Selecting random results within Doctrine

Question

I'm new to Doctrine and had a hard time deciding how to get random rows within it without creating custom DQL functions or using a native query. The solution I have come up with is below. This is within a custom repository for an Entity. I'm hoping for some constructive criticism in regards to it, however it currently is working.

class MyRepository extends EntityRepository
{
/**
 * @param int $numberOfResults
 * @return array
 */
public function getRandomResults($numberOfResults = 1)
{
 $maxID = $this->getMax();
 $count = 0;
 $randomNumberCounter = 0;
 $randomNumbers = array();
 while ($randomNumberCounter < $numberOfResults) {
 $randomNumberCounter++;
 $randomNumbers[] = $this->getRandom(0, $maxID);
 }
 $qb = $this->createQueryBuilder('r');
 while ($count < $numberOfResults) {
 $qb
 ->andWhere(
 $qb->expr()->orX(
 // the greater than is to account for holes within the primary key
 $qb->expr()->gte("r.id", "?".$count),
 /* the less than is in case we have a beginning database with a large disparity
 between starting and ending ID */
 $qb->expr()->lte("r.id", "?".$count)
 )
 );
 $count++;
 }
 $result = $qb
 ->setParameters($randomNumbers)
 ->setMaxResults($numberOfResults)
 // ensure we have no duplicates
 ->groupBy('r.id')
 ->getQuery();
 return $result->getResult();
}
/**
 * get the maximum ID that the table has
 * @return mixed
 * TODO: Create a Cron job to set this every 6 hours
 */
public function getMax()
{
 $maxID = $this->createQueryBuilder('r')
 ->select('(MAX(r.id))')
 ->getQuery()
 ->getSingleScalarResult();
 return $maxID;
}
/**
 * @param $min
 * @param $max
 * @return int
 */
public function getRandom($min, $max)
{
 return mt_rand($min, $max);
}
}

• Mathieu Guindon: Welcome to Code Review! Good thing your code works, it's a prerequisite for code that's ready for a peer review ;-)
• talibe: The problem with your code is that the ID is supposed to begin from 0 and will not work if you delete some rows in the database.
• Jonathan K.: @talibe, where do you see this starting from 0? I also believe the < and > filters allow for gaps. Either way, I have a more performant method that I will update this with.
• talibe: If in the table you delete some rows the database will not reorder the IDs. So if you delete the row where id=1, there will be no row corresponding for id=1 any more. Your code will try to find that row and it won't work.

Answer 1

Increment operator ➕➕ can be moved up after usage in while loop

In the first while loop to add numbers to $randomNumbers the value of $randomNumberCounter is incremented on a separate line:

$randomNumberCounter++;

That operation could be combined in the condition of the while loop:

while ($randomNumberCounter++ < $numberOfResults) {
 $randomNumbers[] = $this->getRandom(0, $maxID);
}

There are simpler ways to add numbers in a loop

The block to add to $randomNumbers could be simplified. Instead of using the while loop a for loop could be used:

for($randomNumberCounter = 0; $randomNumberCounter < $numberOfResults; $randomNumberCounter++) {
 $randomNumbers[] = $this->getRandom(0, $maxID);
}

A foreach loop could also be used with range() function:

foreach(range(1, $numberOfResults) as $i) {
 $randomNumbers[] = $this->getRandom(0, $maxID);
}

While it may be the least efficient, a functional approach could be used to assign the array in a single statement using array_fill() and array_map():

$randomNumbers = array_map(
 fn($number) => $this->getRandom(0, $maxID),
 array_fill(0, $numberOfResults, 0)
);

Current approach does not ensure all random numbers will be unique

Perhaps it would be better to ensure that a random number is not already in the array of random numbers before adding it to the array.

Add spaces around boolean operators for readability

Adhering to a standard is not required but it does help with readability when the style is consistent. Many PHP developers follow PHP Standards Recommendations like PSR-12. While it wasn't approved until 2019, PSR-12 replaced PSR-2 which was approved in 2012.

In PSR-12 is section 6 concerning Operators

6.2. Binary operators

All binary arithmetic, comparison, assignment, bitwise, logical, string, and type operators MUST be preceded and followed by at least one space:

if ($a === $b) {
 $foo = $bar ?? $a ?? $b;
} elseif ($a > $b) {
 $foo = $a + $b * $c;
}

Some binary operators in the code above are preceeded and followed by a space - e.g.

$maxID = $this->getMax();

However, other places do not- e.g.

$qb->expr()->gte("r.id", "?".$count),

Since double quotes are used $count could be moved into the string, since variables are parsed within double-quoted strings¹ which would eliminate the need to append with .:

$qb->expr()->gte("r.id", "?$count"),