Check whether property value has changed after transform (#7432)

* Check whether property value has changed after transform

* Add test

panel/reactive.py

@@ -1582,16 +1582,32 @@ def _process_param_change(self, params):
     def _set_on_model(self, msg: Mapping[str, Any], root: Model, model: Model) -> None:
         if not msg:
             return
-        old = self._changing.get(root.ref['id'], [])
-        self._changing[root.ref['id']] = [
-            attr for attr, value in msg.items()
-            if not model.lookup(attr).property.matches(getattr(model, attr), value)
-        ]
+        prev_changing = self._changing.get(root.ref['id'], [])
+        changing = []
+        transformed = {}
+        for attr, value in msg.items():
+            prop = model.lookup(attr).property
+            old = getattr(model, attr)
+            try:
+                matches = bool(prop.matches(old, value))
+            except Exception:
+                for tp, converter in prop.alternatives:
+                    if tp.is_valid(value):
+                        value = converter(value)
+                        break
+                try:
+                    matches = bool(prop.matches(old, value))
+                except Exception:
+                    matches = False
+            if not matches:
+                transformed[attr] = value
+                changing.append(attr)
+        self._changing[root.ref['id']] = changing
         try:
-            model.update(**msg)
+            model.update(**transformed)
         finally:
             if old:
-                self._changing[root.ref['id']] = old
+                self._changing[root.ref['id']] = prev_changing
             else:
                 del self._changing[root.ref['id']]
 

panel/tests/test_custom.py

@@ -1,3 +1,5 @@
+import numpy as np
+import pandas as pd
 import param
 
 from panel.custom import PyComponent, ReactiveESM
@@ -44,6 +46,25 @@ def test_py_component_cleanup(document, comm):
     assert not spy._view__._models
 
 
+class ESMDataFrame(ReactiveESM):
+
+    df = param.DataFrame()
+
+
+def test_reactive_esm_sync_dataframe(document, comm):
+    esm_df = ESMDataFrame()
+
+    model = esm_df.get_root(document, comm)
+
+    esm_df.df = pd.DataFrame({"1": [2]})
+
+    assert isinstance(model.data.df, dict)
+    assert len(model.data.df) == 2
+    expected = {"index": np.array([0]), "1": np.array([2])}
+    for col, values in model.data.df.items():
+        np.testing.assert_array_equal(values, expected.get(col))
+
+
 class ESMWithChildren(ReactiveESM):
 
     child = param.ClassSelector(class_=Viewable)