groupProperty not work well

[hackingwu]

I use groupProperty in withCriteria, like this:

{
                    projections {
                        groupProperty("type")
                        property("type")

                        sum("isHUPDAT")//, "numOfHUPDAT")
                        sum("duration")//, "numOfDuration")
//                        countDistinct("logicalLogID") //"count"
                    }
                }

Howerver the group not work well, I turn on the mongo profile to log execution, I found the mongo aggregation statement is

[ { $project: { type: 1, isHUPDAT: 1, duration: 1 } }, { $group: { _id: { type: "$type", _id: "$_id" }, sum_isHUPDAT: { $sum: "$isHUPDAT" }, sum_duration: { $sum: "$duration" } } } ]

Excatly, I just want to group by type, so correct group id should be like this { _id: { type: "$type" }.

So I trace the gorm mongo source code, In grails-datastore-gorm-mongodb-6.1.6.RELEASE org.grails.datastore.mapping.mongo.query.MongoQuery there are codes as following:

        projectProjectionHandlers.put(PropertyProjection.class, new ProjectionHandler() {
            @Override
            public String handle(PersistentEntity entity, Document projectObject, Document groupBy, PropertyProjection projection) {
                String property = projection.getPropertyName();
                projectObject.put(property, 1);
                Document id = getIdObjectForGroupBy(groupBy);
                String projectedValueKey = property.replace('.', '_');
                id.put(projectedValueKey, "$" + property);
                // we add the id to the grouping to make it not distinct
                id.put(MongoEntityPersister.MONGO_ID_FIELD, "$" + MongoEntityPersister.MONGO_ID_FIELD);
                return projectedValueKey;
            }
        });

You will alway and _id if I use group, which will make mistake.

// we add the id to the grouping to make it not distinct
                id.put(MongoEntityPersister.MONGO_ID_FIELD, "$" + MongoEntityPersister.MONGO_ID_FIELD);

I don't know why? is it a bug or how can i do ?

[hackingwu]

If I remove property('type') It seems will not generate id.

[ { $project: { type: 1, isHUPDAT: 1, duration: 1 } }, { $group: { _id: { type: "$type", _id: "$_id" }, sum_isHUPDAT: { $sum: "$isHUPDAT" }, sum_duration: { $sum: "$duration" } } } ]

is groupProperty or perperty handler is wrong?

[hackingwu]

select sum(isHUPDAT), sum(duration) from xxx group by type. how do i write in criteria if I want so.