Fix migration of default quantities

Allow Quantity formula to be nil but not blank
Add computed energy quantity
Reverse default quantities deletion order

app/controllers/quantities_controller.rb

@@ -59,6 +59,7 @@ class QuantitiesController < ApplicationController
   private
 
   def quantity_params
+    params[:quantity].delete(:formula) if params[:quantity][:formula].blank?
     params.require(:quantity).permit(
       :domain,
       :parent_id,

app/models/quantity.rb

@@ -15,7 +15,7 @@ class Quantity < ActiveRecord::Base
   validate if: -> { parent.present? } do
     errors.add(:parent, :parent_domain_mismatch) unless domain == parent.domain
   end
-  validates :formula, formula: true
+  validates :formula, formula: {allow_nil: true}
 
   after_initialize do
     if new_record?

db/migrate/002_load_defaults.rb

@@ -1,4 +1,5 @@
 class LoadDefaults < ActiveRecord::Migration
+  def change
     reversible do |dir|
       dir.up do
         Unit.create project: nil, shortname: "g", name: "gram"
@@ -13,7 +14,7 @@ class LoadDefaults < ActiveRecord::Migration
         e = Quantity.create project: nil, domain: :diet, parent: nil, name: "Energy",
           description: "Total energy", primary: true
 
-      Quantity.create project: nil, domain: :diet, parent: nil, name: "Proteins",
+        p = Quantity.create project: nil, domain: :diet, parent: nil, name: "Proteins",
           description: "Total amount of proteins", primary: true
 
         f = Quantity.create project: nil, domain: :diet, parent: nil, name: "Fats",
@@ -121,13 +122,20 @@ class LoadDefaults < ActiveRecord::Migration
         v21 = Quantity.create project: nil, domain: :diet, parent: v1, name: "Vitamin K",
           description: ""
 
+        # Calculated quantities go at the and to make sure dependencies exist
+        e1 = Quantity.create project: nil, domain: :diet, parent: e, name: "Calculated",
+          description: "Total energy calculated from macronutrients", primary: true,
+          formula: "4*Proteins + 9*Fats + 4*Carbohydrates"
+
         Source.create project: nil, name: "nutrition label",
           description: "nutrition facts taken from package nutrition label"
       end
+
       dir.down do
-      Unit.where(project: nil).delete_all
-      Quantity.where(project: nil).delete_all
         Source.where(project: nil).delete_all
+        Quantity.where(project: nil).delete_all
+        Unit.where(project: nil).delete_all
+      end
     end
   end
 end

lib/body_tracking/formula.rb

@@ -7,7 +7,7 @@ module BodyTracking
     class InvalidFormula < RuntimeError; end
     class Formula
       def initialize(project, formula)
-        @project = project
+        @project_quantities = Quantity.where(project: project)
         @formula = formula
         @paramed_formula = nil
         @quantities = nil
@@ -79,7 +79,7 @@ module BodyTracking
 
         # 4th: check if identifiers used in formula correspond to existing quantities
         identifiers.uniq!
-        quantities = @project.quantities.where(name: identifiers)
+        quantities = @project_quantities.where(name: identifiers)
         quantities_names = quantities.pluck(:name)
         (identifiers - quantities_names).each do |q|
           errors << [:unknown_quantity, {quantity: q}]