Rails 5.2 migrations conundrum, create primary key and foreign keys - mysql

Question

I cannot figure out what is wrong with my migrations, but they won't work, trying to add foreign key on products from primary key in categories
20180724203015_create_categories.rb
class CreateCategories < ActiveRecord::Migration[5.2]
def change
create_table :categories, id: false do |t|
t.string :name
t.text :description
t.integer :category_id, primary_key: true, auto_increment: true
t.timestamps
end
end
end
20180724203105_create_products.rb
class CreateProducts < ActiveRecord::Migration[5.2]
def change
create_table :products do |t|
t.string :name
t.references :category_id, foreign_key: true, index: true
t.timestamps
end
end
end
however this always ends with an error, cannot add foreign key contraint

Answer 1

Ruby on Rails embraces the convention over configuration principle. That means if you follow the Rails conventions things will be much easier and almost no configuration is needed.
In your migrations you decided to fight one of the Rails conventions: The primary key of a database is stored in an id column. When you decide to not follow this convention then you cannot simply use the references method anymore without telling Rails how you set up your database instead.
My advice is: Unless you have a very, very good reason, do not fight against Rails conventions. It will not only make this task (database migration) more complex, but it also increased the risk that something else needs more configuration (ActiveRecord models for example) or that things might break in gems or when you update Rails to a newer version.
That said: Change your migration to use the Rails conventions:
# 20180724203015_create_categories.rb
class CreateCategories < ActiveRecord::Migration[5.2]
def change
create_table :categories do |t| # <- create an `id` column per default
t.string :name
t.text :description
t.timestamps
end
end
end
# 20180724203105_create_products.rb
class CreateProducts < ActiveRecord::Migration[5.2]
def change
create_table :products do |t|
t.references :category, foreign_key: true # <- just name the relation
t.string :name
t.timestamps
end
end
end

Answer 2

The answer to this is to remove t.integer :category_id, and rely on rails' :id column for each table, references can be made with #category or with #product, and as mentioned in the comments - #category = Cateogory.find(params[:id]) or Category.find(params[:category_id]) as I believe that is how it is referenced in routes. Thank you.