M2.1.4 : ArrayBackend cannot save value '0'

[kanduvisla]

When saving a multiselect attribute with value '0', the value gets not saved.

Preconditions

1. Magento 2.1.4

Steps to reproduce

1. Create a mutliselect attribute
2. Set it's source model (in the database to a custom source model.
3. Have this source model return options that have a value of '0'.

For example: a custom source model that returns the list of customer groups including the 'Not Logged In'-group (which has ID 0):

/**
 * @var GroupManagementInterface
 */
protected $groupManagement;

/**
 * CustomerGroup constructor.
 * @param GroupManagementInterface $groupManagement
 */
public function __construct(
    GroupManagementInterface $groupManagement
) {
    $this->groupManagement = $groupManagement;
}

/**
 * @return array
 */
public function toArray()
{
    $notLoggedInGroup = $this->groupManagement->getNotLoggedInGroup();
    $groups = [
        $notLoggedInGroup->getId() => $notLoggedInGroup->getCode()
    ];

    foreach ($this->groupManagement->getLoggedInGroups() as $group) {
        $groups[$group->getId()] = $group->getCode();
    }

    return $groups;
}

Result:

Expected result

1. When I selected the groups, I expect the 'Not Logged In' group to be saved as well

Actual result

1. The 'Not Logged In' group is not saved

The reason

This is because the 'Not Logged In' group has a value of '0' and the \Magento\Eav\Model\Entity\Attribute\Backend\ArrayBackend::beforeSave()-method does the following:

/**
 * Prepare data for save
 *
 * @param \Magento\Framework\DataObject $object
 * @return \Magento\Eav\Model\Entity\Attribute\Backend\AbstractBackend
 */
public function beforeSave($object)
{
    $attributeCode = $this->getAttribute()->getAttributeCode();
    $data = $object->getData($attributeCode);
    if (is_array($data)) {
        $data = array_filter($data);
        $object->setData($attributeCode, implode(',', $data));
    }

    return parent::beforeSave($object);
}

The whole key here is the array_filter-method: this filters out 'falsy' values. '0' is concidered 'falsy', so it's stripped out. Even though we explicitly selected this value.

Workaround

To fix this, explicitly allow string value '0' in array_filter (this is what I'm currently doing in a customer backend model that extends ArrayBackend):

/**
 * @param \Magento\Framework\DataObject $object
 * @return $this
 */
public function beforeSave($object)
{
    $attributeCode = $this->getAttribute()->getAttributeCode();
    $data = $object->getData($attributeCode);
    if (is_array($data)) {
        $data = array_filter($data, function ($value) {
            return $value === '0' || !empty($value);
        });
        $object->setData($attributeCode, implode(',', $data));
    }

    if (!$object->hasData($attributeCode) && $this->getDefaultValue()) {
        $object->setData($attributeCode, $this->getDefaultValue());
    }

    return $this;
}

[nkajic]

@nkajic working on issue

[okorshenko]

@nkajic thank you for the fix
@kanduvisla thank you for reporting the issue