Can a discriminator field ever trigger a duplicate field mapping exception?

[jmikola]

We have this method in ClassMetadataInfo:

public function setDiscriminatorField($discriminatorField)
{
    if ( ! isset($discriminatorField['name']) && isset($discriminatorField['fieldName'])) {
        $discriminatorField['name'] = $discriminatorField['fieldName'];
    }
    if (isset($this->fieldMappings[$discriminatorField['name']])) {
        throw MongoDBException::duplicateFieldMapping($this->name, $discriminatorField['name']);
    }
    $this->discriminatorField = $discriminatorField;
}

Based on how annotations are loaded, the discriminator annotations are processed at the class doc-block level and presumably before any field-level annotations. Therefore, I don't think any field mappings would exist at the time this method is called.

Perhaps it's more relevant for metadata defined in PHP, XML, and YAML?

The example in the annotations reference actually has a field mapping declared on the property corresponding to the discriminator field. That's the very thing I expect would trigger this exception, if the same example was ported to XML or YAML.

[jmikola]

Discriminators were recently refactored in #720 and the exception was kept.