fix array index lookup

Author: timgraham

django_mongodb/features.py

@@ -91,16 +91,10 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         "model_fields_.test_arrayfield.TestQuerying.test_icontains",
         # Field 'field' expected a number but got Value(1).
         "model_fields_.test_arrayfield.TestQuerying.test_exact_with_expression",
-        # int() argument must be a string, a bytes-like object or a real number, not 'list'
-        "model_fields_.test_arrayfield.TestQuerying.test_index_annotation",
-        # Wrong results
-        "model_fields_.test_arrayfield.TestQuerying.test_index",
-        "model_fields_.test_arrayfield.TestQuerying.test_index_chained",
-        "model_fields_.test_arrayfield.TestQuerying.test_index_nested",
-        "model_fields_.test_arrayfield.TestQuerying.test_order_by_slice",
         # $lt treats null values as zero.
         "model_fields_.test_arrayfield.TestQuerying.test_lt",
         "model_fields_.test_arrayfield.TestQuerying.test_len",
+        "model_fields_.test_arrayfield.TestQuerying.test_index_chained",
         # None is $in None
         "model_fields_.test_arrayfield.TestQuerying.test_in_as_F_object",
     }

django_mongodb/fields/array.py

@@ -183,7 +183,6 @@ def get_transform(self, name):
             except ValueError:
                 pass
             else:
-                index += 1  # postgres uses 1-indexing
                 return IndexTransformFactory(index, self.base_field)
         try:
             start, end = name.split("_")
@@ -306,10 +305,8 @@ def __init__(self, index, base_field, *args, **kwargs):
         self.base_field = base_field
 
     def as_mql(self, compiler, connection):
-        lhs, params = compiler.compile(self.lhs)
-        if not lhs.endswith("]"):
-            lhs = "(%s)" % lhs
-        return "%s[%%s]" % lhs, (*params, self.index)
+        lhs_mql = process_lhs(self, compiler, connection)
+        return {"$arrayElemAt": [lhs_mql, self.index]}
 
     @property
     def output_field(self):

tests/model_fields_/test_arrayfield.py

@@ -356,7 +356,6 @@ def test_index_nested(self):
         instance = NestedIntegerArrayModel.objects.create(field=[[1, 2], [3, 4]])
         self.assertSequenceEqual(NestedIntegerArrayModel.objects.filter(field__0__0=1), [instance])
 
-    @unittest.expectedFailure
     def test_index_used_on_nested_data(self):
         instance = NestedIntegerArrayModel.objects.create(field=[[1, 2], [3, 4]])
         self.assertSequenceEqual(
@@ -388,7 +387,7 @@ def test_slice(self):
             NullableIntegerArrayModel.objects.filter(field__0_2=[2, 3]), self.objs[2:3]
         )
 
-    def test_order_by_slice(self):
+    def test_order_by_index(self):
         more_objs = (
             NullableIntegerArrayModel.objects.create(field=[1, 637]),
             NullableIntegerArrayModel.objects.create(field=[2, 1]),
@@ -398,19 +397,18 @@ def test_order_by_slice(self):
         self.assertSequenceEqual(
             NullableIntegerArrayModel.objects.order_by("field__1"),
             [
+                self.objs[0],
+                self.objs[1],
+                self.objs[4],
                 more_objs[2],
                 more_objs[1],
                 more_objs[3],
                 self.objs[2],
                 self.objs[3],
                 more_objs[0],
-                self.objs[4],
-                self.objs[1],
-                self.objs[0],
             ],
         )
 
-    @unittest.expectedFailure
     def test_slice_nested(self):
         instance = NestedIntegerArrayModel.objects.create(field=[[1, 2], [3, 4]])
         self.assertSequenceEqual(