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 | 101 |
1 files changed, 92 insertions, 9 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..cecbc6b3ac 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 +53,119 @@ 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 - # Wrap a block in a transaction. Returns result of block. - def transaction(start_db_transaction = true) + # 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 +start_db_transaction+ is set to true, then the block will + # be run inside a new database savepoint, effectively making the block + # a sub-transaction. + # - If the #transactional_fixtures attribute is set to true, then the first + # nested call to #transaction will create a new savepoint instead of + # doing nothing. This makes it possible for toplevel transactions in unit + # tests to behave like real transactions, even though a database + # transaction has already been opened. + # + # === 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(true) do # CREATE SAVEPOINT rails_savepoint_1 + # Model.connection.create_table(...) + # # rails_savepoint_1 now automatically released + # end # RELEASE savepoint rails_savepoint_1 <--- BOOM! database error! + # end + def transaction(start_db_transaction = false) + start_db_transaction ||= open_transactions == 0 || (open_transactions == 1 && transactional_fixtures) transaction_open = false begin if block_given? if start_db_transaction - begin_db_transaction + if open_transactions == 0 + begin_db_transaction + else + 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 end ensure - if transaction_open + 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 |