Rails 4 Migration | Add Table with Reference

Question

I am attempting to create a Collaboration table in my Rails 4 project, but I've run into an issue. I wish it to belong_to a single user, the collaborator.

I ran the following command to generate the model and the migration, which I've also copied below.

rails generate model Collaboration project:references collaborator:references accepted:boolean

Migration:

class CreateCollaborations < ActiveRecord::Migration
    def change
        create_table :collaborations do |t|
            t.references :project, index: true, foreign_key: true
            t.references :collaborator, index: true, foreign_key: true
            t.boolean :accepted

            t.timestamps null: false
        end
    end
end

Model:

class Collaboration < ActiveRecord::Base
    belongs_to :project
    belongs_to :collaborator, class_name: 'User'
end

I updated the Collaboration model to include , class_name: 'User' as shown above. Similarly, I updated the existing Strategy model to include a has_many :collaborations

class Project < ActiveRecord::Base
    has_many :collaborations
end

When I run rake db:migrate, I get the following error reported.

rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:

PG::UndefinedTable: ERROR:  relation "collaborators" does not exist

I'm a bit puzzled as to wy this is happening. Any assistance would be greatly appreciated! Thank you. :)

EDIT:

Adding code for my User model as well.

class User < ActiveRecord::Base
    authenticates_with_sorcery!

    has_many :projects
    has_many :collaborations
end

I edited out validations for fields such as password, email, etc to try to remove clutter.

Solution 1

This part of your migration:

t.references :collaborator, index: true, foreign_key: true

will try to create a foreign key inside the database so that the collaborator_id column of the collaborations table will be guaranteed to be NULL or contain the id of a column in the collaborators table. You can't create that FK until the collaborators table exists.

The error you're getting is:

relation "collaborators" does not exist

and that's just telling you that you don't have a collaborators table but you're trying to reference it.

You need a migration to create the collaborators table before you create your collaborations table.

Solution 2

In Rails 5, at least, you can use foreign_key: {to_table: ... }} as follows.

create_table :messages, id: :uuid do |t|
  t.references :from_user, type: :uuid, index: true, null: false, foreign_key: {to_table: :users, on_delete: :cascade}
  t.references :to_user, type: :uuid, references: :user, index: true, null: false, foreign_key: {to_table: :users, on_delete: :cascade}
  t.text :body, null: false
  t.timestamps
end

Solution 3

sorry for being late, but essentially it's all about convenience, remember that's the essence of rails. so; every reference should be targeting the table that should be in the plural (since a table holds many "objects") therefore, you must make the reference to plural so rails will generate a reference to a singular object. button line, your migration should look more like;

class CreateCollaborations < ActiveRecord::Migration
  def change
    create_table :collaborations do |t|
        t.references :projects, index: true, foreign_key: true
        t.references :collaborators, index: true, foreign_key: true
        t.boolean :accepted

        t.timestamps null: false
    end
  end
end

Now, if you follow the conventions, then you should have no problem with the rest, just keep in mind that belong_to is to a singular object and has_many is to a plural object.

PS: I would not use past reference for the column, like accepted

Happy Coding

Comments

[MarsAtomic]

This is what I was thinking as well. Just to clarify, he's aliasing user as collaborator, so he needs to make sure his create_users_xxxxx.rb migration takes place before this create_collaborations_yyyyy.rb migration.

[Michael Fich]

Hmm, I have a users table which was set up earlier in my project. I tried to add a separate migration to add a collaborator reference to the collaborators table however I ran into the same error with that migration as I encountered with the first.

[Michael Fich]

@MarsAtomic - That's exactly right! The issue is because I am trying to reference the users table while aliasing it as "collaborator". Still working through the errors though.

[mu is too short]

So collaborations.collaborator_id is supposed to be a users.id value? How do you feel about using t.references :user instead?

[Michael Fich]

@muistooshort - That's something I could look to use if I can't get this sorted out. I'd like to get it figured out as it's currently constructed first, if possible.

[mu is too short]

As near as I can tell, you can (1) use user_id as the column name (i.e. t.references :user), (2) don't use an FK (i.e. foreign_key: false), or (3) add the database FK by hand with a bit of SQL. (1) is the most Railsy I suppose, (2) is a shortcut to broken data in your database, (3) will require switching your schema.rb to structure.sql. The docs don't seem to offer anything else. I do (3) because I use all kinds of things in the database that AR doesn't understand.