Replace Complex Creation with Factory Method

Bad Smell

class InvoicesController < ApplicationController
  def create
    @invoice = Invoice.new(params[:invoice])
    @invoice.address = current_user.address
    @invoice.phone = current_user.phone
    @invoice.vip = (@invoice.amount > 1000)

    if Time.now.day > 15
      @invoice.delivery_time = Time.now + 2.month
    else
      @invoice.delivery_time = Time.now + 1.month
    end

    @invoice.save
  end
end

The logic to create an invoice is too complex, it makes InvoicesController a bit difficult to read. And the controller should not know too much things about how to create a model, we should move the the logic of creating an invoice into the Invoice model.

Refactor

class Invoice < ActiveRecord::Base
  def self.new_by_user(params, user)
    invoice = self.new(params)
    invoice.address = user.address
    invoice.phone = user.phone
    invoice.vip = (invoice.amount > 1000)

    if Time.now.day > 15
      invoice.delivery_time = Time.now + 2.month
    else
      invoice.delivery_time = Time.now + 1.month
    end
  end
end

class InvoicesController < ApplicationController
  def create
    @invoice = Invoice.new_by_user(params[:invoice], current_user)
    @invoice.save
  end
end

Now we define a new_by_user method in Invoice model, it takes charge of the invoice creation. So the InvoicesController can just call the new_by_user method to build the invoice object.

Keep in mind the principle "Skinny Controller, Fat Model"