Module: ActiveRecord::ConnectionAdapters::DatabaseStatements

Included in:
AbstractAdapter
Defined in:
lib/active_record/connection_adapters/abstract/database_statements.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Instance Attribute Details

#transaction_managerObject (readonly)

:nodoc:



348
349
350
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 348

def transaction_manager
  @transaction_manager
end

Instance Method Details

#add_transaction_record(record, ensure_finalize = true) ⇒ Object

Register a record with the current transaction so that its after_commit and after_rollback callbacks can be called.



388
389
390
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 388

def add_transaction_record(record, ensure_finalize = true)
  current_transaction.add_record(record, ensure_finalize)
end

#begin_db_transactionObject

Begins the transaction (and turns off auto-committing).



393
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 393

def begin_db_transaction()    end

#begin_isolated_db_transaction(isolation) ⇒ Object

Begins the transaction with the isolation level set. Raises an error by default; adapters that support setting the isolation level should implement this method.



407
408
409
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 407

def begin_isolated_db_transaction(isolation)
  raise ActiveRecord::TransactionIsolationError, "adapter does not support setting transaction isolation"
end

#cacheable_query(klass, arel) ⇒ Object

This is used in the StatementCache object. It returns an object that can be used to query the database repeatedly.



54
55
56
57
58
59
60
61
62
63
64
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 54

def cacheable_query(klass, arel) # :nodoc:
  if prepared_statements
    sql, binds = visitor.compile(arel.ast, collector)
    query = klass.query(sql)
  else
    collector = klass.partial_query_collector
    parts, binds = visitor.compile(arel.ast, collector)
    query = klass.partial_query(parts)
  end
  [query, binds]
end

#commit_db_transactionObject

Commits the transaction (and turns on auto-committing).



412
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 412

def commit_db_transaction()   end

#default_sequence_name(table, column) ⇒ Object



434
435
436
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 434

def default_sequence_name(table, column)
  nil
end

#delete(arel, name = nil, binds = []) ⇒ Object

Executes the delete statement and returns the number of rows affected.



204
205
206
207
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 204

def delete(arel, name = nil, binds = [])
  sql, binds = to_sql_and_binds(arel, binds)
  exec_delete(sql, name, binds)
end

#empty_insert_statement_value(primary_key = nil) ⇒ Object



466
467
468
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 466

def empty_insert_statement_value(primary_key = nil)
  "DEFAULT VALUES"
end

#exec_delete(sql, name = nil, binds = []) ⇒ Object

Executes delete sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.



159
160
161
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 159

def exec_delete(sql, name = nil, binds = [])
  internal_exec_query(sql, name, binds)
end

#exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil, returning: nil) ⇒ Object

Executes insert sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement. Some adapters support the ‘returning` keyword argument which allows to control the result of the query: `nil` is the default value and maintains default behavior. If an array of column names is passed - the result will contain values of the specified columns from the inserted row.



151
152
153
154
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 151

def exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil, returning: nil)
  sql, binds = sql_for_insert(sql, pk, binds, returning)
  internal_exec_query(sql, name, binds)
end

#exec_insert_all(sql, name) ⇒ Object

:nodoc:



170
171
172
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 170

def exec_insert_all(sql, name) # :nodoc:
  internal_exec_query(sql, name)
end

#exec_query(sql, name = "SQL", binds = [], prepare: false) ⇒ Object

Executes sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.

Note: the query is assumed to have side effects and the query cache will be cleared. If the query is read-only, consider using #select_all instead.



141
142
143
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 141

def exec_query(sql, name = "SQL", binds = [], prepare: false)
  internal_exec_query(sql, name, binds, prepare: prepare)
end

#exec_restart_db_transactionObject

:nodoc:



428
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 428

def exec_restart_db_transaction() end

#exec_rollback_db_transactionObject

:nodoc:



422
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 422

def exec_rollback_db_transaction() end

#exec_update(sql, name = nil, binds = []) ⇒ Object

Executes update sql statement in the context of this connection using binds as the bind substitutes. name is logged along with the executed sql statement.



166
167
168
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 166

def exec_update(sql, name = nil, binds = [])
  internal_exec_query(sql, name, binds)
end

#execute(sql, name = nil, allow_retry: false) ⇒ Object

Executes the SQL statement in the context of this connection and returns the raw result from the connection adapter.

Setting allow_retry to true causes the db to reconnect and retry executing the SQL statement in case of a connection-related exception. This option should only be enabled for known idempotent queries.

Note: the query is assumed to have side effects and the query cache will be cleared. If the query is read-only, consider using #select_all instead.

Note: depending on your database connector, the result returned by this method may be manually memory managed. Consider using #exec_query wrapper instead.



