skip building new children when embedding (#6881)

panel/tests/widgets/test_tables.py

@@ -336,7 +336,7 @@ def test_tabulator_expanded_content_pagination(document, comm):
     assert len(model.children) == 0
 
 
-def test_tabulator_expanded_content_embed(document, comm):
+def test_tabulator_content_embed(document, comm):
     df = makeMixedDataFrame()
 
     table = Tabulator(df, embed_content=True, row_content=lambda r: r.A)
@@ -358,6 +358,34 @@ def test_tabulator_expanded_content_embed(document, comm):
         assert row.text  == f"<pre>{r.A+1}</pre>"
 
 
+def test_tabulator_content_embed_and_expand(document, comm):
+    # https://github.com/holoviz/panel/issues/6200
+    df = makeMixedDataFrame()
+
+    calls = []
+    def row_content(row):
+        calls.append(row)
+        return row.A
+
+    table = Tabulator(df, embed_content=True, row_content=row_content)
+
+    model = table.get_root(document, comm)
+
+    assert len(calls) == len(df)
+
+    assert len(model.children) == len(df)
+
+    for i, r in df.iterrows():
+        assert i in model.children
+        row = model.children[i]
+        assert row.text  == f"<pre>{r.A}</pre>"
+
+    # Expanding a row should not call row_content again in this context.
+    table.expanded = [1]
+
+    assert len(calls) == len(df)
+
+
 def test_tabulator_selected_and_filtered_dataframe(document, comm):
     df = makeMixedDataFrame()
     table = Tabulator(df, selection=list(range(len(df))))

panel/widgets/tables.py

@@ -1484,18 +1484,22 @@ def _indexes_changed(self, old, new):
     def _update_children(self, *events):
         cleanup, reuse = set(), set()
         page_events = ('page', 'page_size', 'pagination')
+        old_panels = self._child_panels
         for event in events:
             if event.name == 'expanded' and len(events) == 1:
-                cleanup = set(event.old) - set(event.new)
-                reuse = set(event.old) & set(event.new)
+                if self.embed_content:
+                    cleanup = set()
+                    reuse = set(old_panels)
+                else:
+                    cleanup = set(event.old) - set(event.new)
+                    reuse = set(event.old) & set(event.new)
             elif (
               (event.name == 'value' and self._indexes_changed(event.old, event.new)) or
               (event.name in page_events and not self._updating) or
               (self.pagination == 'remote' and event.name == 'sorters')
             ):
                 self.expanded = []
                 return
-        old_panels = self._child_panels
         self._child_panels = child_panels = self._get_children(
             {i: old_panels[i] for i in reuse}
         )