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360 lines
15 KiB
Ruby
360 lines
15 KiB
Ruby
require 'thread'
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module ActiveRecord
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# See ActiveRecord::Transactions::ClassMethods for documentation.
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module Transactions
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extend ActiveSupport::Concern
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class TransactionError < ActiveRecordError # :nodoc:
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end
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included do
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define_callbacks :commit, :rollback, :terminator => "result == false", :scope => [:kind, :name]
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end
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# = Active Record Transactions
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#
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# Transactions are protective blocks where SQL statements are only permanent
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# if they can all succeed as one atomic action. The classic example is a
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# transfer between two accounts where you can only have a deposit if the
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# withdrawal succeeded and vice versa. Transactions enforce the integrity of
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# the database and guard the data against program errors or database
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# break-downs. So basically you should use transaction blocks whenever you
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# have a number of statements that must be executed together or not at all.
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#
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# For example:
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#
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# ActiveRecord::Base.transaction do
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# david.withdrawal(100)
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# mary.deposit(100)
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# end
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#
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# This example will only take money from David and give it to Mary if neither
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# +withdrawal+ nor +deposit+ raise an exception. Exceptions will force a
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# ROLLBACK that returns the database to the state before the transaction
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# began. Be aware, though, that the objects will _not_ have their instance
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# data returned to their pre-transactional state.
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#
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# == Different Active Record classes in a single transaction
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#
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# Though the transaction class method is called on some Active Record class,
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# the objects within the transaction block need not all be instances of
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# that class. This is because transactions are per-database connection, not
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# per-model.
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#
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# In this example a +balance+ record is transactionally saved even
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# though +transaction+ is called on the +Account+ class:
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#
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# Account.transaction do
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# balance.save!
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# account.save!
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# end
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#
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# The +transaction+ method is also available as a model instance method.
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# For example, you can also do this:
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#
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# balance.transaction do
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# balance.save!
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# account.save!
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# end
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#
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# == Transactions are not distributed across database connections
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#
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# A transaction acts on a single database connection. If you have
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# multiple class-specific databases, the transaction will not protect
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# interaction among them. One workaround is to begin a transaction
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# on each class whose models you alter:
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#
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# Student.transaction do
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# Course.transaction do
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# course.enroll(student)
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# student.units += course.units
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# end
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# end
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#
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# This is a poor solution, but fully distributed transactions are beyond
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# the scope of Active Record.
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#
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# == +save+ and +destroy+ are automatically wrapped in a transaction
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#
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# Both +save+ and +destroy+ come wrapped in a transaction that ensures
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# that whatever you do in validations or callbacks will happen under its
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# protected cover. So you can use validations to check for values that
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# the transaction depends on or you can raise exceptions in the callbacks
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# to rollback, including <tt>after_*</tt> callbacks.
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#
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# As a consequence changes to the database are not seen outside your connection
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# until the operation is complete. For example, if you try to update the index
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# of a search engine in +after_save+ the indexer won't see the updated record.
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# The +after_commit+ callback is the only one that is triggered once the update
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# is committed. See below.
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#
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# == Exception handling and rolling back
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#
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# Also have in mind that exceptions thrown within a transaction block will
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# be propagated (after triggering the ROLLBACK), so you should be ready to
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# catch those in your application code.
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#
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# One exception is the <tt>ActiveRecord::Rollback</tt> exception, which will trigger
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# a ROLLBACK when raised, but not be re-raised by the transaction block.
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#
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# *Warning*: one should not catch <tt>ActiveRecord::StatementInvalid</tt> exceptions
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# inside a transaction block. <tt>ActiveRecord::StatementInvalid</tt> exceptions indicate that an
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# error occurred at the database level, for example when a unique constraint
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# is violated. On some database systems, such as PostgreSQL, database errors
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# inside a transaction cause the entire transaction to become unusable
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# until it's restarted from the beginning. Here is an example which
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# demonstrates the problem:
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#
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# # Suppose that we have a Number model with a unique column called 'i'.
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# Number.transaction do
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# Number.create(:i => 0)
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# begin
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# # This will raise a unique constraint error...
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# Number.create(:i => 0)
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# rescue ActiveRecord::StatementInvalid
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# # ...which we ignore.
