as3io / modlr-persister-mongodb

        $changeset = $model->getChangeSet();

        $update = [];

        foreach ($changeset['attributes'] as $key => $values) {

            if (null === $values['new']) {

                $op = '$unset';

                $value = 1;

            } else {

                $op = '$set';

                $value = $this->getFormatter()->getAttributeDbValue($metadata->getAttribute($key), $values['new']);

            }

            $update[$op][$key] = $value;

        }

        // @todo Must prevent inverse relationships from persisting

        foreach ($changeset['hasOne'] as $key => $values) {

        }

        // @todo Must prevent inverse relationships from persisting

        foreach ($changeset['hasOne'] as $key => $values) {

            if (null === $values['new']) {

                $op = '$unset';

                $value = 1;

            } else {

                $op = '$set';

                $value = $this->getFormatter()->getHasOneDbValue($metadata->getRelationship($key), $values['new']);

            }

            $update[$op][$key] = $value;

        }

        foreach ($changeset['hasMany'] as $key => $values) {

            if (null === $values['new']) {

            $update[$op][$key] = $value;

        }

        foreach ($changeset['hasMany'] as $key => $values) {

            if (null === $values['new']) {

                $op = '$unset';

                $value = 1;

            } else {

                $op = '$set';

                $value = $this->getFormatter()->getHasManyDbValue($metadata->getRelationship($key), $values['new']);

            }

            $update[$op][$key] = $value;

        }

        if (empty($update)) {

            return $model;