support getting count without querying

corehq/apps/dump_reload/sql/filters.py

@@ -12,6 +12,9 @@ def get_filters(self, domain_name):
         of the others."""
         raise NotImplementedError()
 
+    def count(self, domain_name):
+        return None
+
 
 class SimpleFilter(DomainFilter):
     def __init__(self, filter_kwarg):
@@ -40,6 +43,9 @@ class UsernameFilter(DomainFilter):
     def __init__(self, usernames=None):
         self.usernames = usernames
 
+    def count(self, domain_name):
+        return len(self.usernames) if self.usernames is not None else None
+
     def get_filters(self, domain_name):
         """
         :return: A generator of filters each filtering for at most 500 users.
@@ -61,6 +67,9 @@ def __init__(self, field, ids):
         self.field = field
         self.ids = ids
 
+    def count(self, domain_name):
+        return len(self.get_ids(domain_name))
+
     def get_ids(self, domain_name):
         return self.ids
 
@@ -97,7 +106,10 @@ def _base_queryset(self):
         return objects.using(self.db_alias).order_by(self.model_class._meta.pk.name)
 
     def querysets(self):
-        return self._base_queryset()
+        yield self._base_queryset()
+
+    def count(self):
+        return sum(q.count() for q in self.querysets())
 
     def iterators(self):
         for queryset in self.querysets():
@@ -115,11 +127,17 @@ def __init__(self, model_label, filter):
     def build(self, domain, model_class, db_alias):
         return self.__class__(self.model_label, self.filter).prepare(domain, model_class, db_alias)
 
+    def count(self):
+        count = self.filter.count(self.domain)
+        if count is not None:
+            return count
+        return super(FilteredModelIteratorBuilder, self).count()
+
     def querysets(self):
         queryset = self._base_queryset()
         filters = self.filter.get_filters(self.domain)
-        for filter in filters:
-            yield queryset.filter(filter)
+        for filter_ in filters:
+            yield queryset.filter(filter_)
 
 
 class UniqueFilteredModelIteratorBuilder(FilteredModelIteratorBuilder):