JP-3721: Simplify ModelContainer (spacetelescope#8831)

Author: emolter

changes/8831.datamodels.rst

@@ -0,0 +1 @@
+Remove memory-saving options from ModelContainer

docs/jwst/stpipe/devel_io_design.rst

@@ -163,15 +163,47 @@ Many of the JWST calibration steps and pipelines expect an
 :ref:`Association <associations>` file as input. When opened with
 :meth:`~jwst.stpipe.step.Step.open_model`, a
 :class:`~jwst.datamodels.ModelContainer` is returned. `ModelContainer`
-is, among other features, a list-like object where each element is the
-`DataModel` of each member of the association. The `meta.asn_table` is
+is a list-like object where each element is the
+`DataModel` of each member of the association. The `asn_table` attribute is
 populated with the association data structure, allowing direct access
 to the association itself.  The association file, as well as the files
 listed in the association file, must be in the input directory.
 
 To read in a list of files, or an association file, as an association,
 use the `load_as_level2_asn` or `load_as_level3_asn` methods.
 
+ModelContainer vs ModelLibrary
+``````````````````````````````
+
+Some steps in the pipeline, namely any steps involved in the Stage 3 Imaging pipeline,
+rely on the :class:`~jwst.datamodels.ModelLibrary` class instead of the
+:class:`~jwst.datamodels.ModelContainer` class to process association-type data.
+The `ModelLibrary` class is purpose-built for enabling memory-saving options in the
+image3 pipeline and is only recommended when working with large associations.
+Additional documentation on the `ModelLibrary` class can be found in the
+`stpipe ModelLibrary documentation <https://stpipe.readthedocs.io/en/latest/model_library.html>`_.
+
+ModelContainer Changes in JWST 1.17
+```````````````````````````````````
+
+In JWST 1.17, the `ModelContainer` class was de-scoped in light of the introduction of the
+`ModelLibrary` class in JWST 1.16. The `ModelContainer` class is still the recommended class
+for handling association-type data, but it is no longer a subclass of `JWSTDataModel`. The
+following changes in behavior are noteworthy:
+
+* The `ModelContainer` class no longer has a `meta` attribute. The association data is now
+  stored in the top-level `asn_table` attribute, along with several other association-relevant
+  attributes including `asn_table_name`, `asn_pool_name`, `asn_exptypes`, `asn_n_members`, 
+  `asn_file_path`. Note that `asn_table` is now a dictionary, not an `ObjectNode`.
+* All infrastructure that attempted memory savings in the `ModelContainer` class has been removed.
+  Use the `ModelLibrary` class if memory-saving options are needed.
+* A `ModelContainer` object can no longer hold a list of `ModelContainer` objects.
+* The `ModelContainer` class is still list-like, and can be indexed and sliced like a list.
+* The `ModelContainer` class is still the default class returned by stdatamodels `open()`
+  for association-type input data, e.g. a .json file or dict.
+* The `ModelContainer` class can still be used as a context manager, such that `with open(asn_file.json)`
+  still works.
+
 Input Source
 ------------
 

jwst/badpix_selfcal/badpix_selfcal_step.py

@@ -35,8 +35,7 @@ class BadpixSelfcalStep(Step):
     """
 
     def save_model(self, model, *args, **kwargs):
-        """Override save_model to suppress index 0 when save_model is True
-        """
+        """Override save_model to suppress index 0 when save_model is True"""
         kwargs["idx"] = None
         return Step.save_model(self, model, *args, **kwargs)
 

jwst/cube_build/data_types.py

@@ -89,7 +89,7 @@ def __init__(self, input, single, output_file, output_dir):
             self.output_name = 'Temp'
             self.input_models = input_models
             if not single:  # find the name of the output file from the association
-                self.output_name = input_models.meta.asn_table.products[0].name
+                self.output_name = input_models.asn_table["products"][0]["name"]
         else:
             # close files opened above
             self.close()