如何在Rails中为模型属性创建迁移

Question

I'm having difficulty with bulding attributes within my model. I keep seeing this error

NoMethodError: undefined method `users' for #<ActiveRecord::ConnectionAdapters::SQLite3::TableDefinition:0x00007f9d9ad9df98>

I need attributes that look like this:

#group.rb

class Spree::Group < ActiveRecord::Base
    has_many :users
end

#user_decorator.rb
Spree::User.class_eval do
  belongs_to :group, class_name: "Spree::Group"
end

For group.rb I ran

rails g model Spree::Group

and I got:

class Spree::Group < ApplicationRecord
  has_many :users
end

I'm confused on how to add 'has_many :users' without actually going into the model and inputting it there.

For the user_decorator I'm not sure what that migration would look like. Any help would be fantastic!

Answer 1

You could call:

rails g model group user:references

which will generates an user_id column in the groups table and will modify the group.rb model to add a belongs_to :user relatonship. Please note, you must to put manually the has_many :groups or has_one :group relationship to the user.rb model.

If you already have the model generated, you could create a migration with the following:

rails g migration AddUserToGroup user:belongs_to which will generate:

class AddUserToGroup < ActiveRecord::Migration
  def change
    add_reference :groups, :user, index: true
  end
end

the only difference with this approach is, the belongs_to :user relationship in the group.rb model won't be created automatically, so you must create it for your own.