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# end
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#
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# # On PostgreSQL, the transaction is now unusable. The following
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# # statement will cause a PostgreSQL error, even though the unique
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# # constraint is no longer violated:
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# Number.create(:i => 1)
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# # => "PGError: ERROR: current transaction is aborted, commands
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# # ignored until end of transaction block"
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# end
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#
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# One should restart the entire transaction if an
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# <tt>ActiveRecord::StatementInvalid</tt> occurred.
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#
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# == Nested transactions
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#
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# +transaction+ calls can be nested. By default, this makes all database
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# statements in the nested transaction block become part of the parent
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# transaction. For example, the following behavior may be surprising:
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#
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# User.transaction do
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# User.create(:username => 'Kotori')
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# User.transaction do
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# User.create(:username => 'Nemu')
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# raise ActiveRecord::Rollback
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# end
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# end
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#
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# creates both "Kotori" and "Nemu". Reason is the <tt>ActiveRecord::Rollback</tt>
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# exception in the nested block does not issue a ROLLBACK. Since these exceptions
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# are captured in transaction blocks, the parent block does not see it and the
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# real transaction is committed.
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#
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# In order to get a ROLLBACK for the nested transaction you may ask for a real
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# sub-transaction by passing <tt>:requires_new => true</tt>. If anything goes wrong,
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# the database rolls back to the beginning of the sub-transaction without rolling
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# back the parent transaction. If we add it to the previous example:
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#
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# User.transaction do
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# User.create(:username => 'Kotori')
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# User.transaction(:requires_new => true) do
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# User.create(:username => 'Nemu')
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# raise ActiveRecord::Rollback
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# end
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# end
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#
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# only "Kotori" is created. (This works on MySQL and PostgreSQL, but not on SQLite3.)
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#
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# Most databases don't support true nested transactions. At the time of
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# writing, the only database that we're aware of that supports true nested
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# transactions, is MS-SQL. Because of this, Active Record emulates nested
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# transactions by using savepoints on MySQL and PostgreSQL. See
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# http://dev.mysql.com/doc/refman/5.0/en/savepoint.html
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# for more information about savepoints.
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#
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# === Callbacks
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#
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# There are two types of callbacks associated with committing and rolling back transactions:
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# +after_commit+ and +after_rollback+.
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#
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# +after_commit+ callbacks are called on every record saved or destroyed within a
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# transaction immediately after the transaction is committed. +after_rollback+ callbacks
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# are called on every record saved or destroyed within a transaction immediately after the
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# transaction or savepoint is rolled back.
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#
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# These callbacks are useful for interacting with other systems since you will be guaranteed
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# that the callback is only executed when the database is in a permanent state. For example,
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# +after_commit+ is a good spot to put in a hook to clearing a cache since clearing it from
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# within a transaction could trigger the cache to be regenerated before the database is updated.
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#
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# === Caveats
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#
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# If you're on MySQL, then do not use DDL operations in nested transactions
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# blocks that are emulated with savepoints. That is, do not execute statements
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# like 'CREATE TABLE' inside such blocks. This is because MySQL automatically
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# releases all savepoints upon executing a DDL operation. When +transaction+
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# is finished and tries to release the savepoint it created earlier, a
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# database error will occur because the savepoint has already been
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# automatically released. The following example demonstrates the problem:
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#
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# Model.connection.transaction do # BEGIN
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# Model.connection.transaction(:requires_new => true) do # CREATE SAVEPOINT active_record_1
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# Model.connection.create_table(...) # active_record_1 now automatically released
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# end # RELEASE savepoint active_record_1
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# # ^^^^ BOOM! database error!
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# end
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#
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# Note that "TRUNCATE" is also a MySQL DDL statement!
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module ClassMethods
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# See ActiveRecord::Transactions::ClassMethods for detailed documentation.
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def transaction(options = {}, &block)
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# See the ConnectionAdapters::DatabaseStatements#transaction API docs.
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connection.transaction(options, &block)
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end
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def after_commit(*args, &block)
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options = args.last
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if options.is_a?(Hash) && options[:on]
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options[:if] = Array.wrap(options[:if])
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options[:if] << "transaction_include_action?(:#{options[:on]})"
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end
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set_callback(:commit, :after, *args, &block)
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end
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def after_rollback(*args, &block)
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options = args.last
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if options.is_a?(Hash) && options[:on]
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options[:if] = Array.wrap(options[:if])
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options[:if] << "transaction_include_action?(:#{options[:on]})"
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end
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set_callback(:rollback, :after, *args, &block)
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end
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end
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# See ActiveRecord::Transactions::ClassMethods for detailed documentation.
