diff --git a/django_mongodb/compiler.py b/django_mongodb/compiler.py
index bf2dbc973..d950c8d59 100644
--- a/django_mongodb/compiler.py
+++ b/django_mongodb/compiler.py
@@ -1,6 +1,6 @@
 from django.core.exceptions import EmptyResultSet, FieldDoesNotExist, FullResultSet
 from django.db import DatabaseError, IntegrityError, NotSupportedError
-from django.db.models import NOT_PROVIDED, Count, Expression
+from django.db.models import Count, Expression
 from django.db.models.aggregates import Aggregate
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.sql import compiler
@@ -23,14 +23,21 @@ def execute_sql(
         # QuerySet.count()
         if self.query.annotations == {"__count": Count("*")}:
             return [self.get_count()]
-        # Specify columns if there are any annotations so that annotations are
-        # computed via $project.
-        columns = self.get_columns() if self.query.annotations else None
+
+        columns = self.get_columns()
         try:
-            query = self.build_query(columns)
+            query = self.build_query(
+                # Avoid $project (columns=None) if unneeded.
+                columns if self.query.annotations or not self.query.default_cols else None
+            )
         except EmptyResultSet:
-            return None
-        return query.fetch()
+            return iter([]) if result_type == MULTI else None
+
+        return (
+            (self._make_result(row, columns) for row in query.fetch())
+            if result_type == MULTI
+            else self._make_result(next(query.fetch()), columns)
+        )
 
     def results_iter(
         self,
@@ -43,37 +50,23 @@ def results_iter(
         Return an iterator over the results from executing query given
         to this compiler. Called by QuerySet methods.
         """
-        columns = self.get_columns()
-
         if results is None:
             # QuerySet.values() or values_list()
-            try:
-                results = self.build_query(columns).fetch()
-            except EmptyResultSet:
-                results = []
+            results = self.execute_sql(MULTI, chunked_fetch=chunked_fetch, chunk_size=chunk_size)
 
-        converters = self.get_converters(columns)
-        for entity in results:
-            yield self._make_result(entity, columns, converters, tuple_expected=tuple_expected)
+        fields = [s[0] for s in self.select[0 : self.col_count]]
+        converters = self.get_converters(fields)
+        rows = results
+        if converters:
+            rows = self.apply_converters(rows, converters)
+        if tuple_expected:
+            rows = map(tuple, rows)
+        return rows
 
     def has_results(self):
         return bool(self.get_count(check_exists=True))
 
-    def get_converters(self, expressions):
-        converters = {}
-        for name_expr in expressions:
-            try:
-                name, expr = name_expr
-            except TypeError:
-                # e.g., Count("*")
-                continue
-            backend_converters = self.connection.ops.get_db_converters(expr)
-            field_converters = expr.get_db_converters(self.connection)
-            if backend_converters or field_converters:
-                converters[name] = backend_converters + field_converters
-        return converters
-
-    def _make_result(self, entity, columns, converters, tuple_expected=False):
+    def _make_result(self, entity, columns):
         """
         Decode values for the given fields from the database entity.
 
@@ -82,7 +75,6 @@ def _make_result(self, entity, columns, converters, tuple_expected=False):
         """
         result = []
         for name, col in columns:
-            field = col.field
             column_alias = getattr(col, "alias", None)
             obj = (
                 # Use the related object...
@@ -91,16 +83,7 @@ def _make_result(self, entity, columns, converters, tuple_expected=False):
                 if column_alias is not None and column_alias != self.collection_name
                 else entity
             )
-            value = obj.get(name, NOT_PROVIDED)
-            if value is NOT_PROVIDED:
-                value = field.get_default()
-            elif converters:
-                # Decode values using Django's database converters API.
-                for converter in converters.get(name, ()):
-                    value = converter(value, col, self.connection)
-            result.append(value)
-        if tuple_expected:
-            result = tuple(result)
+            result.append(obj.get(name, col.field.get_default()))
         return result
 
     def check_query(self):