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.

Methods
Included Modules
Public Instance 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 117
117:       def active?
118:         @active != false
119:       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 49
49:       def adapter_name
50:         'Abstract'
51:       end
create_savepoint()
     # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 182
182:       def create_savepoint
183:       end
current_savepoint_name()
     # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 191
191:       def current_savepoint_name
192:         "active_record_#{open_transactions}"
193:       end
decrement_open_transactions()
     # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 174
174:       def decrement_open_transactions
175:         @open_transactions -= 1
176:       end
disable_referential_integrity() {|| ...}

Override to turn off referential integrity while executing &block.

     # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 108
108:       def disable_referential_integrity(&block)
109:         yield
110:       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 129
129:       def disconnect!
130:         @active = false
131:       end
increment_open_transactions()
     # 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
log_info(sql, name, ms)
     # 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
open_transactions()
     # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 165
165:       def open_transactions
166:         @open_transactions ||= 0
167:       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.

    # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 89
89:       def prefetch_primary_key?(table_name = nil)
90:         false
91:       end
quote_table_name(name)

Override to return the quoted table name. Defaults to column quoting.

     # 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
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.

     # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 161
161:       def raw_connection
162:         @connection
163:       end
reconnect!()

Disconnects from the database if already connected, and establishes a new connection with the database.

     # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 123
123:       def reconnect!
124:         @active = true
125:       end
release_savepoint()
     # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 188
188:       def release_savepoint
189:       end
requires_reloading?()

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

     # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 144
144:       def requires_reloading?
145:         true
146:       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 139
139:       def reset!
140:         # this should be overridden by concrete adapters
141:       end
rollback_to_savepoint()
     # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 185
185:       def rollback_to_savepoint
186:       end
supports_count_distinct?()

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

    # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 68
68:       def supports_count_distinct?
69:         true
70:       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.

    # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 75
75:       def supports_ddl_transactions?
76:         false
77:       end
supports_migrations?()

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

    # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 55
55:       def supports_migrations?
56:         false
57:       end
supports_primary_key?()

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.

    # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 62
62:       def supports_primary_key?
63:         false
64:       end
supports_savepoints?()

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

    # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 81
81:       def supports_savepoints?
82:         false
83:       end
transaction_joinable=(joinable)
     # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 178
178:       def transaction_joinable=(joinable)
179:         @transaction_joinable = joinable
180:       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.

     # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 151
151:       def verify!(*ignored)
152:         reconnect! unless active?
153:       end
Protected Instance methods
format_log_entry(message, dump = nil)
     # File activerecord/lib/active_record/connection_adapters/abstract_adapter.rb, line 230
230:         def format_log_entry(message, dump = nil)
231:           if ActiveRecord::Base.colorize_logging
232:             if @@row_even
233:               @@row_even = false
234:               message_color, dump_color = "4;36;1", "0;1"
235:             else
236:               @@row_even = true
237:               message_color, dump_color = "4;35;1", "0"
238:             end
239: 
240:             log_entry = "  \e[#{message_color}m#{message}\e[0m   "
241:             log_entry << "\e[#{dump_color}m%#{String === dump ? 's' : 'p'}\e[0m" % dump if dump
242:             log_entry
243:           else
244:             "%s  %s" % [message, dump]
245:           end
246:         end
log(sql, name) {|| ...}
     # 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 SystemExit, SignalException, NoMemoryError => e
215:           # Don't re-wrap these exceptions. They are probably not being caused by invalid
216:           # sql, but rather some external stimulus beyond the responsibilty of this code.
217:           # Additionaly, wrapping these exceptions with StatementInvalid would lead to
218:           #  meaningful loss of data, such as losing SystemExit#status.
219:           raise e
220:         rescue Exception => e
221:           # Log message and raise exception.
222:           # Set last_verification to 0, so that connection gets verified
223:           # upon reentering the request loop
224:           @last_verification = 0
225:           message = "#{e.class.name}: #{e.message}: #{sql}"
226:           log_info(message, name, 0)
227:           raise ActiveRecord::StatementInvalid, message
228:         end