Laravel/Eloquent whereHas with all items in relation?

Question

Models Song and Writer

And I want to query songs such that I only get songs where ALL its writers have a certain field that is true, what would my solution be?

The Laravel whereHas function will get all songs that have at least one writer with that field, like so.

Song::whereHas('writers', function($query){
    $query->where('writerField', '=', true);
});

But what is the pure eloquent way to make sure ALL writer related to a Song has that 'writerField' set to true?

Answer 1

Invert your constraint, and pass the desired count to the whereHas method:

Song::whereHas('writers', function() {
    $query->where('writerField', false);
}, '=', 0);