Optimize columns loading: lazy create row locator

src/gino/crud.py

@@ -87,13 +87,18 @@ def __init__(self, instance: "CRUDModel"):
         self._props = {}
         self._literal = True
         self._locator = None
-        if instance.__table__ is not None:
+
+    @property
+    def locator(self):
+        if self._locator is None and self._instance.__table__ is not None:
             try:
-                self._locator = instance.lookup()
+                self._locator = self._instance.lookup()
             except LookupError:
                 # apply() will fail anyway, but still allow update()
                 pass
 
+        return self._locator
+
     def _set(self, key, value):
         self._values[key] = value
 
@@ -116,7 +121,7 @@ async def apply(self, bind=None, timeout=DEFAULT):
         :return: ``self`` for chaining calls.
 
         """
-        if self._locator is None:
+        if self.locator is None:
             raise TypeError(
                 "Model {} has no table, primary key or custom lookup()".format(
                     self._instance.__class__.__name__
@@ -167,7 +172,7 @@ async def apply(self, bind=None, timeout=DEFAULT):
         clause = (
             type(self._instance)
             .update.where(
-                self._locator,
+                self.locator,
             )
             .values(
                 **self._instance._get_sa_values(values),
@@ -435,7 +440,8 @@ class CRUDModel(Model):
     def __init__(self, **values):
         super().__init__()
         self.__profile__ = None
-        self._update_request_cls(self).update(**values)
+        if values:
+            self._update_request_cls(self).update(**values)
 
     @classmethod
     def _init_table(cls, sub_cls):