query_people_count() implementation and test

src/people.rs

@@ -688,6 +688,7 @@ pub trait ContextPeopleExt {
     fn get_person_id(&self, person_id: usize) -> PersonId;
     fn index_property<T: PersonProperty + 'static>(&mut self, property: T);
     fn query_people<T: Query>(&self, q: T) -> Vec<PersonId>;
+    fn query_people_count<T: Query>(&self, q: T) -> usize;
     fn match_person<T: Query>(&self, person_id: PersonId, q: T) -> bool;
 }
 
@@ -863,6 +864,18 @@ impl ContextPeopleExt for Context {
         accumulator.people
     }
 
+    fn query_people_count<T: Query>(&self, q: T) -> usize {
+        // Special case the situation where nobody exists.
+        if self.get_data_container(PeoplePlugin).is_none() {
+            return 0
+        }
+
+        T::setup(self);
+        let mut accumulator = PeopleAccumulatorCount::default();
+        self.query_people_internal(&mut accumulator, q.get_query());
+        accumulator.count
+    }
+
     fn match_person<T: Query>(&self, person_id: PersonId, q: T) -> bool {
         T::setup(self);
         // This cannot fail because someone must have been made by now.
@@ -1490,6 +1503,23 @@ mod test {
         assert_eq!(people.len(), 0);
     }
 
+    #[test]
+    fn query_people_count() {
+        let mut context = Context::new();
+        let _ = context
+            .add_person((RiskCategoryType, RiskCategory::High))
+            .unwrap();
+
+        assert_eq!(context.query_people_count((RiskCategoryType, RiskCategory::High)), 1);
+    }
+
+    #[test]
+    fn query_people_count_empty() {
+        let context = Context::new();
+
+        assert_eq!(context.query_people_count((RiskCategoryType, RiskCategory::High)), 0);
+    }
+
     #[test]
     fn query_people_macro_index_first() {
         let mut context = Context::new();