[web2py] How to select(count<1, groupby=db.person) or how to find persons with no dogs/less than x dogs.

[François Delpierre]

So, for instance :
db().select(db.person.name, db.person.id.count(), groupby=db.person.id, 
left=db.dog.on(db.person.id==db.dog.person_id))

will give me the person, and the number of dogs that this person has.
But I only want to get persons with no dogs.

Regards,

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