How to validate overlapping times in Rails with po

Question

I have an Event model that has start_at time and end_at time in my schedule app and I want to validate the overlapping time before saving.

I create my rails app on Cloud9.

My view image as followings;

Day1
07:00 - 07:20 event1
10:30 - 11:30 event2
15:40 - 16:10 event3
[add event button]

Day2
08:15 - 09:05 event4
12:08 - 13:04 event5
14:00 - 14:25 event6
[add event button]

[save schedule button]

start_at time and end_at time can be changed and added at the same time.

What I'd like to do is to display error if I try to add (or change to) 07:05 - 07:30 for Day1, for example, 13:50 - 14:30 for Day2 and so on.

For example;

app_development=# select * from events;

 id | start_at |  end_at  | title  | detail | schedule_id |         created_at         |         updated_at         
----+----------+----------+--------+--------+-----------------+----------------------------+----------------------------
  1 | 07:00:00 | 07:20:00 | event1 |        |               1 | 2016-04-12 05:28:44.166827 | 2016-04-12 12:52:07.682872
  2 | 10:30:00 | 11:30:00 | event2 |        |               1 | 2016-04-12 05:28:44.17747  | 2016-04-12 12:52:07.689934
  3 | 15:40:00 | 16:10:00 | event3 |        |               1 | 2016-04-12 05:29:07.5005   | 2016-04-12 12:52:07.693477

I added 07:05 - 07:30 above table, but the validation doesn't work.

Although I asked the similar question, I was advised to use postgresql instead of sqlite3.

So I managed to configure postgresql, but the result is the same. It would be appreciated if you could give me how to check and display error.

schema.rb

  create_table "events", force: :cascade do |t|
    t.time     "start_at"
    t.time     "end_at"
    t.string   "title"
    t.integer  "room_id"
    ...

  create_table "rooms", force: :cascade do |t|
    t.string   "room"
    t.integer  "schedule_id"
    ...

  create_table "schedules", force: :cascade do |t|
    t.string   "title"
    t.integer  "user_id"
    t.date     "departure_date"
    ...

Give the following models:

class Event < ActiveRecord::Base
  belongs_to :room, inverse_of: :events
  has_one :schedule, autosave: false, through: :room
  ...
  validate :cannot_overlap_another_event

  def cannot_overlap_another_event
    range = Range.new start_at, end_at
    overlaps = Event.exclude_self(id).in_range(range)
    overlap_error unless overlaps.empty?
  end

  scope :in_range, -> range {
    where('(start_at BETWEEN ? AND ?)', range.first, range.last)
  }
  scope :exclude_self, -> id { where.not(id: id) }

  def overlap_error
    errors.add(:overlap_error, 'There is already an event scheduled in this hour!')
  end

class Schedule < ActiveRecord::Base
  belongs_to :user
  has_many :rooms, inverse_of: :schedule
  accepts_nested_attributes_for :rooms, allow_destroy: true
  ...

class Room < ActiveRecord::Base
  belongs_to :schedule, inverse_of: :rooms
  has_many :events, inverse_of: :room
  accepts_nested_attributes_for :events, allow_destroy: true
  ...

_schedule_form.html.erb

  <%= render 'shared/error_messages', object: f.object %>
  <%= f.label :title %>
  <%= f.text_field :title, class: 'form-control' %>
  <br>
    <%= f.label :departure_date %>
    <div class="input-group date" id="datetimepicker">
      <%= f.text_field :departure_date, :value => (f.object.departure_date if f.object.departure_date), class: 'form-control' %>
      <span class="input-group-addon">
        <span class="glyphicon glyphicon-calendar"></span>
      </span>
    </div>
  <script type="text/javascript">
    $(function () {
      $('#datetimepicker').datetimepicker({format:'YYYY-MM-DD'});
    });
  </script>
  <br>
  <div id="room">
    <%= f.simple_fields_for :rooms do |a| %>
  <div id="room_<%= a.object.object_id %>">
        <p class="day-number-element-selector"><b>Day&nbsp;<%= a.index.to_i + 1 %></b></p>

        <%= a.simple_fields_for :events do |e| %>
          <span class="form-inline">
            <p>
              <%= e.input :start_at, label: false %>&nbsp;&nbsp;&nbsp;-&nbsp;&nbsp;&nbsp;
              <%= e.input :end_at, label: false %>
            </p>
          </span>
          <%= e.input :title, label: false %>
        <% end %>
      </div>

      <%= a.link_to_add "Add event", :events, data: {target: "#room_#{a.object.object_id}"}, class: "btn btn-primary" %>

      <%= a.input :room %>

    <% end %>
  </div>

It would be appreciated if you could give me how to check and display error.

