Symfony2 Doctrine get random product from a category

Question

I have the following database scheme:

table 'products'
id
category_id

and of course a category table, just with an id.

The data look something like that:

Products
--------------------
| id | category_id |
--------------------
| 0  | 1           |
| 1  | 1           |
| 2  | 1           |
| 3  | 2           |
| 4  | 2           |
| 5  | 1           |
--------------------

I would like to select a category(for example Category 1), so I select all the rows from that category in my product-repository class:

return $this
    ->createQueryBuilder('u')
    ->andWhere('u.category = :category')
    ->setMaxResults(1)
    ->setParameter('category', $category->getId())
    ->getQuery()
    ->getSingleResult()
;

How I can select now a random product? Also: Is it possible to solve this via Relationships?

I have a OneToMany Relationship between the entities "Category" and "Product", so I could also get all the products via category->getProducts()...

Any help would be really useful, thanks

Answer 1

You first have to count the total number of products, then generate a random offset to select a random product.

This should get you started:

$count = $this->createQueryBuilder('u')
             ->select('COUNT(u)')
             ->getQuery()
             ->getSingleScalarResult();

And then you can generate a random number between your 1 and the total number of rows.

return $this->createQueryBuilder('u')
    ->where('u.category = :category')
    ->setFirstResult(rand(0, $count - 1))
    ->setMaxResults(1)
    ->setParameter('category', $category->getId())
    ->getQuery()
    ->getSingleResult()
;

Which translates to:

SELECT * FROM products WHERE category_id = ? LIMIT 1, {random offset}