Methods
- add_transaction_record
- begin_db_transaction
- begin_isolated_db_transaction
- commit_db_transaction
- create
- default_sequence_name
- delete
- empty_insert_statement_value
- exec_delete
- exec_insert
- exec_query
- exec_update
- execute
- high_precision_current_timestamp
- insert
- insert_fixture
- insert_fixtures_set
- new
- reset_isolation_level
- reset_sequence!
- restart_db_transaction
- rollback_db_transaction
- rollback_to_savepoint
- sanitize_limit
- select_all
- select_one
- select_rows
- select_value
- select_values
- to_sql
- transaction
- transaction_isolation_levels
- transaction_open?
- truncate
- update
- write_query?
Class Public methods
new()
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 6
def initialize
super
reset_transaction
end
π See on GitHub
Instance Public methods
add_transaction_record(record, ensure_finalize = true)
Register a record with the current transaction so that its after_commit and after_rollback callbacks can be called.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 405
def add_transaction_record(record, ensure_finalize = true)
current_transaction.add_record(record, ensure_finalize)
end
π See on GitHub
begin_db_transaction()
Begins the transaction (and turns off auto-committing).
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 410
def begin_db_transaction() end
π See on GitHub
begin_isolated_db_transaction(isolation)
Begins the transaction with the isolation level set. Raises an error by default; adapters that support setting the isolation level should implement this method.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 432
def begin_isolated_db_transaction(isolation)
raise ActiveRecord::TransactionIsolationError, "adapter does not support setting transaction isolation"
end
π See on GitHub
commit_db_transaction()
Commits the transaction (and turns on auto-committing).
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 446
def commit_db_transaction() end
π See on GitHub
create(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [], returning: nil)
default_sequence_name(table, column)
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 468
def default_sequence_name(table, column)
nil
end
π See on GitHub
delete(arel, name = nil, binds = [])
Executes the delete statement and returns the number of rows affected.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 212
def delete(arel, name = nil, binds = [])
sql, binds = to_sql_and_binds(arel, binds)
exec_delete(sql, name, binds)
end
π See on GitHub
empty_insert_statement_value(primary_key = nil)
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 498
def empty_insert_statement_value(primary_key = nil)
"DEFAULT VALUES"
end
π See on GitHub
exec_delete(sql, name = nil, binds = [])
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.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 165
def exec_delete(sql, name = nil, binds = [])
affected_rows(internal_execute(sql, name, binds))
end
π See on GitHub
exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil, returning: nil)
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 βreturning` 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.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 157
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
π See on GitHub
exec_query(sql, name = "SQL", binds = [], prepare: false)
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.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 147
def exec_query(sql, name = "SQL", binds = [], prepare: false)
internal_exec_query(sql, name, binds, prepare: prepare)
end
π See on GitHub
exec_update(sql, name = nil, binds = [])
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.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 172
def exec_update(sql, name = nil, binds = [])
affected_rows(internal_execute(sql, name, binds))
end
π See on GitHub
execute(sql, name = nil, allow_retry: false)
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.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 136
def execute(sql, name = nil, allow_retry: false)
internal_execute(sql, name, allow_retry: allow_retry)
end
π See on GitHub
high_precision_current_timestamp()
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.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 536
def high_precision_current_timestamp
HIGH_PRECISION_CURRENT_TIMESTAMP
end
π See on GitHub
insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [], returning: nil)
Executes an INSERT query and returns the new recordβs 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 βreturning` 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.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 195
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 returning_column_values(value) unless returning.nil?
id_value || last_inserted_id(value)
end
π See on GitHub
insert_fixture(fixture, table_name)
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.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 482
def insert_fixture(fixture, table_name)
execute(build_fixture_sql(Array.wrap(fixture), table_name), "Fixture Insert")
end
π See on GitHub
insert_fixtures_set(fixture_set, tables_to_delete = [])
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 486
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
transaction(requires_new: true) do
disable_referential_integrity do
execute_batch(statements, "Fixtures Load")
end
end
end
π See on GitHub
reset_isolation_level()
Hook point called after an isolated DB transaction is committed or rolled back. Most adapters donβt need to implement anything because the isolation level is set on a per transaction basis. But some databases like SQLite set it on a per connection level and need to explicitly reset it after commit or rollback.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 442
def reset_isolation_level
end
π See on GitHub
reset_sequence!(table, column, sequence = nil)
Set the sequence to the max value of the tableβs column.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 473
def reset_sequence!(table, column, sequence = nil)
