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

Class

Methods

Included Modules

Constants

ADAPTER_NAME = "Abstract"
COMMENT_REGEX = %r{(?:--.*\n)|/\*(?:[^*]|\*[^/])*\*/}m
SIMPLE_INT = /\A\d+\z/
TYPE_MAP = Type::TypeMap.new.tap { |m| initialize_type_map(m) }

Attributes

[R] in_use?
[R] lock
[R] logger
[R] owner
[RW] pool
[R] visitor

Class Public methods

database_exists?(config)

Does the database for this adapter exist?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 289
      def self.database_exists?(config)
        raise NotImplementedError
      end
🔎 See on GitHub

type_cast_config_to_boolean(config)

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 57
      def self.type_cast_config_to_boolean(config)
        if config == "false"
          false
        else
          config
        end
      end
🔎 See on GitHub

type_cast_config_to_integer(config)

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 47
      def self.type_cast_config_to_integer(config)
        if config.is_a?(Integer)
          config
        elsif SIMPLE_INT.match?(config)
          config.to_i
        else
          config
        end
      end
🔎 See on GitHub

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 code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 515
      def active?
      end
🔎 See on GitHub

adapter_name()

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

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 284
      def adapter_name
        self.class::ADAPTER_NAME
      end
🔎 See on GitHub

all_foreign_keys_valid?()

Override to check all foreign key constraints in a database.

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 506
      def all_foreign_keys_valid?
        true
      end
🔎 See on GitHub

clear_cache!()

Clear any caching the database adapter may be doing.

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 566
      def clear_cache!
        @lock.synchronize { @statements.clear } if @statements
      end
🔎 See on GitHub

close()

Check the connection back in to the connection pool

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 621
      def close
        pool.checkin self
      end
🔎 See on GitHub

disable_extension(name)

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

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 459
      def disable_extension(name)
      end
🔎 See on GitHub

disable_referential_integrity()

Override to turn off referential integrity while executing &block.

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 501
      def disable_referential_integrity
        yield
      end
🔎 See on GitHub

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 code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 539
      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.
        if schema_cache.connection == self
          schema_cache.connection = nil
        end
      end
🔎 See on GitHub

disconnect!()

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

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 528
      def disconnect!
        clear_cache!
        reset_transaction
      end
🔎 See on GitHub

enable_extension(name)

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

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 463
      def enable_extension(name)
      end
🔎 See on GitHub

expire()

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

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 241
      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 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
          @owner = nil
        else
          raise ActiveRecordError, "Cannot expire connection, it is not currently leased."
        end
      end
🔎 See on GitHub

extensions()

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

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 489
      def extensions
        []
      end
🔎 See on GitHub

index_algorithms()

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

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 494
      def index_algorithms
        {}
      end
🔎 See on GitHub

lease()

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

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 200
      def lease
        if in_use?
          msg = +"Cannot lease connection, "
          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
🔎 See on GitHub

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 code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 316
      def prefetch_primary_key?(table_name = nil)
        false
      end
🔎 See on GitHub

prepared_statements()

Alias for: prepared_statements?

prepared_statements?()

Also aliased as: prepared_statements
📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 167
      def prepared_statements?
        @prepared_statements && !prepared_statements_disabled_cache.include?(object_id)
      end
🔎 See on GitHub

preventing_writes?()

Determines whether writes are currently being prevented.

Returns true if the connection is a replica.

If the application is using legacy handling, returns true if connection_handler.prevent_writes is set.

If the application is using the new connection handling will return true based on current_preventing_writes.

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 133
      def preventing_writes?
        return true if replica?
        return ActiveRecord::Base.connection_handler.prevent_writes if ActiveRecord.legacy_connection_handling
        return false if connection_class.nil?

        connection_class.current_preventing_writes
      end
🔎 See on GitHub

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.

Active Record cannot track if the database is getting modified using this client. If that is the case, generally you’ll want to invalidate the query cache using ActiveRecord::Base.clear_query_cache.

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 592
      def raw_connection
        disable_lazy_transactions!
        @connection
      end
🔎 See on GitHub

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 code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 521
      def reconnect!
        clear_cache!
        reset_transaction
      end
🔎 See on GitHub

replica?()

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 116
      def replica?
        @config[:replica] || false
      end
🔎 See on GitHub

requires_reloading?()

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

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 571
      def requires_reloading?
        false
      end
🔎 See on GitHub

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 code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 555
      def reset!
        # this should be overridden by concrete adapters
      end
🔎 See on GitHub

role()

The role (e.g. :writing) for the current connection. In a non-multi role application, :writing is returned.

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 221
      def role
        @pool.role
      end
🔎 See on GitHub

schema_cache()

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 231
      def schema_cache
        @pool.get_schema_cache(self)
      end
🔎 See on GitHub

schema_cache=(cache)

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 235
      def schema_cache=(cache)
        cache.connection = self
        @pool.set_schema_cache(cache)
      end
🔎 See on GitHub

schema_version()

Returns the version identifier of the schema currently available in the database. This is generally equal to the number of the highest- numbered migration that has been executed, or 0 if no schema information is present / the database is empty.

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 656
      def schema_version
        migration_context.current_version
      end
🔎 See on GitHub

shard()

The shard (e.g. :default) for the current connection. In a non-sharded application, :default is returned.

