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::Core#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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 81 def self.type_cast_config_to_boolean(config) if config == "false" false else config end end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 73 def self.type_cast_config_to_integer(config) if config =~ SIMPLE_INT config.to_i else config end 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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 315 def active? end
Returns the human-readable name of the adapter. Use mixed case - one can always use downcase if needed.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 208 def adapter_name 'Abstract' end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 404 def case_insensitive_comparison(table, attribute, column, value) table[attribute].lower.eq(table.lower(value)) end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 400 def case_sensitive_modifier(node) node end
Clear any caching the database adapter may be doing, for example clearing the prepared statement cache. This is database specific.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 346 def clear_cache! # this should be overridden by concrete adapters end
Check the connection back in to the connection pool
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 413 def close pool.checkin self end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 391 def create_savepoint end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 408 def current_savepoint_name "active_record_#{open_transactions}" end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 381 def decrement_open_transactions ActiveSupport::Deprecation.warn "#decrement_open_transactions is deprecated and has no effect" end
Override to turn off referential integrity while executing
&block
.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 306 def disable_referential_integrity yield end
Disconnects from the database if already connected. Otherwise, this method does nothing.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 328 def disconnect! clear_cache! reset_transaction end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 191 def expire @in_use = false end
A list of extensions, to be filled in by adapters that support them. At the moment only postgresql does.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 285 def extensions [] end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 377 def increment_open_transactions ActiveSupport::Deprecation.warn "#increment_open_transactions is deprecated and has no effect" end
A list of index algorithms, to be filled by adapters that support them. MySQL and PostgreSQL have support for them right now.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 291 def index_algorithms {} end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 177 def lease synchronize do unless in_use @in_use = true @last_use = Time.now end end end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 373 def open_transactions @transaction.number 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. This is false for all adapters but Firebird.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 252 def prefetch_primary_key?(table_name = nil) false end
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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 369 def raw_connection @connection 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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 321 def reconnect! clear_cache! reset_transaction end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 397 def release_savepoint end
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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 352 def requires_reloading? false 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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 339 def reset! # this should be overridden by concrete adapters end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 394 def rollback_to_savepoint end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 186 def schema_cache=(cache) cache.connection = self @schema_cache = cache end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 173 def schema_creation SchemaCreation.new self end
Returns a bind substitution value given a column
and list of
current binds
.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 299 def substitute_at(column, index) Arel::Nodes::BindParam.new '?' end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 238 def supports_bulk_alter? false end
Does this adapter support using DISTINCT within COUNT? This is
true
for all adapters except sqlite.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 227 def supports_count_distinct? true end
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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 234 def supports_ddl_transactions? false end
Does this adapter support explain? As of this writing sqlite3, mysql2, and postgresql are the only ones that do.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 268 def supports_explain? false end
Does this adapter support database extensions? As of this writing only postgresql does.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 279 def supports_extensions? false end
Does this adapter support index sort order?
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 257 def supports_index_sort_order? false end
Does this adapter support migrations? Backend specific, as the abstract
adapter always returns false
.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 214 def supports_migrations? false end
Does this adapter support partial indices?
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 262 def supports_partial_index? false end
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
.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 221 def supports_primary_key? false end
Does this adapter support savepoints? PostgreSQL and MySQL do, SQLite < 3.6.8 does not.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 244 def supports_savepoints? false end
Does this adapter support setting the isolation level for a transaction?
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 273 def supports_transaction_isolation? false end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 385 def transaction_joinable=(joinable) message = "#transaction_joinable= is deprecated. Please pass the :joinable option to #begin_transaction instead." ActiveSupport::Deprecation.warn message @transaction.joinable = joinable end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 199 def unprepared_statement old, @visitor = @visitor, unprepared_visitor yield ensure @visitor = old end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 195 def unprepared_visitor self.class::BindSubstitution.new self end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 104 def valid_type?(type) true 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.
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 359 def verify!(*ignored) reconnect! unless active? end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 419 def log(sql, name = "SQL", binds = []) @instrumenter.instrument( "sql.active_record", :sql => sql, :name => name, :connection_id => object_id, :binds => binds) { yield } rescue => e message = "#{e.class.name}: #{e.message}: #{sql}" @logger.error message if @logger exception = translate_exception(e, message) exception.set_backtrace e.backtrace raise exception end
# File lib/active_record/connection_adapters/abstract_adapter.rb, line 434 def translate_exception(exception, message) # override in derived class ActiveRecord::StatementInvalid.new(message, exception) end