Laravel query builder - how to filter by relationship field

Question

For the sake of example, say I have the following, where there is a relationship set up for each person having one hat.

$people = People::join('hat')->get();

How do I filter my results to only give me the people whose hats are red?

I have tried,

$people = People::join('hat')
    ->where('hat.colour', 'red')
    ->get();    

...but no luck so far.

Cheers

Answer 1

Use whereHas():

$people = People::whereHas('hat', function($query) {
    $query->where('colour', 'red');
})->get();