Multiselect attribute not showing on frontend when two or more options selected

Question

I have a custom product attribute that uses a multiselect input to select one or more product stockists.

The data is being stored correctly, and selecting 1 option adds the information to the "More information' tab on the product frontend page.

Selecting 2 or more options, the information is no longer visible on the frontend.

Attribute config below

$eavSetup = $this->eavSetupFactory->create(['setup' => $setup]);
$eavSetup->addAttribute(
                \Magento\Catalog\Model\Product::ENTITY,
                'stockist',
                [
                    'type' => 'varchar',
                    'label' => 'Stockist',
                    'input' => 'multiselect',
                    'source' => 'My\Module\Model\Attribute\Source\Stockist',
                    'backend' => 'Magento\Eav\Model\Entity\Attribute\Backend\ArrayBackend',
                    'global' => \Magento\Eav\Model\Entity\Attribute\ScopedAttributeInterface::SCOPE_GLOBAL,
                    'visible' => true,
                    'required' => false,
                    'searchable' => true,
                    'filterable' => true,
                    'comparable' => false,
                    'visible_on_front' => true,
                    'used_in_product_listing' => true
                ]
            );

My\Module\Model\Attribute\Source\Stockist:

namespace My\Module\Model\Attribute\Source;

use My\Module\Model\ResourceModel\Stockist\CollectionFactory;
use Magento\Eav\Model\Entity\Attribute\Source\AbstractSource;

class Stockist extends AbstractSource
{
    private $collectionFactory;

    public function __construct(CollectionFactory $collectionFactory)
    {
        $this->collectionFactory = $collectionFactory;
    }

    public function getAllOptions()
    {
        $stockistCollection = $this->collectionFactory->create();
        $stockistCollection->addFieldToSelect('*')->load();

        $result = [];

        foreach ($stockistCollection as $stockist) {
            $result[] = [
                'value' => $stockist->getId(),
                'label' => $stockist->getName()
            ];
        }

        return $result;
    }
}

Answer 1

Add this method to your Stockist class:

public function getOptionText($value)
{
    $isMultiple = false;
    if (strpos($value, ',')) {
        $isMultiple = true;
        $value = explode(',', $value);
    }

    $options = $this->getAllOptions();

    if (!is_array($value)) {
        $value = [$value];
    }
    $optionsText = [];
    foreach ($options as $item) {
        if (in_array($item['value'], $value)) {
            $optionsText[] = $item['label'];
        }
    }

    if ($isMultiple) {
        return $optionsText;
    } elseif ($optionsText) {
        return $optionsText[0];
    }

    return false;
}

haven't tested it, so watch out for typos and syntax errors.

Off topic things but might help.
You don't need to reload from the db all data each time getAllOptions is called:

class Stockist extends AbstractSource
{
    private $collectionFactory;
    $private $options;

    public function __construct(CollectionFactory $collectionFactory)
    {
        $this->collectionFactory = $collectionFactory;
    }

    public function getAllOptions()
    {
        if ($this->options === null) {
            $stockistCollection = $this->collectionFactory->create();
            $stockistCollection->addFieldToSelect('*')->load();

            $this->options = [];

            foreach ($stockistCollection as $stockist) {
                $this->options[] = [
                    'value' => $stockist->getId(),
                    'label' => $stockist->getName()
                ];
            }
        }
        return $this->options;
    }
}