Active record pattern: Difference between revisions

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{{Short description|Concept in software engineering}}

In [[software engineering]], the '''active record pattern''' is an [[Architectural pattern (computer science)|architectural pattern]]. It is found in software that stores in-memory object data in [[relational database]]s. It was named by [[Martin Fowler (software engineer)|Martin Fowler]] in his 2003 book ''Patterns of Enterprise Application Architecture''.<ref>[https://martinfowler.com/eaaCatalog/activeRecord.html P of EAA Catalog - Active Record]</ref><ref>{{cite book |last=Fowler |first=Martin |title=Patterns of enterprise application architecture |publisher=Addison-Wesley |year=2003 |isbn=978-0-321-12742-6 |url=https://books.google.com/books?id=FyWZt5DdvFkC&lpgq=PA1&dq=Patterns%20of%20Enterprise%20Application%20Architecture%20by%20Martin%20Fowleractive+record&pg=PT187#v=onepage&q=active%20record&f=false }}</ref> The interface of an object conforming to this pattern would include functions such as Insert, Update, and Delete, plus properties that correspond more or less directly to the columns in the underlying database table.

The active record pattern is an approach to accessing data in a [[database]]. A [[database table]] or [[View (database)|view]] is wrapped into a [[class (computer science)|class]]. Thus, an [[object (computer science)|object]] instance is tied to a single row in the table. After creation of an object, a new row is added to the table upon save. Any object loaded gets its information from the database. When an object is updated, the corresponding row in the table is also updated. The wrapper class implements [[accessor]] [[Method (computer programming)|methods]] or properties for each column in the table or view.

This pattern is commonly used by object persistence tools and in [[object-relationalobject–relational mapping]] (ORM). Typically, [[foreign key]] relationships will be exposed as an object instance of the appropriate type via a property.

== Implementations ==

Implementations of the concept can be found in various [[Software framework|framework]]s for many programming environments. For example, if in a database there is a table <code>parts</code> in a database with columns <code>name</code> (string type) and <code>price</code> (number type), and the Active Record pattern is implemented in the class <code>Part</code>, the pseudo-code

{{sxhl|2=ruby|1=

part = new Part()

part.name = "Sample part"

part.price = 123.45

part.save()

}}

will create a new row in the <code>parts</code> table with the given values, and is roughly equivalent to the [[SQL]] command

<sourcesyntaxhighlight lang="sql">

INSERT INTO parts (name, price) VALUES ('Sample part', 123.45);

</syntaxhighlight>

</source>

Conversely, the class can be used to query the database:

{{sxhl|2=ruby|1=

b = Part.find_first("name", "gearbox")

}}

This will find a new <code>Part</code> object based on the first matching row from the <code>parts</code> table whose <code>name</code> column has the value "gearbox". The SQL command used might be similar to the following, depending on the SQL implementation details of the database:

<sourcesyntaxhighlight lang="sql">

SELECT * FROM parts WHERE name = 'gearbox' LIMIT 1; -- MySQL or PostgreSQL

</syntaxhighlight>

</source>

=== ColdFusion ===

[[ColdFusion]] has an open source implementation of the active record pattern.

The [[ColdFusion on Wheels]] framework has an implementation of the active record pattern. It is open source and has the added advantage of requiring no complex configuration.

=== PHP ===

PHP ActiveRecord is one [[open-source]] library designed to fulfill the active record pattern.<ref>{{cite web|title=PHP ActiveRecord|url=http://www.phpactiverecord.org/}}</ref>

Several open-source [[PHP]] frameworks also bundle their own [[Object-relational mapping|ORM]] implementing the active record pattern. Most implementations support relationships, behaviors, [[input validation|validation]], [[serialization]] and support for multiple data sources.

* [[Maghead (PHP)|Maghead]], a high performance database framework written in pure PHP, contains a class/query method generator to boost the performance. It mixes the active record pattern with repository pattern.

* [[Boiler MVC|Boiler]], an [[MVC model|MVC]] framework for PHP, contains a set of tools for auto-generation of active record models.<ref>{{cite web|title=Boiler Documentation: Models|url=http://www.bluelightstudios.co.uk/tutorial-4-models/}}</ref> The project, designed for data-centered projects, aims to automate as much of the development process as possible,<ref>{{cite web|title=YouTube demonstration of automation tools|url=https://www.youtube.com/watch?v=M7PG2rTYDGA}}</ref> using [[Apache Ant]]. Although a new addition to Open Source market,<ref>{{cite web|title=Open Source Code, hosted on Github|url=https://github.com/ivebeenlinuxed/Boiler}}</ref> the project is already in use in many live applications, both commercially and open. The framework currently only supports [[MySQL]] though the developers have reported some commercial work in Postgres.