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 227
      def shard
        @pool.shard
      end
🔎 See on GitHub

supports_advisory_locks?()

Does this adapter support application-enforced advisory locking?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 309
      def supports_advisory_locks?
        false
      end
🔎 See on GitHub

supports_bulk_alter?()

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 299
      def supports_bulk_alter?
        false
      end
🔎 See on GitHub

supports_check_constraints?()

Does this adapter support creating check constraints?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 376
      def supports_check_constraints?
        false
      end
🔎 See on GitHub

supports_comments?()

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

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 401
      def supports_comments?
        false
      end
🔎 See on GitHub

supports_comments_in_create?()

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

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 406
      def supports_comments_in_create?
        false
      end
🔎 See on GitHub

supports_common_table_expressions?()

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 425
      def supports_common_table_expressions?
        false
      end
🔎 See on GitHub

supports_concurrent_connections?()

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 449
      def supports_concurrent_connections?
        true
      end
🔎 See on GitHub

supports_datetime_with_precision?()

Does this adapter support datetime with precision?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 391
      def supports_datetime_with_precision?
        false
      end
🔎 See on GitHub

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 code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 295
      def supports_ddl_transactions?
        false
      end
🔎 See on GitHub

supports_deferrable_constraints?()

Does this adapter support creating deferrable constraints?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 371
      def supports_deferrable_constraints?
        false
      end
🔎 See on GitHub

supports_explain?()

Does this adapter support explain?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 340
      def supports_explain?
        false
      end
🔎 See on GitHub

supports_expression_index?()

Does this adapter support expression indices?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 335
      def supports_expression_index?
        false
      end
🔎 See on GitHub

supports_extensions?()

Does this adapter support database extensions?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 350
      def supports_extensions?
        false
      end
🔎 See on GitHub

supports_foreign_keys?()

Does this adapter support creating foreign key constraints?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 361
      def supports_foreign_keys?
        false
      end
🔎 See on GitHub

supports_foreign_tables?()

Does this adapter support foreign/external tables?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 416
      def supports_foreign_tables?
        false
      end
🔎 See on GitHub

supports_index_sort_order?()

Does this adapter support index sort order?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 325
      def supports_index_sort_order?
        false
      end
🔎 See on GitHub

supports_indexes_in_create?()

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

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 356
      def supports_indexes_in_create?
        false
      end
🔎 See on GitHub

supports_insert_conflict_target?()

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 445
      def supports_insert_conflict_target?
        false
      end
🔎 See on GitHub

supports_insert_on_duplicate_skip?()

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 437
      def supports_insert_on_duplicate_skip?
        false
      end
🔎 See on GitHub

supports_insert_on_duplicate_update?()

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 441
      def supports_insert_on_duplicate_update?
        false
      end
🔎 See on GitHub

supports_insert_returning?()

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 433
      def supports_insert_returning?
        false
      end
🔎 See on GitHub

supports_json?()

Does this adapter support json data type?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 396
      def supports_json?
        false
      end
🔎 See on GitHub

supports_lazy_transactions?()

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 429
      def supports_lazy_transactions?
        false
      end
🔎 See on GitHub

supports_materialized_views?()

Does this adapter support materialized views?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 386
      def supports_materialized_views?
        false
      end
🔎 See on GitHub

supports_optimizer_hints?()

Does this adapter support optimizer hints?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 421
      def supports_optimizer_hints?
        false
      end
🔎 See on GitHub

supports_partial_index?()

Does this adapter support partial indices?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 330
      def supports_partial_index?
        false
      end
🔎 See on GitHub

supports_partitioned_indexes?()

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 320
      def supports_partitioned_indexes?
        false
      end
🔎 See on GitHub

supports_savepoints?()

Does this adapter support savepoints?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 304
      def supports_savepoints?
        false
      end
🔎 See on GitHub

supports_transaction_isolation?()

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

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 345
      def supports_transaction_isolation?
        false
      end
🔎 See on GitHub

supports_validate_constraints?()

Does this adapter support creating invalid constraints?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 366
      def supports_validate_constraints?
        false
      end
🔎 See on GitHub

supports_views?()

Does this adapter support views?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 381
      def supports_views?
        false
      end
🔎 See on GitHub

supports_virtual_columns?()

Does this adapter support virtual columns?

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 411
      def supports_virtual_columns?
        false
      end
🔎 See on GitHub

throw_away!()

Removes the connection from the pool and disconnect it.

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 560
      def throw_away!
        pool.remove self
        disconnect!
      end
🔎 See on GitHub

unprepared_statement()

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 275
      def unprepared_statement
        cache = prepared_statements_disabled_cache.add?(object_id) if @prepared_statements
        yield
      ensure
        cache&.delete(object_id)
      end
🔎 See on GitHub

use_metadata_table?()

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 120
      def use_metadata_table?
        @config.fetch(:use_metadata_table, true)
      end
🔎 See on GitHub

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 code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 578
      def verify!
        reconnect! unless active?
      end
🔎 See on GitHub

Instance Private methods

log(sql, name = "SQL", binds = [], type_casted_binds = [], statement_name = nil, async: false, &block)

📝 Source code 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 742
        def log(sql, name = "SQL", binds = [], type_casted_binds = [], statement_name = nil, async: false, &block) # :doc:
          @instrumenter.instrument(
            "sql.active_record",
            sql:               sql,
            name:              name,
            binds:             binds,
            type_casted_binds: type_casted_binds,
            statement_name:    statement_name,
            async:             async,
            connection:        self) do
            @lock.synchronize(&block)
          rescue => e
            raise translate_exception_class(e, sql, binds)
          end
        end
🔎 See on GitHub