fix: backward pagination (#1346)

Co-authored-by: Thomas Leonard <thomas@loftorbital.com> Co-authored-by: Laurent <laurent.riviere.pro@gmail.com>

Author: 3 people

graphene_django/fields.py

@@ -152,22 +152,24 @@ def resolve_connection(cls, connection, args, iterable, max_limit=None):
  array_length = iterable.count()
  else:
  array_length = len(iterable)
- array_slice_length = (
- min(max_limit, array_length) if max_limit is not None else array_length
- )
 
- # If after is higher than list_length, connection_from_list_slice
+ # If after is higher than array_length, connection_from_array_slice
  # would try to do a negative slicing which makes django throw an
  # AssertionError
  slice_start = min(
- get_offset_with_default(args.get("after"), -1) + 1, array_length
+ get_offset_with_default(args.get("after"), -1) + 1,
+ array_length,
  )
-
- if max_limit is not None and args.get("first", None) is None:
- if args.get("last", None) is not None:
- slice_start = max(array_length - args["last"], 0)
- else:
- args["first"] = max_limit
+ array_slice_length = array_length - slice_start
+
+ # Impose the maximum limit via the `first` field if neither first or last are already provided
+ # (note that if any of them is provided they must be under max_limit otherwise an error is raised).
+ if (
+ max_limit is not None
+ and args.get("first", None) is None
+ and args.get("last", None) is None
+ ):
+ args["first"] = max_limit
 
  connection = connection_from_array_slice(
  iterable[slice_start:],

graphene_django/tests/test_query.py

@@ -1243,6 +1243,7 @@ class Query(graphene.ObjectType):
  }
 
 
+@pytest.mark.parametrize("max_limit", [100, 4])
 class TestBackwardPagination:
  def setup_schema(self, graphene_settings, max_limit):
  graphene_settings.RELAY_CONNECTION_MAX_LIMIT = max_limit
@@ -1261,8 +1262,8 @@ class Query(graphene.ObjectType):
  schema = graphene.Schema(query=Query)
  return schema
 
- def do_queries(self, schema):
- # Simply last 3
+ def test_query_last(self, graphene_settings, max_limit):
+ schema = self.setup_schema(graphene_settings, max_limit=max_limit)
  query_last = """
  query {
  allReporters(last: 3) {
@@ -1282,7 +1283,8 @@ def do_queries(self, schema):
  e["node"]["firstName"] for e in result.data["allReporters"]["edges"]
  ] == ["First 3", "First 4", "First 5"]
 
- # Use a combination of first and last
+ def test_query_first_and_last(self, graphene_settings, max_limit):
+ schema = self.setup_schema(graphene_settings, max_limit=max_limit)
  query_first_and_last = """
  query {
  allReporters(first: 4, last: 3) {
@@ -1302,7 +1304,8 @@ def do_queries(self, schema):
  e["node"]["firstName"] for e in result.data["allReporters"]["edges"]
  ] == ["First 1", "First 2", "First 3"]
 
- # Use a combination of first and last and after
+ def test_query_first_last_and_after(self, graphene_settings, max_limit):
+ schema = self.setup_schema(graphene_settings, max_limit=max_limit)
  query_first_last_and_after = """
  query queryAfter($after: String) {
  allReporters(first: 4, last: 3, after: $after) {
@@ -1317,28 +1320,44 @@ def do_queries(self, schema):
 
  after = base64.b64encode(b"arrayconnection:0").decode()
  result = schema.execute(
- query_first_last_and_after, variable_values=dict(after=after)
+ query_first_last_and_after,
+ variable_values=dict(after=after),
  )
  assert not result.errors
  assert len(result.data["allReporters"]["edges"]) == 3
  assert [
  e["node"]["firstName"] for e in result.data["allReporters"]["edges"]
  ] == ["First 2", "First 3", "First 4"]
 
- def test_should_query(self, graphene_settings):
- """
- Backward pagination should work as expected
+ def test_query_last_and_before(self, graphene_settings, max_limit):
+ schema = self.setup_schema(graphene_settings, max_limit=max_limit)
+ query_first_last_and_after = """
+ query queryAfter($before: String) {
+ allReporters(last: 1, before: $before) {
+ edges {
+ node {
+ firstName
+ }
+ }
+ }
+ }
  """
- schema = self.setup_schema(graphene_settings, max_limit=100)
- self.do_queries(schema)
 
- def test_should_query_with_low_max_limit(self, graphene_settings):
- """
- When doing backward pagination (using last) in combination with a max limit higher than the number of objects
- we should really retrieve the last ones.
- """
- schema = self.setup_schema(graphene_settings, max_limit=4)
- self.do_queries(schema)
+ result = schema.execute(
+ query_first_last_and_after,
+ )
+ assert not result.errors
+ assert len(result.data["allReporters"]["edges"]) == 1
+ assert result.data["allReporters"]["edges"][0]["node"]["firstName"] == "First 5"
+
+ before = base64.b64encode(b"arrayconnection:5").decode()
+ result = schema.execute(
+ query_first_last_and_after,
+ variable_values=dict(before=before),
+ )
+ assert not result.errors
+ assert len(result.data["allReporters"]["edges"]) == 1
+ assert result.data["allReporters"]["edges"][0]["node"]["firstName"] == "First 4"
 
 
 def test_should_preserve_prefetch_related(django_assert_num_queries):