Active record pattern

<h2 id="implementations">Implementations</h2>
<p>Implementations of the concept can be found in various <a href="/facts/Software_framework/EWasA8sG">frameworks</a> for many programming environments. For example, if there is a table parts in a database with columns name (string type) and price (number type), and the Active Record pattern is implemented in the class Part, the pseudo-code
</p>
part = new Part()
part.name = "Sample part"
part.price = 123.45
part.save()

<p>will create a new row in the parts table with the given values, and is roughly equivalent to the <a href="/facts/SQL/UjQLJcYm">SQL</a> command
</p>
INSERT INTO parts (name, price) VALUES ('Sample part', 123.45);

<p>Conversely, the class can be used to query the database:
</p>
b = Part.find_first("name", "gearbox")

<p>This will find a new Part object based on the first matching row from the parts table whose name column has the value "gearbox". The SQL command used might be similar to the following, depending on the SQL implementation details of the database:
</p>
SELECT * FROM parts WHERE name = 'gearbox' LIMIT 1; -- MySQL or PostgreSQL

<h2 id="criticism">Criticism</h2>
<h3>Large files</h3>
<p>Because the data and the database access methods are in the same file, those files end up being bigger.
</p>
<h3>Single responsibility principle and separation of concerns</h3>
<p>Another critique of the active record pattern is that, due to the strong coupling of database interaction and application logic, an active record object does not follow the <a href="/facts/Single_responsibility_principle/6agMc10w">single responsibility principle</a> and <a href="/facts/Separation_of_concerns/Tx8jawNT">separation of concerns</a>. This is opposed to <a href="/facts/Multitier_architecture/cUTM2sU9">multitier architecture</a>, 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 <a href="/facts/Create%2c_read%2c_update_and_delete/8KwxY2eH">CRUD</a> functionality, or only as one part of an architecture. Typically that part is data access and why several ORMs implement the active record pattern.
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Business_object/qRaCFz1u">Business object</a> – Entity within a multi-tiered software application</li>
<li><a href="/facts/Create%2c_read%2c_update_and_delete/8KwxY2eH">CRUD</a> – Basic operations of a computer database</li>
<li><a href="/facts/Data_mapper_pattern/7QqgHz59">Data mapper pattern</a> – Architectural pattern in software engineering</li>
<li><a href="/facts/Object%25E2%2580%2593relational_mapping/sjIPEIfq">Object–relational mapping</a> – Programming technique</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>P of EAA Catalog - Active Record <a href="https://martinfowler.com/eaaCatalog/activeRecord.html" target="_blank">https://martinfowler.com/eaaCatalog/activeRecord.html</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Fowler, Martin (2003). Patterns of enterprise application architecture. Addison-Wesley. ISBN 978-0-321-12742-6. <a href="978-0-321-12742-6" target="_blank">978-0-321-12742-6</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
</ol>

Active record pattern open-in-new

Active record pattern