how to update database schema after running migrations in ruby on rails

I'm starting with Ruby on Rails and I have these two models:

City and Street,

These two models were generated independently with no relation between them. Now I need a city to have many streets and each street to belong to a single city. I ran this command:

bin/rails generate migration AddCityRefToStreets city:references

That generated this migration:

class AddCityRefToStreets < ActiveRecord::Migration[5.2]
  def change
    add_reference :streets, :city, foreign_key: true
  end
end

Then I ran bin/rails db:migrate and then I went into these model classes and wrote:

class City < ApplicationRecord
   has_many :streets, dependant: :destroy
end

and

class Street < ApplicationRecord
   belongs_to :city
end

Rails did not show any complains, and so far it works fine for me. If I ask @city.streets.length it will return the correct amount of streets for that @city. If I ask @street.city it returns the correct city as well.

The thing is, I went into the database using DBeaver and the migration did not generate relations between the cities and streets tables. The streets table shows me a city_id field, but still not showing any relationship in the ER Diagram view.

My question is: what am I missing here? Is this the correct way to relate two entities created independently?

I'm using Linux Mint 18.3, Rails 5.2.1, Sqlite 3.11.0 and DBeaver 5.1.

Solution

The add_reference migration command will have added a city_id column to your streets table.

When you call @city.streets, it is evaluated as the equivalent of Street.where(city_id: @city.id).

Similarly, @street.city will look at the ID stored in city_id column, and do a lookup - the equivalent of City.find(@street.city_id).