When filtering on an attribute of type Object Relation the results are not as expected.

(as in

new Criterion\Field( 'recipient', Criterion\Operator::EQ, $currentUserId )

where 'recipient' is an attribute of datatype 'Object Relation')

This seems to be due to the fact that the searchService only takes into consideration the database fields sort_key_int or sort_key_string (depending onthe datatype).

But in the converter class for Relation the sortKey is hardcoded to "false" which leads to empty entries in the sort_key_int column of ezcontentobject_attribute table rows for Object Relations.

My quick fix was to replace

public function toFieldValue( StorageFieldValue $value, FieldValue $fieldValue )
    {
        $fieldValue->data = array(
            "destinationContentId" => $value->dataInt,
        );
        $fieldValue->sortKey = false;
    }

with

public function toFieldValue( StorageFieldValue $value, FieldValue $fieldValue )
    {
        $fieldValue->data = array(
            "destinationContentId" => $value->dataInt,
        );
        $storageFieldValue->sortKeyInt = (int)$value->sortKey;
    }

which seems to fix the problem. Since i'm no kernel-expert on eZ5 i'm not sure if this is the best solution, though.