Skip to main content

Active Records

  • Active Record is the M in the MVC model
  • It is an implementation of the Active Record pattern which itself is a description of an Object Relational Mapping system (ORM)
  • Active Record gives us several mechanism
    • Represent models and their data
    • Represent associations between these models
    • Represent inheritance hierarchies through related models
    • Validate models before they get persisted to the database
    • Perform database operation in an object-oriented fashion

Naming Conventions​

  • Active Record uses some naming conventions to find out how the mapping between models and database tables should be created.
  • Rails will pluralize the class names to find the respective database table
  • When using class names composed of tow or more word, the model class name should follow the Ruby conventions, using CamelCase form
    • Model class: Singular with the first letter of each word capitalized (e.g BookClub)
    • Database table: Plural with underscores separating words (e.g book_clubs)

Creating Active Record Models​

  • To create Active Record models, subclass the ApplicationRecord class

Create​

  • Active Record objects can be created from a hash, a block, or have their attributes manually set after creation.
    - The `new` method will return a new object and has to call `save` to save to database
    - The `create` method will return the object and save it to database

Validation​

  • Active Record allows you to validate the state of a model before it gets written into the database
  • The methods save and update take into account when running
    - return `false` when the validation fails and they don't actually perform any operations on the database
    - have a bang counterpart (`save!` and `update`) which are stricter in that they raise the exception `ActiveRecord::RecordInvalid` if validation fails

Active Models

  • A library containing various modules used in developing classes that need some features present on Active Record

  • Some features already included in ActiveRecord::Base so we can immediately use like this

  • There are cases where classes in Rails require model-like features, but they are not tied to any table in a database => include in your class

  • E.g: we have a Person class with name and id attributes. We want to add validations to these attributes.

  • Ref: https://api.rubyonrails.org/classes/ActiveModel.html