--- /dev/null
+require 'thread'
+
+module ActiveRecord
+ # See ActiveRecord::Transactions::ClassMethods for documentation.
+ module Transactions
+ class TransactionError < ActiveRecordError # :nodoc:
+ end
+
+ def self.included(base)
+ base.extend(ClassMethods)
+
+ base.class_eval do
+ [:destroy, :save, :save!].each do |method|
+ alias_method_chain method, :transactions
+ end
+ end
+ end
+
+ # Transactions are protective blocks where SQL statements are only permanent
+ # if they can all succeed as one atomic action. The classic example is a
+ # transfer between two accounts where you can only have a deposit if the
+ # withdrawal succeeded and vice versa. Transactions enforce the integrity of
+ # the database and guard the data against program errors or database
+ # break-downs. So basically you should use transaction blocks whenever you
+ # have a number of statements that must be executed together or not at all.
+ # Example:
+ #
+ # ActiveRecord::Base.transaction do
+ # david.withdrawal(100)
+ # mary.deposit(100)
+ # end
+ #
+ # This example will only take money from David and give to Mary if neither
+ # +withdrawal+ nor +deposit+ raises an exception. Exceptions will force a
+ # ROLLBACK that returns the database to the state before the transaction was
+ # begun. Be aware, though, that the objects will _not_ have their instance
+ # data returned to their pre-transactional state.
+ #
+ # == Different Active Record classes in a single transaction
+ #
+ # Though the transaction class method is called on some Active Record class,
+ # the objects within the transaction block need not all be instances of
+ # that class. This is because transactions are per-database connection, not
+ # per-model.
+ #
+ # In this example a <tt>Balance</tt> record is transactionally saved even
+ # though <tt>transaction</tt> is called on the <tt>Account</tt> class:
+ #
+ # Account.transaction do
+ # balance.save!
+ # account.save!
+ # end
+ #
+ # Note that the +transaction+ method is also available as a model instance
+ # method. For example, you can also do this:
+ #
+ # balance.transaction do
+ # balance.save!
+ # account.save!
+ # end
+ #
+ # == Transactions are not distributed across database connections
+ #
+ # A transaction acts on a single database connection. If you have
+ # multiple class-specific databases, the transaction will not protect
+ # interaction among them. One workaround is to begin a transaction
+ # on each class whose models you alter:
+ #
+ # Student.transaction do
+ # Course.transaction do
+ # course.enroll(student)
+ # student.units += course.units
+ # end
+ # end
+ #
+ # This is a poor solution, but full distributed transactions are beyond
+ # the scope of Active Record.
+ #
+ # == Save and destroy are automatically wrapped in a transaction
+ #
+ # Both Base#save and Base#destroy come wrapped in a transaction that ensures
+ # that whatever you do in validations or callbacks will happen under the
+ # protected cover of a transaction. So you can use validations to check for
+ # values that the transaction depends on or you can raise exceptions in the
+ # callbacks to rollback, including <tt>after_*</tt> callbacks.
+ #
+ # == Exception handling and rolling back
+ #
+ # Also have in mind that exceptions thrown within a transaction block will
+ # be propagated (after triggering the ROLLBACK), so you should be ready to
+ # catch those in your application code.
+ #
+ # One exception is the ActiveRecord::Rollback exception, which will trigger
+ # a ROLLBACK when raised, but not be re-raised by the transaction block.
+ #
+ # *Warning*: one should not catch ActiveRecord::StatementInvalid exceptions
+ # inside a transaction block. StatementInvalid exceptions indicate that an
+ # error occurred at the database level, for example when a unique constraint
+ # is violated. On some database systems, such as PostgreSQL, database errors
+ # inside a transaction causes the entire transaction to become unusable
+ # until it's restarted from the beginning. Here is an example which
+ # demonstrates the problem:
+ #
+ # # Suppose that we have a Number model with a unique column called 'i'.
+ # Number.transaction do
+ # Number.create(:i => 0)
+ # begin
+ # # This will raise a unique constraint error...
+ # Number.create(:i => 0)
+ # rescue ActiveRecord::StatementInvalid
+ # # ...which we ignore.
