CODEWITHSUNDEEP
ruby-on-rails
Abdul Ahmad
Abdul Ahmad

Reputation: 10021

rails creating relationships between 2 existing models

I have 2 models:

Account
Profile

creating these models created 2 tables in the database:

accounts
profiles

now I want to add a relationship:

I ran the following command:

rails g migration AddAccountToProfiles account:references

which created the following migration:

class AddAccountToProfiles < ActiveRecord::Migration
  def change
    add_reference :profiles, :account, index: true, foreign_key: true
  end
end

now I'm a little confused:

why does the migration say :profiles and :account? Shouldn't it be :accounts (plural)?

also, after (or before) creating this migration, I have to add belongs_to and has_many in the appropriate model class right?

as a side question, is there a way to add belongs_to and has_many in the models, and from that information have rails generate the appropriate migration without me manually creating a migration with the 'rails g migration ...' command?

Upvotes: 4

Views: 4002

Answers (2)

chrismanderson
chrismanderson

Reputation: 4813

The migration is correct, because a profile only belongs to one account. It should not be 'accounts'. The migration will place a account_id column onto the profiles table in order to make that connection.

After the migration, you still need to add has_many and belongs_to. In Rails, when defining a relationship, there are generally two steps 1) create the database migration 2) define the relation on the model class itself. You need to have both. In this case, Rails is looking for the account_id column on a profile (the default foreign key) to make the relationship between the two models.

And as for your last question, no, there is not a way to generate migrations after defining a has_many. You can use Rails generators to create the model itself rails generate model ModelName and define the relationship in that model; that will add the correct belongs_to and has_many into the generated model along with the migration. But in practice, it's generally better to create the migration and manually add belongs_to and has_many as needed so there's less of a chance of missing something.

Upvotes: 1

lusketeer
lusketeer

Reputation: 1930

As per rails documentation, the command 

rails g migration AddAccountToProfiles account:references

will generate the migration file below

class AddAccountToProfiles < ActiveRecord::Migration
  def change
    add_reference :profiles, :account, index: true, foreign_key: true
  end
end

Since you specified account:references, then it assumes to create account_id on profiles table, but you still need to add the relationships in the corresponding model files.

When we use :accounts in migration file, it's referring to the table in the database, :account is used as the name of the foreign key to be added onto the table along with suffix _id

Also relevant information here

Upvotes: 4

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