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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.

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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?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 285
def self.database_exists?(config)
  raise NotImplementedError
end

type_cast_config_to_boolean(config)

# 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

type_cast_config_to_integer(config)

# 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

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 502
def active?
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 280
def adapter_name
  self.class::ADAPTER_NAME
end

all_foreign_keys_valid?()

Override to check all foreign key constraints in a database.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 493
def all_foreign_keys_valid?
  true
end

clear_cache!()

Clear any caching the database adapter may be doing.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 553
def clear_cache!
  @lock.synchronize { @statements.clear } if @statements
end

close()

Check the connection back in to the connection pool

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 604
def close
  pool.checkin self
end

disable_extension(name)

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 450
def disable_extension(name)
end

disable_referential_integrity()

Override to turn off referential integrity while executing &block.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 488
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.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 526
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

disconnect!()

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 515
def disconnect!
  clear_cache!
  reset_transaction
end

enable_extension(name)

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 454
def enable_extension(name)
end

expire()

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 237
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.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 476
def extensions
  []
end

index_algorithms()

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 481
def index_algorithms
  {}
end

lease()

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 208
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

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.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 312
def prefetch_primary_key?(table_name = nil)
  false
end

prepared_statements()

prepared_statements?()

Also aliased as: prepared_statements
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 175
def prepared_statements?
  @prepared_statements && !prepared_statements_disabled_cache.include?(object_id)
end

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.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 141
def preventing_writes?
  return true if replica?
  return ActiveRecord::Base.connection_handler.prevent_writes if ActiveRecord.legacy_connection_handling
  return false if connection_klass.nil?

  connection_klass.current_preventing_writes
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.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 575
def raw_connection
  disable_lazy_transactions!
  @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.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 508
def reconnect!
  clear_cache!
  reset_transaction
end

replica?()

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 124
def replica?
  @config[:replica] || false
end

requires_reloading?()

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 558
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 542
def reset!
  # this should be overridden by concrete adapters
end

schema_cache()

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 227
def schema_cache
  @pool.get_schema_cache(self)
end

schema_cache=(cache)

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 231
def schema_cache=(cache)
  cache.connection = self
  @pool.set_schema_cache(cache)
end

supports_advisory_locks?()

Does this adapter support application-enforced advisory locking?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 305
def supports_advisory_locks?
  false
end

supports_bulk_alter?()

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 295
def supports_bulk_alter?
  false
end

supports_check_constraints?()

Does this adapter support creating check constraints?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 367
def supports_check_constraints?
  false
end

supports_comments?()

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 392
def supports_comments?
  false
end

supports_comments_in_create?()

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 397
def supports_comments_in_create?
  false
end

supports_common_table_expressions?()

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 416
def supports_common_table_expressions?
  false
end

supports_concurrent_connections?()

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 440
def supports_concurrent_connections?
  true
end

supports_datetime_with_precision?()

Does this adapter support datetime with precision?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 382
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?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 291
def supports_ddl_transactions?
  false
end

supports_explain?()

Does this adapter support explain?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 336
def supports_explain?
  false
end

supports_expression_index?()

Does this adapter support expression indices?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 331
def supports_expression_index?
  false
end

supports_extensions?()

Does this adapter support database extensions?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 346
def supports_extensions?
  false
end

supports_foreign_keys?()

Does this adapter support creating foreign key constraints?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 357
def supports_foreign_keys?
  false
end

supports_foreign_tables?()

Does this adapter support foreign/external tables?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 407
def supports_foreign_tables?
  false
end

supports_index_sort_order?()

Does this adapter support index sort order?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 321
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?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 352
def supports_indexes_in_create?
  false
end

supports_insert_conflict_target?()

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 436
def supports_insert_conflict_target?
  false
end

supports_insert_on_duplicate_skip?()

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 428
def supports_insert_on_duplicate_skip?
  false
end

supports_insert_on_duplicate_update?()

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 432
def supports_insert_on_duplicate_update?
  false
end

supports_insert_returning?()

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 424
def supports_insert_returning?
  false
end

supports_json?()

Does this adapter support json data type?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 387
def supports_json?
  false
end

supports_lazy_transactions?()

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 420
def supports_lazy_transactions?
  false
end

supports_materialized_views?()

Does this adapter support materialized views?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 377
def supports_materialized_views?
  false
end

supports_optimizer_hints?()

Does this adapter support optimizer hints?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 412
def supports_optimizer_hints?
  false
end

supports_partial_index?()

Does this adapter support partial indices?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 326
def supports_partial_index?
  false
end

supports_partitioned_indexes?()

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 316
def supports_partitioned_indexes?
  false
end

supports_savepoints?()

Does this adapter support savepoints?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 300
def supports_savepoints?
  false
end

supports_transaction_isolation?()

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 341
def supports_transaction_isolation?
  false
end

supports_validate_constraints?()

Does this adapter support creating invalid constraints?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 362
def supports_validate_constraints?
  false
end

supports_views?()

Does this adapter support views?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 372
def supports_views?
  false
end

supports_virtual_columns?()

Does this adapter support virtual columns?

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 402
def supports_virtual_columns?
  false
end

throw_away!()

Removes the connection from the pool and disconnect it.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 547
def throw_away!
  pool.remove self
  disconnect!
end

unprepared_statement()

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 271
def unprepared_statement
  cache = prepared_statements_disabled_cache.add?(object_id) if @prepared_statements
  yield
ensure
  cache&.delete(object_id)
end

use_metadata_table?()

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 128
def use_metadata_table?
  @config.fetch(:use_metadata_table, true)
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.

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 565
def verify!
  reconnect! unless active?
end

Instance Private methods

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

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 726
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