File: README — Documentation for transaction-simple (1.2.0)

Transaction::Simple for Ruby

Simple object transaction support for Ruby

Introduction

Transaction::Simple provides a generic way to add active transactional support to objects. The transaction methods added by this module will work with most objects, excluding those that cannot be Marshal-ed (bindings, procedure objects, IO instances, or singleton objects).

The transactions supported by Transaction::Simple are not backend transaction; that is, they have nothing to do with any sort of data store. They are "live" transactions occurring in memory and in the object itself. This is to allow "test" changes to be made to an object before making the changes permanent.

Transaction::Simple can handle an "infinite" number of transactional levels (limited only by memory). If I open two transactions, commit the first, but abort the second, the object will revert to the original version.

Transaction::Simple supports "named" transactions, so that multiple levels of transactions can be committed, aborted, or rewound by referring to the appropriate name of the transaction. Names may be any object except nil.

Thanks to David Black and Mauricio Fern?ndez for their help with this library.

Usage

include 'transaction/simple'

v = "Hello, you."               # => "Hello, you."
v.extend(Transaction::Simple)   # => "Hello, you."

v.start_transaction             # => ... (a Marshal string)
v.transaction_open?             # => true
v.gsub!(/you/, "world")         # => "Hello, world."

v.rewind_transaction            # => "Hello, you."
v.transaction_open?             # => true

v.gsub!(/you/, "HAL")           # => "Hello, HAL."
v.abort_transaction             # => "Hello, you."
v.transaction_open?             # => false

v.start_transaction             # => ... (a Marshal string)
v.start_transaction             # => ... (a Marshal string)

v.transaction_open?             # => true
v.gsub!(/you/, "HAL")           # => "Hello, HAL."

v.commit_transaction            # => "Hello, HAL."
v.transaction_open?             # => true
v.abort_transaction             # => "Hello, you."
v.transaction_open?             # => false

Named Transaction Usage

v = "Hello, you."               # => "Hello, you."
v.extend(Transaction::Simple)   # => "Hello, you."

v.start_transaction(:first)     # => ... (a Marshal string)
v.transaction_open?             # => true
v.transaction_open?(:first)     # => true
v.transaction_open?(:second)    # => false
v.gsub!(/you/, "world")         # => "Hello, world."

v.start_transaction(:second)    # => ... (a Marshal string)
v.gsub!(/world/, "HAL")         # => "Hello, HAL."
v.rewind_transaction(:first)    # => "Hello, you."
v.transaction_open?             # => true
v.transaction_open?(:first)     # => true
v.transaction_open?(:second)    # => false

v.gsub!(/you/, "world")         # => "Hello, world."
v.start_transaction(:second)    # => ... (a Marshal string)
v.gsub!(/world/, "HAL")         # => "Hello, HAL."
v.transaction_name              # => :second
v.abort_transaction(:first)     # => "Hello, you."
v.transaction_open?             # => false

v.start_transaction(:first)     # => ... (a Marshal string)
v.gsub!(/you/, "world")         # => "Hello, world."
v.start_transaction(:second)    # => ... (a Marshal string)
v.gsub!(/world/, "HAL")         # => "Hello, HAL."

v.commit_transaction(:first)    # => "Hello, HAL."
v.transaction_open?             # => false

Contraindications

While Transaction::Simple is very useful, it has some severe limitations that must be understood. Transaction::Simple:

uses Marshal. Thus, any object which cannot be Marshal-ed cannot use Transaction::Simple.
does not manage resources. Resources external to the object and its instance variables are not managed at all. However, all instance variables and objects "belonging" to those instance variables are managed. If there are object reference counts to be handled, Transaction::Simple will probably cause problems.
is not thread-safe. In the ACID ("atomic, consistent, isolated, durable") test, Transaction::Simple provides C and D, but it is up to the user of Transaction::Simple to provide isolation. Transactions should be considered "critical sections" in multi-threaded applications. Thread safety can be ensured with Transaction::Simple::ThreadSafe.
does not maintain Object#__id__ values on rewind or abort. This may change for future versions that will be Ruby 1.8 or better only.