BUGFIX: Do not check hashes in store method if node is already stored

In this case the _df attribute does not necessarily exist as it is
created from a database query and not via __init__

aiida_dataframe/data/dataframe.py

@@ -130,8 +130,12 @@ def store(self, *args, **kwargs) -> PandasFrameData:
         on the dataframe e.g. `df["A"] = new_value`
         This is only done if the hashes of the DATA does not match up
         """
-        current_hash = self._hash_dataframe(self._df)
-        if current_hash != self.get_attribute("_pandas_data_hash"):
-            self._update_dataframe(self._df)
+        if not self.is_stored:
+            # Check if the dataframe directly attached to the node
+            # has been mutated in place before storing
+            # If so the underlying file is updated
+            current_hash = self._hash_dataframe(self._df)
+            if current_hash != self.get_attribute("_pandas_data_hash"):
+                self._update_dataframe(self._df)
 
         return super().store(*args, **kwargs)

tests/test_data.py

@@ -494,3 +494,40 @@ def test_non_default_filename(entry_point):
     assert loaded is not node
     assert loaded.list_object_names() == ["non_default.h5"]
     assert_frame_equal(loaded.df, df)
+
+
+@pytest.mark.parametrize(
+    "entry_point",
+    ("dataframe.frame",),
+)
+def test_modification_store_already_stored(entry_point):
+    """
+    Test that callign store on an already stroed node does nothing
+    (Including crashes)
+    """
+
+    PandasFrameData = DataFactory(entry_point)
+
+    # Example from pandas Docs
+    df = pd.DataFrame(
+        {
+            "A": 1.0,
+            "B": pd.Timestamp("20130102"),
+            "C": pd.Series(1, index=list(range(4)), dtype="float32"),
+            "D": np.array([3] * 4, dtype="int32"),
+            "E": pd.Categorical(["test", "train", "test", "train"]),
+            "F": "foo",
+        }
+    )
+
+    node = PandasFrameData(df)
+    node.store()
+    assert node.is_stored
+
+    loaded = load_node(node.pk)
+    assert loaded is not node
+    assert_frame_equal(loaded.df, df)
+
+    loaded_store = loaded.store()
+    assert loaded_store is loaded
+    assert_frame_equal(loaded_store.df, df)