Adds all_pks() method and test.

aredis_om/model/model.py

@@ -1483,6 +1483,22 @@ class JsonModel(RedisModel, abc.ABC):
         await db.execute_command("JSON.SET", self.key(), ".", self.json())
         return self
 
+    @classmethod
+    async def all_pks(cls):  # type: ignore
+        key_prefix = cls.make_key(cls._meta.primary_key_pattern.format(pk=""))
+        # TODO: We assume the key ends with the default separator, ":" -- when
+        #  we make the separator configurable, we need to update this as well.
+        #  ... And probably lots of other places ...
+        #
+        # TODO: Also, we need to decide how we want to handle the lack of
+        #  decode_responses=True...
+        return (
+            key.split(":")[-1]
+            if isinstance(key, str)
+            else key.decode(cls.Meta.encoding).split(":")[-1]
+            async for key in cls.db().scan_iter(f"{key_prefix}*", _type="ReJSON-RL")
+        )
+
     async def update(self, **field_values):
         validate_model_fields(self.__class__, field_values)
         for field, value in field_values.items():