instance method
transaction
Ruby on Rails 3.2.22.5
Since v2.2.3Signature
transaction(options = {})Runs the given block in a database transaction, and returns the result of the block.
Nested transactions support
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/5.0/en/savepoint.html Savepoints are supported by MySQL and PostgreSQL, but not SQLite3.
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_newis set, the block will be wrapped in a database savepoint acting as a sub-transaction.
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
Parameters
-
optionsopt = {}
Source
# File activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb, line 166
def transaction(options = {})
options.assert_valid_keys :requires_new, :joinable
last_transaction_joinable = defined?(@transaction_joinable) ? @transaction_joinable : nil
if options.has_key?(:joinable)
@transaction_joinable = options[:joinable]
else
@transaction_joinable = true
end
requires_new = options[:requires_new] || !last_transaction_joinable
transaction_open = false
@_current_transaction_records ||= []
begin
if block_given?
if requires_new || open_transactions == 0
if open_transactions == 0
begin_db_transaction
elsif requires_new
create_savepoint
end
increment_open_transactions
transaction_open = true
@_current_transaction_records.push([])
end
yield
end
rescue Exception => database_transaction_rollback
if transaction_open && !outside_transaction?
transaction_open = false
decrement_open_transactions
if open_transactions == 0
rollback_db_transaction
rollback_transaction_records(true)
else
rollback_to_savepoint
rollback_transaction_records(false)
end
end
raise unless database_transaction_rollback.is_a?(ActiveRecord::Rollback)
end
ensure
@transaction_joinable = last_transaction_joinable
if outside_transaction?
@open_transactions = 0
elsif transaction_open
decrement_open_transactions
begin
if open_transactions == 0
commit_db_transaction
commit_transaction_records
else
release_savepoint
save_point_records = @_current_transaction_records.pop
unless save_point_records.blank?
@_current_transaction_records.push([]) if @_current_transaction_records.empty?
@_current_transaction_records.last.concat(save_point_records)
end
end
rescue Exception => database_transaction_rollback
if open_transactions == 0
rollback_db_transaction
rollback_transaction_records(true)
else
rollback_to_savepoint
rollback_transaction_records(false)
end
raise
end
end
end
Defined in activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb line 166
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Defined in ActiveRecord::ConnectionAdapters::DatabaseStatements