Rails Model Reference
See Rails Model and Data for our guide through this topic.
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.
You can connect with your app/database and perform standard CRUD operations in the Rails console. This is useful for trying code out.
rails c) - Enter this command in your terminal to start the Rails console.
reload!- Enter this in your running Rails console to reload changes
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
.newto instantiate an object without saving it until
- 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:
Add a column_id to products to associate each product with a category:
Associate products with a category in Rails:
class Product < ActiveRecord::Base belongs_to :category end
Associate categories with many products:
class Category < ActiveRecord::Base has_many :products end
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
validates :name, presence: true
This will ensure that records have a name before they are saved to the database.
See Rails Validations for more.