Lably
Skip to content

Active record pattern

Concept in software engineering

  • 12 min read
  • 3 chapters

Related on Lably

Through Relational database, Class (programming) and Object (computer science)

LabRelational DatabasesLabAI & Python Builds (Medha AI)Lab · Class 8–11Image Classifier

The Active Record pattern is a Data Access Layer that performs bidirectional transfer of data between a persistent data store (often a relational database) and an in-memory data representation (the domain layer). A database table or view is wrapped into a class. Thus, an 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 methods or properties for each column in the table or view.

This pattern is commonly used by object persistence tools and in object–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 frameworks 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

<span id="mwKA"></span><span class="n" id="mwKQ">Part</span><span class="w" id="mwKg"> </span><span class="n" id="mwKw">part</span><span class="w" id="mwLA"> </span><span class="o" id="mwLQ">=</span><span class="w" id="mwLg"> </span><span class="k" id="mwLw">new</span><span class="w" id="mwMA"> </span><span class="n" id="mwMQ">Part</span><span class="p" id="mwMg">(</span><span class="s" id="mwMw">"Sample part"</span><span class="p" id="mwNA">,</span><span class="w" id="mwNQ"> </span><span class="mf" id="mwNg">123.45</span><span class="p" id="mwNw">);</span>

will create a new row in the parts table with the given values, and is roughly equivalent to the SQL command

<span id="mwPQ"></span><span class="k" id="mwPg">INSERT</span><span class="w" id="mwPw"> </span><span class="k" id="mwQA">INTO</span><span class="w" id="mwQQ"> </span><span class="n" id="mwQg">parts</span><span class="w" id="mwQw"> </span><span class="p" id="mwRA">(</span><span class="n" id="mwRQ">name</span><span class="p" id="mwRg">,</span><span class="w" id="mwRw"> </span><span class="n" id="mwSA">price</span><span class="p" id="mwSQ">)</span><span class="w" id="mwSg"> </span><span class="k" id="mwSw">VALUES</span><span class="w" id="mwTA"> </span><span class="p" id="mwTQ">(</span><span class="s1" id="mwTg">'Sample part'</span><span class="p" id="mwTw">,</span><span class="w" id="mwUA"> </span><span class="mi" id="mwUQ">123</span><span class="p" id="mwUg">.</span><span class="mi" id="mwUw">45</span><span class="p" id="mwVA">);</span>

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

<span id="mwWA"></span><span class="n" id="mwWQ">Part</span><span class="w" id="mwWg"> </span><span class="n" id="mwWw">b</span><span class="w" id="mwXA"> </span><span class="o" id="mwXQ">=</span><span class="w" id="mwXg"> </span><span class="n" id="mwXw">parts</span><span class="p" id="mwYA">.</span><span class="na" id="mwYQ">stream</span><span class="p" id="mwYg">()</span> <span class="w" id="mwYw"> </span><span class="p" id="mwZA">.</span><span class="na" id="mwZQ">filter</span><span class="p" id="mwZg">(</span><span class="n" id="mwZw">p</span><span class="w" id="mwaA"> </span><span class="o" id="mwaQ">-></span><span class="w" id="mwag"> </span><span class="s" id="mwaw">"gearbox"</span><span class="p" id="mwbA">.</span><span class="na" id="mwbQ">equals</span><span class="p" id="mwbg">(</span><span class="n" id="mwbw">p</span><span class="p" id="mwcA">.</span><span class="na" id="mwcQ">getName</span><span class="p" id="mwcg">()))</span> <span class="w" id="mwcw"> </span><span class="p" id="mwdA">.</span><span class="na" id="mwdQ">findFirst</span><span class="p" id="mwdg">()</span> <span class="w" id="mwdw"> </span><span class="p" id="mweA">.</span><span class="na" id="mweQ">orElse</span><span class="p" id="mweg">(</span><span class="kc" id="mwew">null</span><span class="p" id="mwfA">);</span>

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:

<span id="mwgw"></span><span class="k" id="mwhA">SELECT</span><span class="w" id="mwhQ"> </span><span class="o" id="mwhg">*</span><span class="w" id="mwhw"> </span><span class="k" id="mwiA">FROM</span><span class="w" id="mwiQ"> </span><span class="n" id="mwig">parts</span><span class="w" id="mwiw"> </span><span class="k" id="mwjA">WHERE</span><span class="w" id="mwjQ"> </span><span class="n" id="mwjg">name</span><span class="w" id="mwjw"> </span><span class="o" id="mwkA">=</span><span class="w" id="mwkQ"> </span><span class="s1" id="mwkg">'gearbox'</span><span class="w" id="mwkw"> </span><span class="k" id="mwlA">LIMIT</span><span class="w" id="mwlQ"> </span><span class="mi" id="mwlg">1</span><span class="p" id="mwlw">;</span><span class="w" id="mwmA"> </span><span class="c1" id="mwmQ">-- MySQL or PostgreSQL</span>

Various libraries implement an active record pattern framework, such as POCO C++ Libraries in library Poco::ActiveRecord.

Sign in to keep reading

2 more chapters are free with a Lably account.

More in Computing and communication

ISBNUnique numeric book identifier since 1970X (social network)American social networking serviceWayback MachineDigital archive by the Internet ArchivePython (programming language)General-purpose programming languageMacOSOperating system for Apple computersUnicodeCharacter encoding standard