ActiveRecord 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.
- active?
- adapter_name
- create_savepoint
- current_savepoint_name
- decrement_open_transactions
- disable_referential_integrity
- disconnect!
- format_log_entry
- increment_open_transactions
- log
- log_info
- open_transactions
- prefetch_primary_key?
- quote_table_name
- raw_connection
- reconnect!
- release_savepoint
- requires_reloading?
- reset!
- rollback_to_savepoint
- supports_count_distinct?
- supports_ddl_transactions?
- supports_migrations?
- supports_primary_key?
- supports_savepoints?
- transaction_joinable=
- verify!
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.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 117 117: def active? 118: @active != false 119: end
Returns the human-readable name of the adapter. Use mixed case - one can always use downcase if needed.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 49 49: def adapter_name 50: 'Abstract' 51: end
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 182 182: def create_savepoint 183: end
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 191 191: def current_savepoint_name 192: "active_record_#{open_transactions}" 193: end
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 174 174: def decrement_open_transactions 175: @open_transactions -= 1 176: end
Override to turn off referential integrity while executing &block.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 108 108: def disable_referential_integrity(&block) 109: yield 110: end
Disconnects from the database if already connected. Otherwise, this method does nothing.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 129 129: def disconnect! 130: @active = false 131: end
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 169 169: def increment_open_transactions 170: @open_transactions ||= 0 171: @open_transactions += 1 172: end
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 195 195: def log_info(sql, name, ms) 196: if @logger && @logger.debug? 197: name = '%s (%.1fms)' % [name || 'SQL', ms] 198: @logger.debug(format_log_entry(name, sql.squeeze(' '))) 199: end 200: end
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 165 165: def open_transactions 166: @open_transactions ||= 0 167: 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.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 89 89: def prefetch_primary_key?(table_name = nil) 90: false 91: end
Override to return the quoted table name. Defaults to column quoting.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 101 101: def quote_table_name(name) 102: quote_column_name(name) 103: 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.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 161 161: def raw_connection 162: @connection 163: end
Disconnects from the database if already connected, and establishes a new connection with the database.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 123 123: def reconnect! 124: @active = true 125: end
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 188 188: def release_savepoint 189: end
Returns true if its safe to reload the connection between requests for development mode.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 144 144: def requires_reloading? 145: true 146: 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.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 139 139: def reset! 140: # this should be overridden by concrete adapters 141: end
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 185 185: def rollback_to_savepoint 186: end
Does this adapter support using DISTINCT within COUNT? This is true for all adapters except sqlite.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 68 68: def supports_count_distinct? 69: true 70: 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.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 75 75: def supports_ddl_transactions? 76: false 77: end
Does this adapter support migrations? Backend specific, as the abstract adapter always returns false.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 55 55: def supports_migrations? 56: false 57: end
Can this adapter determine the primary key for tables not attached to an ActiveRecord class, such as join tables? Backend specific, as the abstract adapter always returns false.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 62 62: def supports_primary_key? 63: false 64: end
Does this adapter support savepoints? PostgreSQL and MySQL do, SQLite does not.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 81 81: def supports_savepoints? 82: false 83: end
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 178 178: def transaction_joinable=(joinable) 179: @transaction_joinable = joinable 180: 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.
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 151 151: def verify!(*ignored) 152: reconnect! unless active? 153: end
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 224 224: def format_log_entry(message, dump = nil) 225: if ActiveRecord::Base.colorize_logging 226: if @@row_even 227: @@row_even = false 228: message_color, dump_color = "4;36;1", "0;1" 229: else 230: @@row_even = true 231: message_color, dump_color = "4;35;1", "0" 232: end 233: 234: log_entry = " \e[#{message_color}m#{message}\e[0m " 235: log_entry << "\e[#{dump_color}m%#{String === dump ? 's' : 'p'}\e[0m" % dump if dump 236: log_entry 237: else 238: "%s %s" % [message, dump] 239: end 240: end
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# File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 203 203: def log(sql, name) 204: if block_given? 205: result = nil 206: ms = Benchmark.ms { result = yield } 207: @runtime += ms 208: log_info(sql, name, ms) 209: result 210: else 211: log_info(sql, name, 0) 212: nil 213: end 214: rescue Exception => e 215: # Log message and raise exception. 216: # Set last_verification to 0, so that connection gets verified 217: # upon reentering the request loop 218: @last_verification = 0 219: message = "#{e.class.name}: #{e.message}: #{sql}" 220: log_info(message, name, 0) 221: raise ActiveRecord::StatementInvalid, message 222: end