Docs4dev
Docs
rails / 5.1 / activerecord / connectionadapters / abstractadapter.html

class ActiveRecord::ConnectionAdapters::AbstractAdapter

Parent:
Object
Included modules:
ActiveSupport::Callbacks, ActiveRecord::ConnectionAdapters::Quoting, ActiveRecord::ConnectionAdapters::DatabaseStatements, ActiveRecord::ConnectionAdapters::SchemaStatements, ActiveRecord::ConnectionAdapters::DatabaseLimits, ActiveRecord::ConnectionAdapters::QueryCache, ActiveRecord::ConnectionAdapters::ColumnDumper, ActiveRecord::ConnectionAdapters::Savepoints

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.

Constants

ADAPTER_NAME
SIMPLE_INT

Attributes

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

Public Class Methods

type_cast_config_to_boolean(config) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 89
def self.type_cast_config_to_boolean(config)
  if config == "false"
    false
  else
    config
  end
end
type_cast_config_to_integer(config) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 81
def self.type_cast_config_to_integer(config)
  if config =~ SIMPLE_INT
    config.to_i
  else
    config
  end
end

Public Instance Methods

active?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 397
def active?
end

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.

adapter_name() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 230
def adapter_name
  self.class::ADAPTER_NAME
end

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

clear_cache!() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 428
def clear_cache!
  # this should be overridden by concrete adapters
end

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

close() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 475
def close
  pool.checkin self
end

Check the connection back in to the connection pool

collector() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 144
def collector
  if prepared_statements
    SQLString.new
  else
    BindCollector.new
  end
end
disable_extension(name) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 354
def disable_extension(name)
end

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

disable_referential_integrity() { || ... } Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 388
def disable_referential_integrity
  yield
end

Override to turn off referential integrity while executing &block.

disconnect!() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 410
def disconnect!
  clear_cache!
  reset_transaction
end

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

enable_extension(name) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 358
def enable_extension(name)
end

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

expire() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 194
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

    @owner = nil
  else
    raise ActiveRecordError, "Cannot expire connection, it is not currently leased."
  end
end

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

extensions() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 376
def extensions
  []
end

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

index_algorithms() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 381
def index_algorithms
  {}
end

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

lease() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 173
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

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

prefetch_primary_key?(table_name = nil) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 267
def prefetch_primary_key?(table_name = nil)
  false
end

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.

raw_connection() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 453
def raw_connection
  @connection
end

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.

reconnect!() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 403
def reconnect!
  clear_cache!
  reset_transaction
end

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.

requires_reloading?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 433
def requires_reloading?
  false
end

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

reset!() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 421
def reset!
  # this should be overridden by concrete adapters
end

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.

schema_cache=(cache) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 188
def schema_cache=(cache)
  cache.connection = self
  @schema_cache = cache
end
schema_creation() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 160
def schema_creation
  SchemaCreation.new self
end
supports_advisory_locks?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 260
def supports_advisory_locks?
  false
end

Does this adapter support application-enforced advisory locking?

supports_bulk_alter?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 250
def supports_bulk_alter?
  false
end
supports_comments?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 334
def supports_comments?
  false
end

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

supports_comments_in_create?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 339
def supports_comments_in_create?
  false
end

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

supports_datetime_with_precision?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 324
def supports_datetime_with_precision?
  false
end

Does this adapter support datetime with precision?

supports_ddl_transactions?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 246
def supports_ddl_transactions?
  false
end

Does this adapter support DDL rollbacks in transactions? That is, would CREATE TABLE or ALTER TABLE get rolled back by a transaction?

supports_explain?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 287
def supports_explain?
  false
end

Does this adapter support explain?

supports_expression_index?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 282
def supports_expression_index?
  false
end

Does this adapter support expression indices?

supports_extensions?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 297
def supports_extensions?
  false
end

Does this adapter support database extensions?

supports_foreign_keys?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 308
def supports_foreign_keys?
  false
end

Does this adapter support creating foreign key constraints?

supports_foreign_keys_in_create?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 314
def supports_foreign_keys_in_create?
  supports_foreign_keys?
end

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

supports_index_sort_order?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 272
def supports_index_sort_order?
  false
end

Does this adapter support index sort order?

supports_indexes_in_create?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 303
def supports_indexes_in_create?
  false
end

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

supports_json?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 329
def supports_json?
  false
end

Does this adapter support json data type?

supports_multi_insert?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 344
def supports_multi_insert?
  true
end

Does this adapter support multi-value insert?

supports_partial_index?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 277
def supports_partial_index?
  false
end

Does this adapter support partial indices?

supports_savepoints?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 255
def supports_savepoints?
  false
end

Does this adapter support savepoints?

supports_transaction_isolation?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 292
def supports_transaction_isolation?
  false
end

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

supports_views?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 319
def supports_views?
  false
end

Does this adapter support views?

supports_virtual_columns?() Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 349
def supports_virtual_columns?
  false
end

Does this adapter support virtual columns?

unprepared_statement() { || ... } Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 221
def unprepared_statement
  old_prepared_statements, @prepared_statements = @prepared_statements, false
  yield
ensure
  @prepared_statements = old_prepared_statements
end
verify!(*ignored) Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 440
def verify!(*ignored)
  if ignored.size > 0
    ActiveSupport::Deprecation.warn("Passing arguments to #verify method of the connection has no effect and has been deprecated. Please remove all arguments from the #verify method call.")
  end
  reconnect! unless active?
end

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.

Private Instance Methods

log(sql, name = "SQL", binds = [], type_casted_binds = [], statement_name = nil) { || ... } Show source 
# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 603
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
      @lock.synchronize do
        yield
      end
    end
rescue => e
  raise translate_exception_class(e, sql)
end

© 2004–2018 David Heinemeier Hansson
Licensed under the MIT License.