Magento – Magento2 addAttributeToFilter not working with Multi Select Attribute

At the end I used a default multi-select attribute. With that solution we miss a bit of flexibility, but since the subviews don't change thát often it isn't a problem.

• The default attribute uses indexes, which is fast
• The default attribute is compatible with the SOLR backend

From what I understand you want to send 2 or more values and filter by them using OR.
Something like this:

...
WHERE
    FIND_IN_SET($v1, `some_field`) OR
    FIND_IN_SET($v2, `some_field`) OR
...

$v1 & $v2 are the values of your checkboxes

For that you need to pass to the addAttributeToFilter and array of arrays.

->addAttributeToFilter(
    array(
          array('attribute'=>'some_attribute', 'finset'=>$v1),
          array('attribute'=>'some_attribute', 'finset'=>$v2),
    )
);

Here is a possible implementation.

$data = THE ARRAY OF THE CHECKBOX VALUES;

$filter = array();
foreach ($data as $value) {
    $filter[] = array(
        'attribute' => $attribute->getAttributeCode(),
        'finset'    => $value
    );
}

if (count($filter) > 0) {
    $collection->addAttributeToFilter($filter);
}