How to perform Realm count query

问题

How can I do a count query on Realm?

for example this is my model

class Dog: Object {
  dynamic var name = ""
}
class Person: Object {
  dynamic var name = ""

  let dogs = List<Dog>()
}

I want to fetch all persons with at least one dog something like

Realm().objects(Person).filter("dogs.@count > 0")

but @count isn't supported as i understand

回答1:

Yes, Realm still does not support .@count query. You can work around that you modify the Person model to have a count property. Then you update the count property when you append a dog object to the dogs array.

This feature request is tracked by Issue #1166 https://github.com/realm/realm-cocoa/issues/1166

Update

Realm supports @count and other collection queries from v0.96.

回答2:

The syntax for the new aggregate expressions (@count, @min, @max, @sum, @avg) for Results and List looks like this:

realm.objects(Person.self).filter("dogs.@count > 0")

来源：https://stackoverflow.com/questions/31906563/how-to-perform-realm-count-query