Rails Model Reference

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See Rails Model and Data for our guide through this topic.

Terminal Commands

  • rails new store - Create a new Rails app from scratch in a new store folder.

The following commands are entered in the terminal in your app's directory:

  • bundle install - Install the gems (bundled Ruby libraries) for your Rails App.
  • rails generate model Product name:string - Create Product model with a column name (which will store strings of text).
  • rails g migration AddPriceToProducts price:integer - generates the migration file to add an integer price column to the product table.
  • rake db:migrate - Run migration files to apply changes to your database.
  • rake test - Run your application's tests.

Rails Console

You can connect with your app/database and perform standard CRUD operations in the Rails console. This is useful for trying code out.

  • rails console (or rails c) - Enter this command in your terminal to start the Rails console.
  • reload! - Enter this in your running Rails console to reload changes

(See Active Record Migrations and the Rails Command Line for more.)


These are the 4 basic "CRUD" operations:

  • Create - Product .create(name: "Phonograph" , description: "Records sound" ) - Creates and saves a new record to the database. Use .new to instantiate an object without saving it until .save is called.
  • Read - There are many methods for reading data, such as:
    • products = Product .all - return collection of all products
    • products = Product .where(name: "Hammer" , price: 10) - returns all products with both these attributes
    • product = Product .find_by(name: "Cow" ) - returns first product named "Cow"
  • Update - After retrieving a record, you can modify and save it:
    product.description = "It moos"
  • Delete - Don't like your Cow? You can remove it from the database: product.destroy

See Active Record Basics and Active Record Query Interface for more.

Model Relationships

Add a column_id to products to associate each product with a category:

Select products from category

Associate products with a category in Rails:

class Product < ActiveRecord::Base
 belongs_to :category

Associate categories with many products:

class Category < ActiveRecord::Base
  has_many :products

You can now use this code:

cat1 = Category.first
cat1.products #returns products in `cat1`
prod1 = Product.first
prod1.categories # returns category of `prod1`

See Active Record Associations for more.


Validations are added to a model to ensure only valid data is saved to the database. Here's the format for a simple validation:

validates :column, property: value

For example:

 validates :name, presence: true

This will ensure that records have a name before they are saved to the database.

See Rails Validations for more.

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