has_many, belongs_to relation in active record migration rails 4

Question

I have a User model and a Task model. I have not mentioned any relation between them while creating them.

I need to establish that U

Answer 1

To answer the question, "What would be the migration generation command for establishing that relation?"( Meaning, how do you add a migration for existing models with a relationship like User has_many Tasks & Task belongs_to User)

The the easiest way for me to remember is like this:

>rails g migration AddUserToTask user:belongs_to

or

>rails g migration AddUserToTask user:references

:belongs_to is just an alias of :references, so either will do the same thing.

Doing it this way, the command will infer the name of the table from the migration name, set up a change method that will add the column for relationship, and configure it to be indexed:

class AddUserToTask < ActiveRecord::Migration
  def change
    add_reference :tasks, :user, index: true
  end
end

After generating that you:

>rake db:migrate

Finally, you still have to add the usual relations to your models, as is stated in the other answers, but I think this is the right answer to your question.