130
131
132
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 130

def execute(sql, name = nil, allow_retry: false)
  internal_execute(sql, name, allow_retry: allow_retry)
end

#explain(arel, binds = [], options = []) ⇒ Object

:nodoc:

Raises:

  • (NotImplementedError)


174
175
176
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 174

def explain(arel, binds = [], options = []) # :nodoc:
  raise NotImplementedError
end

#high_precision_current_timestampObject

Returns an Arel SQL literal for the CURRENT_TIMESTAMP for usage with arbitrary precision date/time columns.

Adapters supporting datetime with precision should override this to provide as much precision as is available.



504
505
506
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 504

def high_precision_current_timestamp
  HIGH_PRECISION_CURRENT_TIMESTAMP
end

#initializeObject



6
7
8
9
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 6

def initialize
  super
  reset_transaction
end

#insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [], returning: nil) ⇒ Object Also known as: create

Executes an INSERT query and returns the new record’s ID

id_value will be returned unless the value is nil, in which case the database will attempt to calculate the last inserted id and return that value.

If the next id was calculated in advance (as in Oracle), it should be passed in as id_value. Some adapters support the ‘returning` keyword argument which allows defining the return value of the method: `nil` is the default value and maintains default behavior. If an array of column names is passed - an array of is returned from the method representing values of the specified columns from the inserted row.



189
190
191
192
193
194
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 189

def insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [], returning: nil)
  sql, binds = to_sql_and_binds(arel, binds)
  value = exec_insert(sql, name, binds, pk, sequence_name, returning: returning)
  return id_value if id_value
  returning.nil? ? last_inserted_id(value) : returning_column_values(value)
end

#insert_fixture(fixture, table_name) ⇒ Object

Inserts the given fixture into the table. Overridden in adapters that require something beyond a simple insert (e.g. Oracle). Most of adapters should implement insert_fixtures_set that leverages bulk SQL insert. We keep this method to provide fallback for databases like SQLite that do not support bulk inserts.



448
449
450
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 448

def insert_fixture(fixture, table_name)
  execute(build_fixture_sql(Array.wrap(fixture), table_name), "Fixture Insert")
end

#insert_fixtures_set(fixture_set, tables_to_delete = []) ⇒ Object



452
453
454
455
456
457
458
459
460
461
462
463
464
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 452

def insert_fixtures_set(fixture_set, tables_to_delete = [])
  fixture_inserts = build_fixture_statements(fixture_set)
  table_deletes = tables_to_delete.map { |table| "DELETE FROM #{quote_table_name(table)}" }
  statements = table_deletes + fixture_inserts

  with_multi_statements do
    disable_referential_integrity do
      transaction(requires_new: true) do
        execute_batch(statements, "Fixtures Load")
      end
    end
  end
end

#internal_exec_query(sql, name = "SQL", binds = [], prepare: false, async: false) ⇒ Object

:nodoc:

Raises:

  • (NotImplementedError)


508
509
510
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 508

def internal_exec_query(sql, name = "SQL", binds = [], prepare: false, async: false) # :nodoc:
  raise NotImplementedError
end

#mark_transaction_written_if_write(sql) ⇒ Object

:nodoc:



355
356
357
358
359
360
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 355

def mark_transaction_written_if_write(sql) # :nodoc:
  transaction = current_transaction
  if transaction.open?
    transaction.written ||= write_query?(sql)
  end
end

#query(sql, name = nil) ⇒ Object

:nodoc:



107
108
109
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 107

def query(sql, name = nil) # :nodoc:
  internal_exec_query(sql, name).rows
end

#query_value(sql, name = nil) ⇒ Object

:nodoc:



99
100
101
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 99

def query_value(sql, name = nil) # :nodoc:
  single_value_from_rows(query(sql, name))
end

#query_values(sql, name = nil) ⇒ Object

:nodoc:



103
104
105
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 103

def query_values(sql, name = nil) # :nodoc:
  query(sql, name).map(&:first)
end

#reset_sequence!(table, column, sequence = nil) ⇒ Object

Set the sequence to the max value of the table’s column.



439
440
441
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 439

def reset_sequence!(table, column, sequence = nil)
  # Do nothing by default. Implement for PostgreSQL, Oracle, ...
end

#reset_transaction(restore: false) ⇒ Object

:nodoc:



366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 366

def reset_transaction(restore: false) # :nodoc:
  # Store the existing transaction state to the side
  old_state = @transaction_manager if restore && @transaction_manager&.restorable?

