Laravel Eloquent : Select random rows on relation based - php

Question

I want to pick questions randomly but category dependent. For example, if the test is given with 10 questions and the total category is 5, the test flow should take 2 questions randomly from each category. Is there a way to select it through random and eloquent relations?
and the question table
+-------+-------+-------+-------+
| id | category_id |.......|
+-------+-------+-------+-------+
already I am using random eloquent but the probability of getting questions from each category is low
public getRandomQuestions($limit)
{
$this->inRandomOrder()->limit($limit)->get()
}
and I'm clueless when it's coming to relations.

Answer 1

You can also use the inRandomOrder and groupBy method together to select random questions from each category.
$questions = Question::with('category')->inRandomOrder()->groupBy('category_id')->limit(2)->get();
This will give you 2 random questions from each category.
You can also use subquery to select questions with certain number of random questions per category
$questions = Question::with('category')
->whereIn('category_id', function($query) use ($limit) {
$query->select('category_id')
->from('questions')
->groupBy('category_id')
->inRandomOrder()
->limit($limit)
})->get();

Answer 2

the query to get 1 random question for each category:
SELECT *
FROM
(SELECT *,
#position := IF(#current_cate=category_id, #position + 1, 1) AS POSITION,
#current_cate := category_id
FROM
(SELECT q.*
FROM category c
INNER JOIN question q ON c.id = q.category_id
ORDER BY RAND()) temp
ORDER BY category_id) temp1
WHERE POSITION <= 2
ORDER BY category_id;
explanation:
since you want the question to be take randomly we need order by rand(), note: inRandomOrder also uses order by rand() under the hood
to be able to get 2 questions for each category, we need a variable (#position) to mark the order of question
laravel implementation:
public getRandomQuestions($limit)
{
$questions = DB::select("SELECT *
FROM
(SELECT *,
#position := IF(#current_cate=category_id, #position + 1, 1) AS POSITION,
#current_cate := category_id
FROM
(SELECT q.*
FROM category c
INNER JOIN question q ON c.id = q.category_id
ORDER BY RAND()) temp
ORDER BY category_id) temp1
WHERE POSITION <= 2
ORDER BY category_id");
return Question::hydrate($questions->toArray());
}

Answer 3

If you're using PHP >= 7.2 the use shuffle()
public function getRandomQuestions($limit) {
return Question::limit($limit)->groupBy('category_id')->get()->shuffle();
}
or else
public function getRandomQuestions($limit) {
return Question::inRandomOrder()->limit($limit)->groupBy('category_id')->get();
}
the trick is you need to use groupBy() clause for this