Allow to change a fragment name after initialization

Author: leszekhanusz

gql/dsl.py

@@ -753,10 +753,23 @@ def __init__(
 
         self.name = name
         self._type = None
-        self.ast_field = FragmentSpreadNode()
-        self.ast_field.name = NameNode(value=self.name)
+
         log.debug(f"Creating {self!r}")
 
+    @property  # type: ignore
+    def ast_field(self) -> FragmentSpreadNode:  # type: ignore
+        """ast_field property will generate a FragmentSpreadNode with the
+        provided name.
+
+        Note: We need to ignore the type because of
+        `issue #4125 of mypy <https://github.com/python/mypy/issues/4125>`_.
+        """
+
+        spread_node = FragmentSpreadNode()
+        spread_node.name = NameNode(value=self.name)
+
+        return spread_node
+
     def select(
         self, *fields: "DSLSelectable", **fields_with_alias: "DSLSelectableWithAlias"
     ) -> "DSLFragment":

tests/starwars/test_dsl.py

@@ -499,6 +499,17 @@ def test_fragment_without_type_condition_error(ds):
         dsl_gql(name_and_appearances)
 
 
+def test_fragment_with_name_changed(ds):
+
+    fragment = DSLFragment("ABC")
+
+    assert str(fragment) == "...ABC"
+
+    fragment.name = "DEF"
+
+    assert str(fragment) == "...DEF"
+
+
 def test_dsl_nested_query_with_fragment(ds):
     query = """fragment NameAndAppearances on Character {
   name