  @transaction_manager = ConnectionAdapters::TransactionManager.new(self)

  if block_given?
    # Reconfigure the connection without any transaction state in the way
    result = yield

    # Now the connection's fully established, we can swap back
    if old_state
      @transaction_manager = old_state
      @transaction_manager.restore_transactions
    end

    result
  end
end

#restart_db_transactionObject



424
425
426
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 424

def restart_db_transaction
  exec_restart_db_transaction
end

#rollback_db_transactionObject

Rolls back the transaction (and turns on auto-committing). Must be done if the transaction block raises an exception or returns false.



416
417
418
419
420
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 416

def rollback_db_transaction
  exec_rollback_db_transaction
rescue ActiveRecord::ConnectionNotEstablished, ActiveRecord::ConnectionFailed
  # Connection's gone; that counts as a rollback
end

#rollback_to_savepoint(name = nil) ⇒ Object



430
431
432
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 430

def rollback_to_savepoint(name = nil)
  exec_rollback_to_savepoint(name)
end

#sanitize_limit(limit) ⇒ Object

Sanitizes the given LIMIT parameter in order to prevent SQL injection.

The limit may be anything that can evaluate to a string via #to_s. It should look like an integer, or an Arel SQL literal.

Returns Integer and Arel::Nodes::SqlLiteral limits as is.



476
477
478
479
480
481
482
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 476

def sanitize_limit(limit)
  if limit.is_a?(Integer) || limit.is_a?(Arel::Nodes::SqlLiteral)
    limit
  else
    Integer(limit)
  end
end

#select_all(arel, name = nil, binds = [], preparable: nil, async: false) ⇒ Object

Returns an ActiveRecord::Result instance.



67
68
69
70
71
72
73
74
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 67

def select_all(arel, name = nil, binds = [], preparable: nil, async: false)
  arel = arel_from_relation(arel)
  sql, binds, preparable = to_sql_and_binds(arel, binds, preparable)

  select(sql, name, binds, prepare: prepared_statements && preparable, async: async && FutureResult::SelectAll)
rescue ::RangeError
  ActiveRecord::Result.empty(async: async)
end

#select_one(arel, name = nil, binds = [], async: false) ⇒ Object

Returns a record hash with the column names as keys and column values as values.



78
79
80
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 78

def select_one(arel, name = nil, binds = [], async: false)
  select_all(arel, name, binds, async: async).then(&:first)
end

#select_rows(arel, name = nil, binds = [], async: false) ⇒ Object

Returns an array of arrays containing the field values. Order is the same as that returned by columns.



95
96
97
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 95

def select_rows(arel, name = nil, binds = [], async: false)
  select_all(arel, name, binds, async: async).then(&:rows)
end

#select_value(arel, name = nil, binds = [], async: false) ⇒ Object

Returns a single value from a record



83
84
85
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 83

def select_value(arel, name = nil, binds = [], async: false)
  select_rows(arel, name, binds, async: async).then { |rows| single_value_from_rows(rows) }
end

#select_values(arel, name = nil, binds = []) ⇒ Object

Returns an array of the values of the first column in a select:

select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]


89
90
91
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 89

def select_values(arel, name = nil, binds = [])
  select_rows(arel, name, binds).map(&:first)
end

#to_sql(arel_or_sql_string, binds = []) ⇒ Object

Converts an arel AST to SQL



12
13
14
15
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 12

def to_sql(arel_or_sql_string, binds = [])
  sql, _ = to_sql_and_binds(arel_or_sql_string, binds)
  sql
end

#transaction(requires_new: nil, isolation: nil, joinable: true, &block) ⇒ Object

Runs the given block in a database transaction, and returns the result of the block.

Nested transactions support

#transaction calls can be nested. By default, this makes all database statements in the nested transaction block become part of the parent transaction. For example, the following behavior may be surprising:

ActiveRecord::Base.transaction do
  Post.create(title: 'first')
  ActiveRecord::Base.transaction do
    Post.create(title: 'second')
    raise ActiveRecord::Rollback
  end
end

This creates both “first” and “second” posts. Reason is the ActiveRecord::Rollback exception in the nested block does not issue a ROLLBACK. Since these exceptions are captured in transaction blocks, the parent block does not see it and the real transaction is committed.

Most databases don’t support true nested transactions. At the time of writing, the only database that supports true nested transactions that we’re aware of, is MS-SQL.

In order to get around this problem, #transaction will emulate the effect of nested transactions, by using savepoints: dev.mysql.com/doc/refman/en/savepoint.html.

It is safe to call this method if a database transaction is already open, i.e. if #transaction is called within another #transaction block. In case of a nested call, #transaction will behave as follows:

  • The block will be run without doing anything. All database statements that happen within the block are effectively appended to the already open database transaction.

