diff options
Diffstat (limited to 'activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb')
-rw-r--r-- | activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb | 110 |
1 files changed, 99 insertions, 11 deletions
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb index 189c6c7b5a..08601da00a 100644 --- a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb +++ b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb @@ -53,36 +53,124 @@ module ActiveRecord def delete(sql, name = nil) delete_sql(sql, name) end + + # Checks whether there is currently no transaction active. This is done + # by querying the database driver, and does not use the transaction + # house-keeping information recorded by #increment_open_transactions and + # friends. + # + # Returns true if there is no transaction active, false if there is a + # transaction active, and nil if this information is unknown. + # + # Not all adapters supports transaction state introspection. Currently, + # only the PostgreSQL adapter supports this. + def outside_transaction? + nil + end + + # 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: + # http://dev.mysql.com/doc/refman/5.0/en/savepoints.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_new+ is 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 + def transaction(options = {}) + options.assert_valid_keys :requires_new, :joinable + + last_transaction_joinable = @transaction_joinable + if options.has_key?(:joinable) + @transaction_joinable = options[:joinable] + else + @transaction_joinable = true + end + requires_new = options[:requires_new] || !last_transaction_joinable - # Wrap a block in a transaction. Returns result of block. - def transaction(start_db_transaction = true) transaction_open = false begin if block_given? - if start_db_transaction - begin_db_transaction + 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 end yield end rescue Exception => database_transaction_rollback - if transaction_open + if transaction_open && !outside_transaction? transaction_open = false - rollback_db_transaction + decrement_open_transactions + if open_transactions == 0 + rollback_db_transaction + else + rollback_to_savepoint + end end - raise unless database_transaction_rollback.is_a? ActiveRecord::Rollback + raise unless database_transaction_rollback.is_a?(ActiveRecord::Rollback) end ensure - if transaction_open + @transaction_joinable = last_transaction_joinable + + if outside_transaction? + @open_transactions = 0 + elsif transaction_open + decrement_open_transactions begin - commit_db_transaction + if open_transactions == 0 + commit_db_transaction + else + release_savepoint + end rescue Exception => database_transaction_rollback - rollback_db_transaction + if open_transactions == 0 + rollback_db_transaction + else + rollback_to_savepoint + end raise end end end - + # Begins the transaction (and turns off auto-committing). def begin_db_transaction() end |