proper computed var change detection

reflex/state.py

@@ -370,6 +370,9 @@ class BaseState(Base, ABC, extra=pydantic.Extra.allow):
     # A special event handler for setting base vars.
     setvar: ClassVar[EventHandler]
 
+    # Track if computed vars have changed since last serialization
+    _changed_computed_vars: Set[str] = set()
+
     def __init__(
         self,
         parent_state: BaseState | None = None,
@@ -1825,14 +1828,11 @@ class BaseState(Base, ABC, extra=pydantic.Extra.allow):
             calc_vars, dirty_vars = dirty_vars, set()
             for cvar in self._dirty_computed_vars(from_vars=calc_vars):
                 actual_var = self.computed_vars.get(cvar)
-                if actual_var is not None:
-                    if actual_var.has_changed(instance=self):
-                        actual_var.mark_dirty(instance=self)
-                    else:
-                        # var has not changed, do not mark as dirty
-                        continue
-                self.dirty_vars.add(cvar)
-                dirty_vars.add(cvar)
+                assert actual_var is not None
+                if actual_var.has_changed(instance=self):
+                    actual_var.mark_dirty(instance=self)
+                    self.dirty_vars.add(cvar)
+                    dirty_vars.add(cvar)
 
     def _expired_computed_vars(self) -> set[str]:
         """Determine ComputedVars that need to be recalculated based on the expiration time.
@@ -2112,6 +2112,7 @@ class BaseState(Base, ABC, extra=pydantic.Extra.allow):
         state["__dict__"]["parent_state"] = None
         state["__dict__"]["substates"] = {}
         state["__dict__"].pop("_was_touched", None)
+        state["__dict__"].pop("_changed_computed_vars", None)
         # Remove all inherited vars.
         for inherited_var_name in self.inherited_vars:
             state["__dict__"].pop(inherited_var_name, None)

reflex/utils/types.py

@@ -122,6 +122,7 @@ RESERVED_BACKEND_VAR_NAMES = {
     "_abc_impl",
     "_backend_vars",
     "_was_touched",
+    "_changed_computed_vars",
 }
 
 if sys.version_info >= (3, 11):

reflex/vars/base.py

@@ -2027,8 +2027,16 @@ class ComputedVar(Var[RETURN_TYPE]):
         else:
             # handle caching
             if not hasattr(instance, self._cache_attr) or self.needs_update(instance):
+                # Get the new value.
+                new_value = self.fget(instance)
+                # Get the current cached value.
+                cached_value = getattr(instance, self._cache_attr, None)
+                # Check if the new value is different from the cached value.
+                if new_value == cached_value:
+                    return new_value
+                instance._changed_computed_vars.add(self._js_expr)
                 # Set cache attr on state instance.
-                setattr(instance, self._cache_attr, self.fget(instance))
+                setattr(instance, self._cache_attr, new_value)
                 # Ensure the computed var gets serialized to redis.
                 instance._was_touched = True
                 # Set the last updated timestamp on the state instance.
@@ -2176,9 +2184,19 @@ class ComputedVar(Var[RETURN_TYPE]):
         Returns:
             True if the value has changed, False otherwise.
         """
-        cached_value = getattr(instance, self._cache_attr, None)
+        if not self._cache:
+            return True
+        if self._js_expr in instance._changed_computed_vars:
+            return True
+        if not hasattr(instance, self._cache_attr):
+            return True
+        cached_value = getattr(instance, self._cache_attr)
         new_value = self.fget(instance)
-        return cached_value != new_value
+        has_changed = cached_value != new_value
+        if has_changed:
+            instance._changed_computed_vars.add(self._js_expr)
+            setattr(instance, self._cache_attr, new_value)
+        return has_changed
 
     def _determine_var_type(self) -> Type:
         """Get the type of the var.