# Do nothing by default. Implement for PostgreSQL, Oracle, ...
end
π See on GitHub
restart_db_transaction()
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 458
def restart_db_transaction
exec_restart_db_transaction
end
π See on GitHub
rollback_db_transaction()
Rolls back the transaction (and turns on auto-committing). Must be done if the transaction block raises an exception or returns false.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 450
def rollback_db_transaction
exec_rollback_db_transaction
rescue ActiveRecord::ConnectionNotEstablished, ActiveRecord::ConnectionFailed
# Connection's gone; that counts as a rollback
end
π See on GitHub
rollback_to_savepoint(name = nil)
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 464
def rollback_to_savepoint(name = nil)
exec_rollback_to_savepoint(name)
end
π See on GitHub
sanitize_limit(limit)
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.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 508
def sanitize_limit(limit)
if limit.is_a?(Integer) || limit.is_a?(Arel::Nodes::SqlLiteral)
limit
else
Integer(limit)
end
end
π See on GitHub
select_all(arel, name = nil, binds = [], preparable: nil, async: false, allow_retry: false)
Returns an ActiveRecord::Result
instance.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 69
def select_all(arel, name = nil, binds = [], preparable: nil, async: false, allow_retry: false)
arel = arel_from_relation(arel)
sql, binds, preparable, allow_retry = to_sql_and_binds(arel, binds, preparable, allow_retry)
select(sql, name, binds,
prepare: prepared_statements && preparable,
async: async && FutureResult::SelectAll,
allow_retry: allow_retry
)
rescue ::RangeError
ActiveRecord::Result.empty(async: async)
end
π See on GitHub
select_one(arel, name = nil, binds = [], async: false)
Returns a record hash with the column names as keys and column values as values.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 84
def select_one(arel, name = nil, binds = [], async: false)
select_all(arel, name, binds, async: async).then(&:first)
end
π See on GitHub
select_rows(arel, name = nil, binds = [], async: false)
Returns an array of arrays containing the field values. Order is the same as that returned by columns
.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 101
def select_rows(arel, name = nil, binds = [], async: false)
select_all(arel, name, binds, async: async).then(&:rows)
end
π See on GitHub
select_value(arel, name = nil, binds = [], async: false)
Returns a single value from a record
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 89
def select_value(arel, name = nil, binds = [], async: false)
select_rows(arel, name, binds, async: async).then { |rows| single_value_from_rows(rows) }
end
π See on GitHub
select_values(arel, name = nil, binds = [])
Returns an array of the values of the first column in a select:
select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 95
def select_values(arel, name = nil, binds = [])
select_rows(arel, name, binds).map(&:first)
end
π See on GitHub
to_sql(arel_or_sql_string, binds = [])
Converts an arel AST to SQL
π Source code
# File activerecord/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
π See on GitHub
transaction(requires_new: nil, isolation: nil, &block)
Runs the given block in a database transaction, and returns the result of the block.
Transaction
callbacks
transaction
yields an ActiveRecord::Transaction
object on which it is possible to register callback:
ActiveRecord::Base.transaction do |transaction|
transaction.before_commit { puts "before commit!" }
transaction.after_commit { puts "after commit!" }
transaction.after_rollback { puts "after rollback!" }
end
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 βfirstβ and βsecondβ 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 donβt support true nested transactions. At the time of writing, the only database that supports true nested transactions that weβre 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 βfirstβ is created.
See ActiveRecord::Transactions
to learn more.
Caveats
MySQL
doesnβt support DDL transactions. If you perform a DDL operation, then any created savepoints will be automatically released. For example, if youβve 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 shouldnβt 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.lease_connection.transaction do # BEGIN
Model.lease_connection.transaction(requires_new: true) do # CREATE SAVEPOINT active_record_1
Model.lease_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.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 352
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 current_transaction.user_transaction
else
within_new_transaction(isolation: isolation, joinable: joinable, &block)
end
rescue ActiveRecord::Rollback
# rollbacks are silently swallowed
end
π See on GitHub
transaction_isolation_levels()
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 420
def transaction_isolation_levels
{
read_uncommitted: "READ UNCOMMITTED",
read_committed: "READ COMMITTED",
repeatable_read: "REPEATABLE READ",
serializable: "SERIALIZABLE"
}
end
π See on GitHub
transaction_open?()
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 379
def transaction_open?
current_transaction.open?
end
π See on GitHub
truncate(table_name, name = nil)
Executes the truncate statement.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 218
def truncate(table_name, name = nil)
execute(build_truncate_statement(table_name), name)
end
π See on GitHub
update(arel, name = nil, binds = [])
Executes the update statement and returns the number of rows affected.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 206
def update(arel, name = nil, binds = [])
sql, binds = to_sql_and_binds(arel, binds)
exec_update(sql, name, binds)
end
π See on GitHub
write_query?(sql)
Determines whether the SQL statement is a write query.
π Source code
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 118
def write_query?(sql)
raise NotImplementedError
end
π See on GitHub