* [[Cygnite PHP Framework]]'s default database layer implements Active Record pattern which closely resemble with [[Ruby on Rails]].<ref>{{cite web|title=Cygnite Framework Documentation: Active Record|url=http://www.cygniteframework.com/2014/06/active-record.html}}</ref>

* [[Eloquent ORM]] its included with Laravel. Eloquent implements the active record pattern, closely resembling that of [[Ruby on Rails]] <ref>{{cite web|title=Laravel Documentation: Eloquent ORM|url=https://laravel.com/docs/5.6/eloquent}}</ref>

* [[CakePHP]]'s ORM implements the active record pattern,<ref>{{cite web|title=CakePHP (most popular PHP framework)|url=http://stanford.wikia.com/wiki/CakePHP_(most_popular_PHP_framework)|work=Stanford University Wiki}}</ref> but as of version 2.x queries return arrays of data, with levels of '''related data''' as required. Version 3.0 uses objects and offers a hybrid implementation of ActiveRecord and Datamapper patterns.

* [[Lithium (software)|Lithium]]'s ORM implements active record.

* [[Symfony]]'s default database layer and ORM "[[Doctrine (PHP)|Doctrine]]" does not implement active record but rather a [[Data mapper pattern|data mapper]] approach.

* <span id="codeigniter">[[EllisLab#CodeIgniter|CodeIgniter]]</span> has a query builder it calls "ActiveRecord", but which does not implement the Active Record pattern. Instead, it implements what the user guide refers to as a modified version of the pattern. The Active Record functionality in CodeIgniter can be achieved by using either CodeIgniter DataMapper library or CodeIgniter Gas ORM library.

* [[Yii]]'s ORM also implements the active record pattern.<ref>{{cite web|title=The Definitive Guide to Yii: Active Record|url=http://www.yiiframework.com/doc/guide/1.1/en/database.ar}}</ref>

* [[Propel (PHP)|Propel]] also implements the active record pattern.<ref>{{cite web|title=Propel: Active Record Reference|url=http://propelorm.org/documentation/reference/active-record.html}}</ref>

* Paris is A lightweight Active Record implementation for PHP5, built on top of Idiorm.<ref>{{cite web|title=Github: j4mie/paris|url=https://github.com/j4mie/paris}}</ref>

=== Ruby ===

The [[Ruby (programming language)|Ruby]] library ActiveRecord implements ORM. It creates a [[Persistence (computer science)|persistable]] ___domain model from business objects and database tables, where logic and data are presented as a unified package. It largely simplifies object-record mapping by assuming homogeneous identification method (i.e. [[Surrogate key]]) by virtue of [[convention over configuration]]. ActiveRecord adds [[Inheritance (computer science)|inheritance]] and [[Association (object-oriented programming)|associations]] to the pattern above, solving two substantial limitations of that pattern. A set of macros acts as a ___domain language for the latter, and the [[Single Table Inheritance]] pattern is integrated for the former; thus, ActiveRecord increases the functionality of the active record pattern approach to database interaction. ActiveRecord is the default ‘model’ component of the [[model-view-controller]] web-application framework [[Ruby on Rails]], and is also a stand-alone ORM package for other Ruby applications. In both forms, it was conceived of by [[David Heinemeier Hansson]], and has been improved upon by a number of contributors.<ref>{{cite web|url=https://github.com/rails/rails/tree/master/activerecord|title=Ruby Active Record|accessdate=2013-04-12}}</ref>

Other ORMs have been released since ActiveRecord first appeared. For example, [[DataMapper (Ruby)|DataMapper]] and [[Sequel (Ruby)|Sequel]]. These ORMs include improvements over the original ActiveRecord framework.{{POV statement|date=May 2012}} As a response to their release and adoption by the Rails community, Ruby on Rails v3.0 became independent of an ORM system, so that Rails users can instead use DataMapper or Sequel as their ORM.

=== Python ===

[[Django_(web_framework)|Django]], one of [[Python_(programming_language)|Python]]'s many web frameworks, uses the Active Record pattern for its ORM.<ref>{{cite web|url=https://docs.djangoproject.com/en/1.11/misc/design-philosophies/#models|accessdate=2017-06-28}}</ref>

=== Java ===

The [[Java (programming language)|Java language]] implements the Active Record pattern via the [[ActiveJDBC]] library. ActiveJDBC is an implementation of Active Record design pattern inspired by [[Ruby on Rails]] ActiveRecord. ActiveJDBC is lightweight, fast, small and does not require any configuration.

[[ActiveJPA]] and [[Java Object Oriented Querying|jOOQ (for Java Object Oriented Querying)]] implements the Active record pattern, combining active records with [[Automatic programming|source code generation]] and a querying DSL similar to [[SQL]] allowing for retrieving active records using complex SQL statements.

The [[Play framework]] is a Java web framework which implements the Active Record pattern, using ideas from [[Ruby on Rails]].

[https://github.com/doe300/jactiverecord JActiveRecord] is yet another library providing easy [[Object-relational mapping|ORM]] mapping for Java, inspired by [[Ruby on Rails]] ActiveRecord but more focused on Java's type-safety.