EDIT

edit as followings;

event.rb

scope :in_range, -> range {
  where('(start_at BETWEEN ? AND ? OR end_at BETWEEN ? AND ?) OR (start_at <= ? AND end_at >= ?)', range.first, range.last, range.first, range.last, range.first, range.last)
}

Although it seems to work, this validate doesn't work when I add event on a different day as following id=8. (see created_at and updated_at)

app_development=# select * from events;

id | start_at |  end_at  | title  | detail | room_id |         created_at         |         updated_at         
----+----------+----------+--------+--------+-----------------+----------------------------+----------------------------
  1 | 07:00:00 | 07:20:00 | event1 |        |               1 | 2016-04-12 05:28:44.166827 | 2016-04-12 12:52:07.682872
  2 | 10:30:00 | 11:30:00 | event2 |        |               1 | 2016-04-12 05:28:44.17747  | 2016-04-12 12:52:07.689934
  3 | 15:40:00 | 16:10:00 | event3 |        |               1 | 2016-04-12 05:29:07.5005   | 2016-04-12 12:52:07.693477
  8 | 07:05:00 | 07:10:00 | event4 |        |               1 | 2016-04-15 21:37:58.569868 | 2016-04-15 21:39:27.956737

Answer 1

Your scope is headed in the right direct, but doesn't cover all your cases.

scope :in_range, -> range {
  where('(start_at BETWEEN ? AND ?)', range.first, range.last)
}

In your example, you end up checking start_at BETWEEN 7:05 AND 7:30, but start_at on Day 1 is 7:00, which is outside that range.

There are four cases you need to handle:

New range overlaps start
Existing:     |------------|
New:      |-------|

New range overlaps end
Existing: |------------|
New:               |-------|

New range inside existing range
Existing: |------------|
New:         |-------|

Existing range inside new range
Existing:    |-------|
New:      |------------|

Looking, you can see that the first three cases are handled by checking if

new_start BETWEEN start_at AND end_at
OR
new_end   BETWEEN start_at AND end_at

Then you just need to catch the fourth case by adding

OR
start_at BETWEEN new_start AND new_end

You could add a similar check on end_at for code symmetry, but it's not strictly necessary.

Answer 2

You don't need to reinvent the wheel in PostgreSQL, there are two implemented simple methods to achieve overlap checks:

1. SQL's OVERLAPS operator:

Simple enough,

where("(start_at, end_at) OVERLAPS (?, ?)", range.first, range.last)

However this enables one range to be exactly after the other
(in other words, it checks start <= time < end).

2. Range types' && (overlaps) operator:

This is simple too, usually. But PostgreSQL doesn't have a built-in range type for time (however there are tsrange, tstzrange, and daterange for the other temporal types).

You need to create this range type for yourself:

CREATE TYPE timerange AS RANGE (subtype = time);

But after this, you can check overlapping with

where("timerange(start_at, end_at) && timerange(?, ?)", range.first, range.last)

Pros of range types:

• you can control yourself, how do you want to handle range boundaries

  f.ex. you could use timerange(start_at, end_at, '[]') to include both the start & the end-point of the ranges. By default it includes the start, but excludes the end-point of the ranges.

• it can be indexed, f.ex. with

  CREATE INDEX events_times_idx ON events USING GIST (timerange(start_at, end_at));
  

• Exclusion constraints: this is essentially the same, what you want to achieve, but it will be enforced at DB level (like, UNIQUE or any other constraints):

  ALTER TABLE events
    ADD CONSTRAINT events_exclude_overlapping
    EXCLUDE USING GIST (timerange(start_at, end_at) WITH &&);