PostgreSQLAdapter.

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

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 446
def raw_connection
  @connection
end
reconnect!()

Disconnects from the database if already connected, and establishes a new connection with the database. Implementors should call super if they override the default implementation.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 386
def reconnect!
  clear_cache!
  reset_transaction
end
requires_reloading?()

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

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 429
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.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 417
def reset!
  # this should be overridden by concrete adapters
end
schema_cache=(cache)

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 164
def schema_cache=(cache)
  cache.connection = self
  @schema_cache = cache
end
supports_advisory_locks?()

Does this adapter support application-enforced advisory locking?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 233
def supports_advisory_locks?
  false
end
supports_bulk_alter?()

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 223
def supports_bulk_alter?
  false
end
supports_comments?()

Does this adapter support metadata comments on database objects (tables, columns, indexes)?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 312
def supports_comments?
  false
end
supports_comments_in_create?()

Can comments for tables, columns, and indexes be specified in create/alter table statements?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 317
def supports_comments_in_create?
  false
end
supports_datetime_with_precision?()

Does this adapter support datetime with precision?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 302
def supports_datetime_with_precision?
  false
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?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 219
def supports_ddl_transactions?
  false
end
supports_explain?()

Does this adapter support explain?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 260
def supports_explain?
  false
end
supports_expression_index?()

Does this adapter support expression indices?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 255
def supports_expression_index?
  false
end
supports_extensions?()

Does this adapter support database extensions?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 270
def supports_extensions?
  false
end
supports_foreign_keys?()

Does this adapter support creating foreign key constraints?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 281
def supports_foreign_keys?
  false
end
supports_foreign_keys_in_create?()

Does this adapter support creating foreign key constraints in the same statement as creating the table?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 292
def supports_foreign_keys_in_create?
  supports_foreign_keys?
end
supports_foreign_tables?()

Does this adapter support foreign/external tables?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 332
def supports_foreign_tables?
  false
end
supports_index_sort_order?()

Does this adapter support index sort order?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 245
def supports_index_sort_order?
  false
end
supports_indexes_in_create?()

Does this adapter support creating indexes in the same statement as creating the table?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 276
def supports_indexes_in_create?
  false
end
supports_json?()

Does this adapter support json data type?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 307
def supports_json?
  false
end
supports_multi_insert?()

Does this adapter support multi-value insert?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 322
def supports_multi_insert?
  true
end
supports_partial_index?()

Does this adapter support partial indices?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 250
def supports_partial_index?
  false
end
supports_savepoints?()

Does this adapter support savepoints?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 228
def supports_savepoints?
  false
end
supports_transaction_isolation?()

Does this adapter support setting the isolation level for a transaction?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 265
def supports_transaction_isolation?
  false
end
supports_validate_constraints?()

Does this adapter support creating invalid constraints?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 286
def supports_validate_constraints?
  false
end
supports_views?()

Does this adapter support views?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 297
def supports_views?
  false
end
supports_virtual_columns?()

Does this adapter support virtual columns?

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 327
def supports_virtual_columns?
  false
end
unprepared_statement()

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 204
def unprepared_statement
  old_prepared_statements, @prepared_statements = @prepared_statements, false
  yield
ensure
  @prepared_statements = old_prepared_statements
end
verify!()

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.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 436
def verify!
  reconnect! unless active?
end
Instance Private methods
log(sql, name = "SQL", binds = [], type_casted_binds = [], statement_name = nil)

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 570
def log(sql, name = "SQL", binds = [], type_casted_binds = [], statement_name = nil) # :doc:
  @instrumenter.instrument(
    "sql.active_record",
    sql:               sql,
    name:              name,
    binds:             binds,
    type_casted_binds: type_casted_binds,
    statement_name:    statement_name,
    connection_id:     object_id) do
    begin
      @lock.synchronize do
        yield
      end
    rescue => e
      raise translate_exception_class(e, sql)
    end
  end
end