RCAL-723 Fix model.meta.filename when saving model

CHANGES.rst

@@ -4,6 +4,8 @@
 - Allow assignment to or creation of node attributes using dot notation of object instances
   with validation. [#284]
 
+- Bugfix for ``model.meta.filename`` not matching the filename of the file on disk. [#295]
+
 0.18.0 (2023-11-06)
 ===================
 

src/roman_datamodels/datamodels/_core.py

@@ -11,10 +11,9 @@
 import copy
 import datetime
 import functools
-import os
-import os.path
 import sys
-from pathlib import PurePath
+from contextlib import contextmanager
+from pathlib import Path, PurePath
 
 import asdf
 import numpy as np
@@ -48,6 +47,26 @@ def wrapper(self, *args, **kwargs):
     return wrapper
 
 
+@contextmanager
+def _temporary_update_filename(datamodel, filename):
+    """
+    Context manager to temporarily update the filename of a datamodel so that it
+    can be saved with that new file name without changing the current model's filename
+    """
+    from roman_datamodels.stnode import Filename
+
+    if "meta" in datamodel._instance and "filename" in datamodel._instance.meta:
+        old_filename = datamodel._instance.meta.filename
+        datamodel._instance.meta.filename = Filename(filename)
+
+        yield
+        datamodel._instance.meta.filename = old_filename
+        return
+
+    yield
+    return
+
+
 class DataModel(abc.ABC):
     """Base class for all top level datamodels"""
 
@@ -181,17 +200,9 @@ def clone(target, source, deepcopy=False, memo=None):
         target._ctx = target
 
     def save(self, path, dir_path=None, *args, **kwargs):
-        if callable(path):
-            path_head, path_tail = os.path.split(path(self.meta.filename))
-        else:
-            path_head, path_tail = os.path.split(path)
-        base, ext = os.path.splitext(path_tail)
-        if isinstance(ext, bytes):
-            ext = ext.decode(sys.getfilesystemencoding())
-
-        if dir_path:
-            path_head = dir_path
-        output_path = os.path.join(path_head, path_tail)
+        path = Path(path(self.meta.filename) if callable(path) else path)
+        output_path = Path(dir_path) / path.name if dir_path else path
+        ext = path.suffix.decode(sys.getfilesystemencoding()) if isinstance(path.suffix, bytes) else path.suffix
 
         # TODO: Support gzip-compressed fits
         if ext == ".asdf":
@@ -206,10 +217,10 @@ def open_asdf(self, init=None, **kwargs):
             return asdf.open(init, **kwargs) if isinstance(init, str) else asdf.AsdfFile(init, **kwargs)
 
     def to_asdf(self, init, *args, **kwargs):
-        with validate.nuke_validation():
-            asdffile = self.open_asdf(**kwargs)
-            asdffile.tree = {"roman": self._instance}
-            asdffile.write_to(init, *args, **kwargs)
+        with validate.nuke_validation(), _temporary_update_filename(self, Path(init).name):
+            asdf_file = self.open_asdf(**kwargs)
+            asdf_file.tree = {"roman": self._instance}
+            asdf_file.write_to(init, *args, **kwargs)
 
     def get_primary_array_name(self):
         """

tests/test_models.py

@@ -804,3 +804,15 @@ def test_datamodel_construct_like_from_like(model):
     new_mdl = model(mdl)
     assert new_mdl is mdl
     assert new_mdl._iscopy == "foo"  # Verify that the constructor didn't override stuff
+
+
+def test_datamodel_save_filename(tmp_path):
+    filename = tmp_path / "fancy_filename.asdf"
+    ramp = utils.mk_datamodel(datamodels.RampModel, shape=(2, 8, 8))
+    assert ramp.meta.filename != filename.name
+
+    ramp.save(filename)
+    assert ramp.meta.filename != filename.name
+
+    with datamodels.open(filename) as new_ramp:
+        assert new_ramp.meta.filename == filename.name