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

There is no special migration command that would be used.

In your User model you will put

class User < ActiveRecord::Base
  has_many :tasks
end

class Task < ActiveRecord::Base
  belongs_to :user
end

In the corresponding migration file for the tasks you have the following field added user_id

Take a look at this guide