Creating a "what's hot" Reddit algorithm with Laravel cover image

Creating a "what's hot" Reddit algorithm with Laravel

Eduar Bastidas • January 9, 2022

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This is a small guide on how to implement a Reddit-style "what's hot" algorithm with Laravel Frameowrk.

There are two primary benefits to using a "what's hot" algorithm.

For this example, we are going to assume that we are running a website that provides users with the functionality to "thumbs up" or "thumbs down" videos that have been submitted.

Our table design.

Note that I am going to try to keep our database design as simple as possible, lest we allow other topics to creep into the article. Here is the structure of an example table. Note that the three columns that are most important to us are "thumbs_up", "thumbs_down" and "created_at" Without these columns, we cannot implement a "what's hot" page:

 1<?php
 2 
 3use Illuminate\Database\Migrations\Migration;
 4use Illuminate\Database\Schema\Blueprint;
 5use Illuminate\Support\Facades\Schema;
 6 
 7class CreateVideosTable extends Migration
 8{
 9    /**
10     * Run the migrations.
11     *
12     * @return void
13     */
14    public function up()
15    {
16        Schema::create('videos', function (Blueprint $table) {
17            $table->id();
18            $table->string('title');
19            $table->string('url');
20            $table->smallInteger('thumbs_up');
21            $table->smallInteger('thumbs_down');
22            $table->timestamps();
23        });
24    }
25 
26    /**
27     * Reverse the migrations.
28     *
29     * @return void
30     */
31    public function down()
32    {
33        Schema::dropIfExists('videos');
34    }
35}

Our SQL query.

Personally, I think that it is better to implement the "what's hot" algorithm in SQL, and not in Laravel directly. i.e. Let the database handle the heavy work. This is because:

  1. It allows us to avail of any indexes that we created.
  2. We can cache the results of the query in memory if we need to.

The query looks like this (based on the Reddit algorithm):

1Video::orderByRaw('
2    LOG10(ABS(thumbs_up - thumbs_down) + 1) *
3    SIGN(thumbs_up - thumbs_down) +
4    (UNIX_TIMESTAMP(created_at) / 300000) DESC
5')->limit(100)->get();

As you can see, the algorithm is implemented in the orderByRaw method and we've limited the results to 100. Let's explain a little bit how the sorting algorithm works.

Let's quickly create a seeder together with a factory to fill our video table:

 1<?php
 2 
 3namespace Database\Factories;
 4 
 5use Illuminate\Database\Eloquent\Factories\Factory;
 6 
 7class VideoFactory extends Factory
 8{
 9    /**
10     * Define the model's default state.
11     *
12     * @return array
13     */
14    public function definition()
15    {
16        return [
17            'title' => $this->faker->sentence,
18            'url' => $this->faker->url,
19            'thumbs_up' => $this->faker->numberBetween(0, 120),
20            'thumbs_down' => $this->faker->numberBetween(0, 120),
21        ];
22    }
23}
 1<?php
 2 
 3namespace Database\Seeders;
 4 
 5use App\Models\Video;
 6use Illuminate\Database\Seeder;
 7 
 8class VideoSeeder extends Seeder
 9{
10    /**
11     * Run the database seeds.
12     *
13     * @return void
14     */
15    public function run()
16    {
17        Video::factory()->count(50)->create();
18    }
19}

After adding a few videos to your table and running the "what's hot" query above, you'll see that a row's total score does not guarantee it the top spot. Instead, our algorithm takes both the record's total score and its creation time into account.

Here is a result obtained in tinker for me (I am using the "what's hot" algorithm):

 1[!] Aliasing 'Video' to 'App\Models\Video' for this Tinker session.
 2=> Illuminate\Database\Eloquent\Collection {#1375
 3     all: [
 4       App\Models\Video {#1743
 5         id: 33,
 6         title: "Voluptatibus autem similique et accusantium eos.",
 7         url: "http://walter.com/sequi-ea-veritatis-est-laudantium-alias-numquam-voluptates",
 8         thumbs_up: 56,
 9         thumbs_down: 3,
10         created_at: "2022-01-09 14:03:47",
11         updated_at: "2022-01-09 22:13:55",
12       },
13       App\Models\Video {#1990
14         id: 35,
15         title: "Numquam molestias sapiente quo corrupti nemo fuga.",
16         url: "http://littel.org/et-facilis-voluptas-rerum",
17         thumbs_up: 76,
18         thumbs_down: 28,
19         created_at: "2022-01-09 23:13:14",
20         updated_at: "2022-01-09 22:13:55",
21       },
22       App\Models\Video {#1991
23         id: 2,
24         title: "Rem sit explicabo harum.",
25         url: "https://www.lang.com/ratione-quia-non-commodi-labore-occaecati-non",
26         thumbs_up: 88,
27         thumbs_down: 59,
28         created_at: "2022-01-08 05:09:10",
29         updated_at: "2022-01-09 22:13:55",
30       },
31       App\Models\Video {#1992
32         id: 43,
33         title: "Minus fugit culpa ut necessitatibus tenetur non.",
34         url: "http://www.ernser.com/",
35         thumbs_up: 51,
36         thumbs_down: 36,
37         created_at: "2022-01-08 04:17:35",
38         updated_at: "2022-01-09 22:13:55",
39       },
40       App\Models\Video {#1993
41         id: 23,
42         title: "Tempora voluptatibus consequatur numquam sequi autem similique voluptatum.",
43         url: "http://friesen.info/",
44         thumbs_up: 93,
45         thumbs_down: 8,
46         created_at: "2022-01-04 23:29:15",
47         updated_at: "2022-01-09 22:13:55",
48       },
49     ],
50   }

If you want to get the source code for this example you can find it here. https://github.com/mreduar/whats-hot-algorithm-with-laravel

Extra Pointers.

If you have any questions or concerns, feel free to post them in the comment section below.