Associations between classes

Association rails, associations in rails is sometimes a hard concept to wrap peoples head around but I’ll try to simplify.

Let us imagine we are building a pizza delivery application where our user class carries the users name and address and where pizza has different variation of pizzas. We create our models by running

rails g model pizza pizza:

rails g model user name: address:

Then the next step is to make a single source of truth.

Currently our models have no relation. However now when we create our joiner class, which will be Order class. Our order has to know our pizzas and users, so we generate a model

rails g model Order user:references pizza:references

when we create our attributes with references, rails does a bit of its magic and allows us to access information from different classes now let’s say we wanted to create a list of all the user is associated with we will be able to access @instance_variable.pizzas. we would be able to because we have not created our relationships.

So now we create the relation between the single source of truth and the the other class. which involves us having to go into the models and explicitly state the relation between models.

class Pizza

has_many :orders

has_many :users, through: :orders

end

class Order

belongs_to :pizza

belongs_to :user

end

class User

has_many :orders

has_many :pizzas, through: :orders

end

Make sure that when you create the relations that the other models are associated plural and now users will be able to get information that isn't from the user original class.