Element API: Get Matrix Content

Question

So I'm trying to get my Matrix as JSON with the Craft CMS Element API plugin.

<?php

use Craft\elements\Entry;

return [
    'endpoints' => [
        'api/sites' => [
            'elementType' => craft\elements\Entry::class,
            'criteria' => ['section' => 'sites'],
            'elementsPerPage' => 1,
            'transformer' => function(Entry $entry) {
                $matrixBlocks =[];
                foreach ($entry->contentMatrix as $block) {
                    switch ($block->type->handle) {
                        case 'sectionTitleBlock':
                            $matrixBlocks[] = [
                                'content' => $block->sectionTitleBlock
                            ];
                            break;
                    }
                }
                return [
                    'matrix' => $matrixBlocks,
                ];
            },
            'paginate' => false,
            'pretty' => true,
        ],
    ]
];

The error message im getting is

"error": { "code": 2, "message": "Invalid argument supplied for foreach()" }

I think the problem is that $entry->contentMatrix is giving me a MatrixBlockQuery Element.

$sectionTitleBlock is a normal text field

Answer 1

In order to get all related items from a BaseRelationField you'll need this syntax

$entry->getFieldValue('contentMatrix')->all() 

Thus your loop will be

foreach($entry->getFieldValue('contentMatrix')->all() as $block){