Cache resolved classes for fields, so that there's no new data classes generated while deserializing.

betterproto/__init__.py

@@ -452,25 +452,49 @@ class ProtoClassMetadata:
         self.oneof_group_by_field = by_field
         self.oneof_field_by_group = by_group
 
+    def init_default_gen(self):
+        default_gen = {}
+
+        for field in dataclasses.fields(self.cls):
+            meta = FieldMetadata.get(field)
+            default_gen[field.name] = self.cls._get_field_default_gen(field, meta)
+
+        self.default_gen = default_gen
+
+    def init_cls_by_field(self):
+        field_cls = {}
+
+        for field in dataclasses.fields(self.cls):
+            meta = FieldMetadata.get(field)
+            if meta.proto_type == TYPE_MAP:
+                assert meta.map_types
+                kt = self.cls._cls_for(field, index=0)
+                vt = self.cls._cls_for(field, index=1)
+                Entry = dataclasses.make_dataclass(
+                    "Entry",
+                    [
+                        ("key", kt, dataclass_field(1, meta.map_types[0])),
+                        ("value", vt, dataclass_field(2, meta.map_types[1])),
+                    ],
+                    bases=(Message,),
+                )
+                make_protoclass(Entry)
+                field_cls[field.name] = Entry
+                field_cls[field.name + ".value"] = vt
+            else:
+                field_cls[field.name] = self.cls._cls_for(field)
+
+        self.cls_by_field = field_cls
+
     def __getattr__(self, item):
         # Lazy init because forward reference classes may not be available at the beginning.
         if item == 'default_gen':
-            defaults = {}
+            self.init_default_gen()
-            for field in dataclasses.fields(self.cls):
+            return self.default_gen
-                meta = FieldMetadata.get(field)
-                defaults[field.name] = self.cls._get_field_default_gen(field, meta)
-
-            self.default_gen = defaults  # __getattr__ won't be called next time
-            return defaults
 
         if item == 'cls_by_field':
-            field_cls = {}
+            self.init_cls_by_field()
-            for field in dataclasses.fields(self.cls):
+            return self.cls_by_field
-                meta = FieldMetadata.get(field)
-                field_cls[field.name] = self.cls._type_hint(field.name)
-
-            self.cls_by_field = field_cls  # __getattr__ won't be called next time
-            return field_cls
 
 
 def make_protoclass(cls):
@@ -619,12 +643,13 @@ class Message(ABC):
         type_hints = get_type_hints(cls, vars(module))
         return type_hints[field_name]
 
-    def _cls_for(self, field: dataclasses.Field, index: int = 0) -> Type:
+    @classmethod
+    def _cls_for(cls, field: dataclasses.Field, index: int = 0) -> Type:
         """Get the message class for a field from the type hints."""
-        cls = self._betterproto.cls_by_field[field.name]
+        field_cls = cls._type_hint(field.name)
-        if hasattr(cls, "__args__") and index >= 0:
+        if hasattr(field_cls, "__args__") and index >= 0:
-            cls = cls.__args__[index]
+            field_cls = field_cls.__args__[index]
-        return cls
+        return field_cls
 
     def _get_field_default(self, field: dataclasses.Field, meta: FieldMetadata) -> Any:
         return self._betterproto.default_gen[field.name]()
@@ -680,7 +705,7 @@ class Message(ABC):
             if meta.proto_type == TYPE_STRING:
                 value = value.decode("utf-8")
             elif meta.proto_type == TYPE_MESSAGE:
-                cls = self._cls_for(field)
+                cls = self._betterproto.cls_by_field[field.name]
 
                 if cls == datetime:
                     value = _Timestamp().parse(value).to_datetime()
@@ -694,21 +719,7 @@ class Message(ABC):
                     value = cls().parse(value)
                     value._serialized_on_wire = True
             elif meta.proto_type == TYPE_MAP:
-                # TODO: This is slow, use a cache to make it faster since each
+                value = self._betterproto.cls_by_field[field.name]().parse(value)
-                #       key/value pair will recreate the class.
-                assert meta.map_types
-                kt = self._cls_for(field, index=0)
-                vt = self._cls_for(field, index=1)
-                Entry = dataclasses.make_dataclass(
-                    "Entry",
-                    [
-                        ("key", kt, dataclass_field(1, meta.map_types[0])),
-                        ("value", vt, dataclass_field(2, meta.map_types[1])),
-                    ],
-                    bases=(Message,),
-                )
-                make_protoclass(Entry)
-                value = Entry().parse(value)
 
         return value
 
@@ -823,7 +834,7 @@ class Message(ABC):
                     else:
                         output[cased_name] = b64encode(v).decode("utf8")
                 elif meta.proto_type == TYPE_ENUM:
-                    enum_values = list(self._cls_for(field))  # type: ignore
+                    enum_values = list(self._betterproto.cls_by_field[field.name])  # type: ignore
                     if isinstance(v, list):
                         output[cased_name] = [enum_values[e].name for e in v]
                     else:
@@ -849,7 +860,7 @@ class Message(ABC):
                     if meta.proto_type == "message":
                         v = getattr(self, field.name)
                         if isinstance(v, list):
-                            cls = self._cls_for(field)
+                            cls = self._betterproto.cls_by_field[field.name]
                             for i in range(len(value[key])):
                                 v.append(cls().from_dict(value[key][i]))
                         elif isinstance(v, datetime):
@@ -866,7 +877,7 @@ class Message(ABC):
                             v.from_dict(value[key])
                     elif meta.map_types and meta.map_types[1] == TYPE_MESSAGE:
                         v = getattr(self, field.name)
-                        cls = self._cls_for(field, index=1)
+                        cls = self._betterproto.cls_by_field[field.name + ".value"]
                         for k in value[key]:
                             v[k] = cls().from_dict(value[key][k])
                     else:
@@ -882,7 +893,7 @@ class Message(ABC):
                             else:
                                 v = b64decode(value[key])
                         elif meta.proto_type == TYPE_ENUM:
-                            enum_cls = self._cls_for(field)
+                            enum_cls = self._betterproto.cls_by_field[field.name]
                             if isinstance(v, list):
                                 v = [enum_cls.from_string(e) for e in v]
                             elif isinstance(v, str):