I am currently working on my first Ruby/Sinatra Application for my online software engineering program. I wanted to share what I learned about Active Record Associations and all the built in methods we get access to using it.
has_many
An instance of one class that owns many instances of another class. This class must pluralize the has many instance method to get access to all the instances it owns. A User has many recipes
class Actor < ActiveRecord::Base
has_many :characters
end
class Show < ActiveRecord::Base
has_many :characters
end
The has_many association gives us access to 17 methods
actors
actors<<(object, ...)
actors.delete(object, ...)
actors.destroy(object, ...)
actors=(objects)
actor_ids
actor_ids=(ids)
actors.clear
actors.empty?
actors.size
actors.find(...)
actors.where(...)
actors.exists?(...)
actors.build(attributes = {})
actors.create(attributes = {})
actors.create!(attributes = {})
actors.reload
belongs_to
An instance that is owned by the has many class. We will state the belongs to method as singular to retrieve the relationship to the unique owner class. A Recipe belongs to one owner
class Character < ActiveRecord::Base
belongs_to :actor
belongs_to :show
end
To ensure reference consistency, add a foreign key to the owner column of the owned table migration.
class CreateRecipes < ActiveRecord::Migration[6.1]
def change
create_table :characters do |t|
t.belongs_to :actor
t.belongs_to :show
end
end
end
The belongs_to association gives us access to 8 methods
character
character=(character)
build_character(attributes = {})
create_character(attributes = {})
create_character!(attributes = {})
reload_character
character_changed?
character_previously_changed?
has_many through:
This creates a relationship bridge between two owner classes' and the owned/connecting class
class Show < ActiveRecord::Base
has_many :characters
has_many :actors, through: :characters
end
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