Set constraints on Readouts.user_id foreign key

Add Measurements table

app/controllers/readouts_controller.rb

@@ -6,7 +6,7 @@ class ReadoutsController < ApplicationController
   def new
     @quantities -= @prev_quantities
     # TODO: raise ParameterInvalid if new_quantities.empty?
-    @readouts = current_user.readouts.build(@quantities.map { |q| {quantity: q} })
+    @readouts = @quantities.map { |q| q.readouts.build }
 
     @user_units = current_user.units.ordered
 

app/models/quantity.rb

@@ -6,6 +6,7 @@ class Quantity < ApplicationRecord
   belongs_to :parent, optional: true, class_name: "Quantity"
   has_many :subquantities, ->{ order(:name) }, class_name: "Quantity",
     inverse_of: :parent, dependent: :restrict_with_error
+  has_many :readouts, dependent: :restrict_with_error
 
   validate if: ->{ parent.present? } do
     errors.add(:parent, :user_mismatch) unless user_id == parent.user_id

app/models/readout.rb

@@ -4,4 +4,6 @@ class Readout < ApplicationRecord
   belongs_to :user
   belongs_to :quantity
   belongs_to :unit
+
+  # TODO: validate quantity.user_id == unit.user_id != NULL
 end