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def transaction(options = {}, &block)
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self.class.transaction(options, &block)
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end
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def destroy #:nodoc:
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with_transaction_returning_status { super }
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end
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def save(*) #:nodoc:
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rollback_active_record_state! do
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with_transaction_returning_status { super }
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end
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end
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def save!(*) #:nodoc:
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with_transaction_returning_status { super }
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end
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# Reset id and @new_record if the transaction rolls back.
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def rollback_active_record_state!
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remember_transaction_record_state
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yield
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rescue Exception
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IdentityMap.remove(self) if IdentityMap.enabled?
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restore_transaction_record_state
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raise
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ensure
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clear_transaction_record_state
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end
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# Call the after_commit callbacks
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def committed! #:nodoc:
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run_callbacks :commit
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ensure
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clear_transaction_record_state
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end
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# Call the after rollback callbacks. The restore_state argument indicates if the record
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# state should be rolled back to the beginning or just to the last savepoint.
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def rolledback!(force_restore_state = false) #:nodoc:
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run_callbacks :rollback
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ensure
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IdentityMap.remove(self) if IdentityMap.enabled?
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restore_transaction_record_state(force_restore_state)
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end
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# Add the record to the current transaction so that the :after_rollback and :after_commit callbacks
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# can be called.
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def add_to_transaction
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if self.class.connection.add_transaction_record(self)
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remember_transaction_record_state
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end
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end
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# Executes +method+ within a transaction and captures its return value as a
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# status flag. If the status is true the transaction is committed, otherwise
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# a ROLLBACK is issued. In any case the status flag is returned.
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#
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# This method is available within the context of an ActiveRecord::Base
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# instance.
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def with_transaction_returning_status
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status = nil
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self.class.transaction do
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add_to_transaction
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status = yield
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raise ActiveRecord::Rollback unless status
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end
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status
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end
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protected
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# Save the new record state and id of a record so it can be restored later if a transaction fails.
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def remember_transaction_record_state #:nodoc
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@_start_transaction_state ||= {}
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@_start_transaction_state[:id] = id if has_attribute?(self.class.primary_key)
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unless @_start_transaction_state.include?(:new_record)
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@_start_transaction_state[:new_record] = @new_record
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end
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unless @_start_transaction_state.include?(:destroyed)
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@_start_transaction_state[:destroyed] = @destroyed
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end
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@_start_transaction_state[:level] = (@_start_transaction_state[:level] || 0) + 1
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end
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# Clear the new record state and id of a record.
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def clear_transaction_record_state #:nodoc
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if defined?(@_start_transaction_state)
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@_start_transaction_state[:level] = (@_start_transaction_state[:level] || 0) - 1
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remove_instance_variable(:@_start_transaction_state) if @_start_transaction_state[:level] < 1
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end
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end
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# Restore the new record state and id of a record that was previously saved by a call to save_record_state.
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def restore_transaction_record_state(force = false) #:nodoc
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if defined?(@_start_transaction_state)
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@_start_transaction_state[:level] = (@_start_transaction_state[:level] || 0) - 1
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if @_start_transaction_state[:level] < 1
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restore_state = remove_instance_variable(:@_start_transaction_state)
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@attributes = @attributes.dup if @attributes.frozen?
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@new_record = restore_state[:new_record]
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@destroyed = restore_state[:destroyed]
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if restore_state.has_key?(:id)
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self.id = restore_state[:id]
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else
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@attributes.delete(self.class.primary_key)
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@attributes_cache.delete(self.class.primary_key)
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end
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end
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end
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end
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# Determine if a record was created or destroyed in a transaction. State should be one of :new_record or :destroyed.
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def transaction_record_state(state) #:nodoc
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@_start_transaction_state[state] if defined?(@_start_transaction_state)
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end
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# Determine if a transaction included an action for :create, :update, or :destroy. Used in filtering callbacks.
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def transaction_include_action?(action) #:nodoc
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case action
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when :create
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transaction_record_state(:new_record)
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when :destroy
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destroyed?
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when :update
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!(transaction_record_state(:new_record) || destroyed?)
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end
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end
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end
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end
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