php - How to Merge Two Eloquent Collections?

Question

I have a questions table and a tags table. I want to fetch all questions from tags of a given question. So, for example, I may have the tags "Travel," "Trains" and "Culture" attached to a given question. I want to be able to fetch all questions for those three tags. The tricky, so it seems, is that questions and tags relationship is a many-to-many defined in Eloquent as belongsToMany.

I thought about trying to merge the questions Collections as below:

foreach ($question->tags as $tag) {
    if (!isset($related)) {
        $related = $tag->questions;
    } else {
        $related->merge($tag->questions);
    }
}

It doesn't seem to work though. Doesn't seem to merge anything. Am I attempting this correctly? Also, is there perhaps a better way to fetch a row of rows in a many-to-many relationship in Eloquent?

Answer 1

The merge method returns the merged collection, it doesn't mutate the original collection, thus you need to do the following

$original = new Collection(['foo']);

$latest = new Collection(['bar']);

$merged = $original->merge($latest); // Contains foo and bar.

Applying the example to your code

$related = new Collection();

foreach ($question->tags as $tag)
{
    $related = $related->merge($tag->questions);
}