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
Constants
SIMPLE_INT = /\A\d+\z/
 
Attributes
[R] in_use
[R] in_use?
[R] last_use
[R] logger
[RW] pool
[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 85
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 77
def self.type_cast_config_to_integer(config)
  if 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 262
def active?
end
active_threadsafe?()

Adapter should redefine this if it needs a threadsafe way to approximate if the connection is active

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 267
def active_threadsafe?
  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 147
def adapter_name
  'Abstract'
end
case_insensitive_comparison(table, attribute, column, value)

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 343
def case_insensitive_comparison(table, attribute, column, value)
  table[attribute].lower.eq(table.lower(value))
end
case_sensitive_modifier(node)

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 339
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.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 299
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 352
def close
  pool.checkin self
end
create_savepoint(name = nil)

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 330
def create_savepoint(name = nil)
end
current_savepoint_name()

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 347
def current_savepoint_name
  "active_record_#{open_transactions}"
end
disable_extension(name)

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

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 223
def disable_extension(name)
end
disable_referential_integrity()

Override to turn off referential integrity while executing &block.

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 253
def disable_referential_integrity
  yield
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 281
def disconnect!
  clear_cache!
  reset_transaction
end
enable_extension(name)

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

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 227
def enable_extension(name)
end
expire()

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 129
def expire
  @in_use = false
end
extensions()

A list of extensions, to be filled in by adapters that support them. At the moment only postgresql does.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 232
def extensions
  []
end
index_algorithms()

A list of index algorithms, to be filled by adapters that support them. MySQL and PostgreSQL have support for them right now.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 238
def index_algorithms
  {}
end
lease()

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 115
def lease
  synchronize do
    unless in_use
      @in_use   = true
      @last_use = Time.now
    end
  end
end
open_transactions()

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 326
def open_transactions
  @transaction.number
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.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 191
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 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.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 322
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 274
def reconnect!
  clear_cache!
  reset_transaction
end
release_savepoint(name = nil)

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 336
def release_savepoint(name = nil)
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.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 305
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 292
def reset!
  # this should be overridden by concrete adapters
end
rollback_to_savepoint(name = nil)

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 333
def rollback_to_savepoint(name = nil)
end
schema_cache=(cache)

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 124
def schema_cache=(cache)
  cache.connection = self
  @schema_cache = cache
end
schema_creation()

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 111
def schema_creation
  SchemaCreation.new self
end
substitute_at(column, index)

Returns a bind substitution value given a bind index and column NOTE: The column param is currently being used by the sqlserver-adapter

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 246
def substitute_at(column, index)
  Arel::Nodes::BindParam.new '?'
end
supports_bulk_alter?()

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 177
def supports_bulk_alter?
  false
end
supports_count_distinct?()

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

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 166
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.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 173
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.

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 207
def supports_explain?
  false
end
supports_extensions?()

Does this adapter support database extensions? As of this writing only postgresql does.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 218
def supports_extensions?
  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 196
def supports_index_sort_order?
  false
end
supports_migrations?()

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

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 153
def supports_migrations?
  false
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 201
def supports_partial_index?
  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.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 160
def supports_primary_key?
  false
end
supports_savepoints?()

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

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 183
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 212
def supports_transaction_isolation?
  false
end
unprepared_statement()

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 137
def unprepared_statement
  old_prepared_statements, @prepared_statements = @prepared_statements, false
  old_visitor, @visitor = @visitor, unprepared_visitor
  yield
ensure
  @visitor, @prepared_statements = old_visitor, old_prepared_statements
end
unprepared_visitor()

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 133
def unprepared_visitor
  self.class::BindSubstitution.new self
end
valid_type?(type)

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 107
def valid_type?(type)
  true
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.

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 312
def verify!(*ignored)
  reconnect! unless active?
end
Instance Protected methods
log(sql, name = "SQL", binds = [], statement_name = nil)

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 366
def log(sql, name = "SQL", binds = [], statement_name = nil)
  @instrumenter.instrument(
    "sql.active_record",
    :sql            => sql,
    :name           => name,
    :connection_id  => object_id,
    :statement_name => statement_name,
    :binds          => binds) { yield }
rescue => e
  raise translate_exception_class(e, sql)
end
translate_exception(exception, message)

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 378
def translate_exception(exception, message)
  # override in derived class
  ActiveRecord::StatementInvalid.new(message, exception)
end
translate_exception_class(e, sql)

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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 358
def translate_exception_class(e, sql)
  message = "#{e.class.name}: #{e.message}: #{sql}"
  @logger.error message if @logger
  exception = translate_exception(e, message)
  exception.set_backtrace e.backtrace
  exception
end
without_prepared_statement?(binds)

Source: show | on GitHub 

# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 383
def without_prepared_statement?(binds)
  !@prepared_statements || binds.empty?
end