=== Dart ===

The [[Dart (programming language)|Dart]] language implements the Active Record pattern via the [https://github.com/HannesRammer/Dartabase/tree/master/dartabase_migration Dartabase Migration] and [https://github.com/HannesRammer/Dartabase/tree/master/dartabase_model Dartabase Model] packages

[https://github.com/HannesRammer/Dartabase/tree/master/dartabase_migration Dartabase Migration]

Serverside Database Object Models for simple data manipulation currently supporting MySQL/PGSQL inspired by Ruby on Rails Migration

[https://github.com/HannesRammer/Dartabase/tree/master/dartabase_model Dartabase Model]

Serverside Database migration for simple version controlled database structure manipulation currently supporting MySQL/PGSQL inspired by Ruby on Rails Model

now console and GUI (build in Polymer 1.0)

=== Other languages ===

There are several open source implementations of the Active Record pattern in other languages, including [[JavaScript]] (e.g., [[ActiveJS]]'s Active Record<ref name="ActiveJS">{{cite web|url=http://www.activejs.org/activerecord/ActiveRecord/index.html|title=ActiveJS Active Record|accessdate=2011-07-28}}</ref>), [[Perl]] ([[DBIx::Class]]), [[ActionScript]], [[Haxe]] (SPOD<ref name="HaxeSPOD">{{cite web|url=http://haxe.org/manual/spod|title=SPOD Macros|accessdate=2013-01-09}}</ref>), [[C Sharp (programming language)|C#]],<ref name="CastleActiveRecord">{{cite web|title=Castle ActiveRecord|url=http://www.castleproject.org/projects/activerecord/|accessdate=14 January 2014}}</ref> [[Objective-C]]<ref>{{cite web|title=Objective Record|url=https://github.com/mneorr/Objective-Record|accessdate=14 January 2013}}</ref> and [[Scala (programming language)|Scala]].<ref>{{cite web|title=Scala Active Record|url=https://github.com/aselab/scala-activerecord|accessdate=4 December 2013}}</ref>

== Criticism ==

=== TestabilityLarge files ===

Because the data and the database access methods are in the same file, those files end up being bigger.

Due to the coupling of database interaction and application logic when using the active record pattern, unit testing an active record object without a database becomes difficult.{{citation needed |date=May 2015}} The negative effects on testability in the active record pattern can be minimized by using [[mock object|mocking]] or [[dependency injection]] frameworks to substitute the real data tier with a simulated one.{{citation needed |date=May 2015}}

=== Single responsibility principle and separation of concerns ===

Another critique of the active record pattern is that, also due to the strong coupling of database interaction and application logic, an active record object does not follow the [[single responsibility principle]] and [[separation of concerns]]. This is opposed to [[multitier architecture]], which properly addresses these practices.{{citation needed |date=November 2019}}{{Clarify|date=August 2018}} Because of this, the active record pattern is best and most often employed in simple applications that are all forms-over-data with [[Create, read, update and delete|CRUD]] functionality, or only as one part of an architecture.{{citation needed |date=November 2019}} Typically that part is data access and why several ORMs implement the active record pattern.

[[single responsibility principle]] and [[separation of concerns]] as opposed to [[multitier architecture]] which properly addresses these practices. Because of this, the active record pattern is best and most often employed in simple applications that are all forms-over-data with [[Create, read, update and delete|CRUD]] functionality, or only as one part of an architecture. Typically that part is data access and why several ORMs implement the active record pattern.

=== Distributed systems ===

Record based patterns work poorly in distributed systems especially where concurrency is impossible ( eg offline ). i.e. 2 updates both may have 1 field that is correct but only one of the 2 records can win.{{Clarify}}

== See also ==

* [[Business object]]

* [[Create, read, update and delete|CRUD]]

* [[Data mapper pattern]]

* [[Object-relational mapping]]

* [[{{Annotated link |Business object]]}}

== References ==

* [[{{Annotated link |Create, read, update and delete|CRUD]]}}

{{Reflist|colwidth=35em}}

* [[{{Annotated link |Data mapper pattern]]}}

* {{Annotated link |Object–relational mapping}}

== External linksReferences ==

{{Reflist|colwidth=35em}}

* [https://github.com/rails/rails/tree/master/activerecord Ruby implementation]

* [https://metacpan.org/module/DBIx::Class DBIx::Class Perl Implementation]

* [http://www.phpactiverecord.org/ PHP implementation]

* [http://www.castleproject.org/projects/activerecord/ .NET implementation]

* [https://code.google.com/p/air-activerecord/ AIR Active Record project home]

* [https://github.com/scandio/troba/blob/master/doc/active-record-extension.md troba Active record extension]

{{Design Patterns Patterns}}

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[[Category:Architectural pattern (computer science)]]

[[Category:Software design patterns]]