+ # end
+ #
+ # # On PostgreSQL, the transaction is now unusable. The following
+ # # statement will cause a PostgreSQL error, even though the unique
+ # # constraint is no longer violated:
+ # Number.create(:i => 1)
+ # # => "PGError: ERROR: current transaction is aborted, commands
+ # # ignored until end of transaction block"
+ # end
+ #
+ # One should restart the entire transaction if a StatementError occurred.
+ #
+ # == Nested transactions
+ #
+ # #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:
+ #
+ # User.transaction do
+ # User.create(:username => 'Kotori')
+ # User.transaction do
+ # User.create(:username => 'Nemu')
+ # raise ActiveRecord::Rollback
+ # end
+ # end
+ #
+ # User.find(:all) # => empty
+ #
+ # It is also possible to requires a sub-transaction by passing
+ # <tt>:requires_new => true</tt>. If anything goes wrong, the
+ # database rolls back to the beginning of the sub-transaction
+ # without rolling back the parent transaction. For example:
+ #
+ # User.transaction do
+ # User.create(:username => 'Kotori')
+ # User.transaction(:requires_new => true) do
+ # User.create(:username => 'Nemu')
+ # raise ActiveRecord::Rollback
+ # end
+ # end
+ #
+ # User.find(:all) # => Returns only Kotori
+ #
+ # Most databases don't support true nested transactions. At the time of
+ # writing, the only database that we're aware of that supports true nested
+ # transactions, is MS-SQL. Because of this, Active Record emulates nested
+ # transactions by using savepoints. See
+ # http://dev.mysql.com/doc/refman/5.0/en/savepoints.html
+ # for more information about savepoints.
+ #
+ # === Caveats
+ #
+ # If you're on MySQL, then do not use DDL operations in nested transactions
+ # blocks that are emulated with savepoints. That is, do not execute statements
+ # like 'CREATE TABLE' inside such blocks. This is because MySQL automatically
+ # releases all savepoints upon executing a DDL operation. When #transaction
+ # is finished and tries to release the savepoint it created earlier, a
+ # database error will occur because the savepoint has already been
+ # automatically released. The following example demonstrates the problem:
+ #
+ # 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
+ module ClassMethods
+ # See ActiveRecord::Transactions::ClassMethods for detailed documentation.
+ def transaction(options = {}, &block)
+ # See the ConnectionAdapters::DatabaseStatements#transaction API docs.
+ connection.transaction(options, &block)
+ end
+ end
+
+ # See ActiveRecord::Transactions::ClassMethods for detailed documentation.
+ def transaction(&block)
+ self.class.transaction(&block)
+ end
+
+ def destroy_with_transactions #:nodoc:
+ with_transaction_returning_status(:destroy_without_transactions)
+ end
+
+ def save_with_transactions(perform_validation = true) #:nodoc:
+ rollback_active_record_state! { with_transaction_returning_status(:save_without_transactions, perform_validation) }
+ end
+
+ def save_with_transactions! #:nodoc:
+ rollback_active_record_state! { self.class.transaction { save_without_transactions! } }
+ end
+
+ # Reset id and @new_record if the transaction rolls back.
+ def rollback_active_record_state!
+ id_present = has_attribute?(self.class.primary_key)
+ previous_id = id
+ previous_new_record = new_record?
+ yield
+ rescue Exception
+ @new_record = previous_new_record
+ if id_present
+ self.id = previous_id
+ else
+ @attributes.delete(self.class.primary_key)
+ @attributes_cache.delete(self.class.primary_key)
+ end
+ raise
+ end
+
+ # Executes +method+ within a transaction and captures its return value as a
+ # status flag. If the status is true the transaction is committed, otherwise
+ # a ROLLBACK is issued. In any case the status flag is returned.
+ #
+ # This method is available within the context of an ActiveRecord::Base
+ # instance.
+ def with_transaction_returning_status(method, *args)
+ status = nil
+ self.class.transaction do
+ status = send(method, *args)
+ raise ActiveRecord::Rollback unless status
+ end
+ status
+ end
+ end
+end
projects / feedcatcher.git / blobdiff