Rails 4 Migration | Add Table with Reference

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.

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.timestampsend

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  endend

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