  • However, if :requires_new is set, the block will be wrapped in a database savepoint acting as a sub-transaction.

In order to get a ROLLBACK for the nested transaction you may ask for a real sub-transaction by passing requires_new: true. If anything goes wrong, the database rolls back to the beginning of the sub-transaction without rolling back the parent transaction. If we add it to the previous example:

ActiveRecord::Base.transaction do
  Post.create(title: 'first')
  ActiveRecord::Base.transaction(requires_new: true) do
    Post.create(title: 'second')
    raise ActiveRecord::Rollback
  end
end

only post with title “first” is created.

See ActiveRecord::Transactions to learn more.

Caveats

MySQL doesn’t support DDL transactions. If you perform a DDL operation, then any created savepoints will be automatically released. For example, if you’ve created a savepoint, then you execute a CREATE TABLE statement, then the savepoint that was created will be automatically released.

This means that, on MySQL, you shouldn’t execute DDL operations inside a #transaction call that you know might create a savepoint. Otherwise, #transaction will raise exceptions when it tries to release the already-automatically-released savepoints:

Model.connection.transaction do  # BEGIN
  Model.connection.transaction(requires_new: true) do  # CREATE SAVEPOINT active_record_1
    Model.connection.create_table(...)
    # active_record_1 now automatically released
  end  # RELEASE SAVEPOINT active_record_1  <--- BOOM! database error!
end

Transaction isolation

If your database supports setting the isolation level for a transaction, you can set it like so:

Post.transaction(isolation: :serializable) do
  # ...
end

Valid isolation levels are:

  • :read_uncommitted

  • :read_committed

  • :repeatable_read

  • :serializable

You should consult the documentation for your database to understand the semantics of these different levels:

An ActiveRecord::TransactionIsolationError will be raised if:

  • The adapter does not support setting the isolation level

  • You are joining an existing open transaction

  • You are creating a nested (savepoint) transaction

The mysql2, trilogy, and postgresql adapters support setting the transaction isolation level.

:args: (requires_new: nil, isolation: nil, &block)


335
336
337
338
339
340
341
342
343
344
345
346
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 335

def transaction(requires_new: nil, isolation: nil, joinable: true, &block)
  if !requires_new && current_transaction.joinable?
    if isolation
      raise ActiveRecord::TransactionIsolationError, "cannot set isolation when joining a transaction"
    end
    yield
  else
    transaction_manager.within_new_transaction(isolation: isolation, joinable: joinable, &block)
  end
rescue ActiveRecord::Rollback
  # rollbacks are silently swallowed
end

#transaction_isolation_levelsObject



395
396
397
398
399
400
401
402
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 395

def transaction_isolation_levels
  {
    read_uncommitted: "READ UNCOMMITTED",
    read_committed:   "READ COMMITTED",
    repeatable_read:  "REPEATABLE READ",
    serializable:     "SERIALIZABLE"
  }
end

#transaction_open?Boolean

Returns:

  • (Boolean)


362
363
364
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 362

def transaction_open?
  current_transaction.open?
end

#truncate(table_name, name = nil) ⇒ Object

Executes the truncate statement.



210
211
212
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 210

def truncate(table_name, name = nil)
  execute(build_truncate_statement(table_name), name)
end

#truncate_tables(*table_names) ⇒ Object

:nodoc:



214
215
216
217
218
219
220
221
222
223
224
225
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 214

def truncate_tables(*table_names) # :nodoc:
  table_names -= [schema_migration.table_name, .table_name]

  return if table_names.empty?

  with_multi_statements do
    disable_referential_integrity do
      statements = build_truncate_statements(table_names)
      execute_batch(statements, "Truncate Tables")
    end
  end
end

#update(arel, name = nil, binds = []) ⇒ Object

Executes the update statement and returns the number of rows affected.



198
199
200
201
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 198

def update(arel, name = nil, binds = [])
  sql, binds = to_sql_and_binds(arel, binds)
  exec_update(sql, name, binds)
end

#with_yaml_fallback(value) ⇒ Object

Fixture value is quoted by Arel, however scalar values are not quotable. In this case we want to convert the column value to YAML.



487
488
489
490
491
492
493
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 487

def with_yaml_fallback(value) # :nodoc:
  if value.is_a?(Hash) || value.is_a?(Array)
    YAML.dump(value)
  else
    value
  end
end

#write_query?(sql) ⇒ Boolean

Determines whether the SQL statement is a write query.

Returns:

  • (Boolean)

Raises:

  • (NotImplementedError)


112
113
114
# File 'lib/active_record/connection_adapters/abstract/database_statements.rb', line 112

def write_query?(sql)
  raise NotImplementedError
end