How to perform calculation in rails model?

Question

I have created project, stage, task and sub_task scaffolds:

project has a one-to-many association with stage
stage has a one-to-many association with task
task has one-to-many association with sub_task.

stage, task, and sub_task tables have all a field planned_end_date and status.

Now I want to print the total stages, tasks, sub_tasks that aren't completed until planned_end_date for each project in the projects#index action.

How can I do that in a Rails model?

class Project < ApplicationRecord
  has_many :stages, dependent: :destroy
  validate :end_after_start

  private
  def end_after_start
    return if to_date.blank? || form_date.blank?

    if to_date < form_date
      errors.add(:to_date, "Project end date must be same or after the start date")
    end
  end
end

what i have tried-

project#index.html.erb

      <% @projects.each do |project| %>
        <tr>
          <td><%= project.project_name %></td>

          <%  @stages = Stage.where(project_id: @projects.ids) %>
          <%  @tasks = Task.where(stage_id: @stages.ids) %>
          <%  @sub_tasks = SubTask.where(task_id: @tasks.ids) %>

          <%  stage_counter = 0 %>
          <%  task_counter = 0 %>
          <%  sub_task_counter = 0 %>

          <%  @stages.each{|s| stage_counter += 1 if s.planned_end_date.past? && s.status == 0 || s.planned_end_date.past? && s.status == 2} %>
          <%  @tasks.each{|s| task_counter += 1 if s.planned_end_date.past? && s.status == 0 || s.planned_end_date.past? && s.status == 2} %>
          <%  @sub_tasks.each{|s| sub_task_counter += 1 if s.planned_end_date.past? && s.status == 0 || s.planned_end_date.past? && s.status == 2} %>

          <% @count =0 %>
          <%  @count = stage_counter + task_counter + sub_task_counter %>

          <td><span class="alert"><%= @count.to_s + " Activity Pending" %></span></td>

what is code does is prints total number of pending stages, tasks and sub_tasks for all projects and prints same count for every project. I want to print pending stages+tasks+sub_tasks for every project's total pending stages+tasks+sub_tasks. what

SteveTurczyn · Accepted Answer · 2020-03-09 08:21:10Z

Yes, you're counting for ALL projects, not just for the current project.

What you want is...

<% stages = Stage.where(project_id: project.id) %>

note we're using project.id which references the current project in the each loop, not @projects which is all projects.

Better might be...

<% stages = project.stages %>

And better from a performance standpoint is to let the database give you the count...

<% stage_counters = project.stages.where('planned_end_date < ?', Date.today).where(status: [0,2]).count %>

If you're going to do complex boolean tests, it helps to use brackets to ensure you've got the correct order of precedence,

<%  @stages.each{|s| stage_counter += 1 if (s.planned_end_date.past? && s.status == 0) || (s.planned_end_date.past? && s.status == 2)} %>

You can do similar with tasks and sub-tasks by defining the relationship in the model...

has_many :stages, dependent: :destroy
has_many :tasks, through: :stages
has_many :sub_tasks, through: :tasks

This will let you do project.tasks and project.sub_tasks

Note that you may want to move these calculations into the model...

class Project

  def incomplete_stages_count
    stages.where('planned_end_date < ?', Date.today).where(status: [0,2]).count
  end

Which is better, and will let you do...

<% project.incomplete_stages_count %>

but even then it means the Project model needs to know what makes a stage incomplete, which is a headache if you ever change the business rules, so maybe create a scope in Stage

class Stage
  scope :incomplete, -> {where('planned_end_date < ?', Date.today).where(status: [0,2])}
end

And in Project

class Project
  def incomplete_stages_count
    stages.incomplete.count
  end
end

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