Move component handling out of dataset manager.

findDataset and getDatasetType are no the only registry methods that
support components; removing support from those would cause a lot of
inconvenience downstream, and the complexity cost in Registry for
keeping it there is quite low. But we want to get it out of the manager
classes to get rid of that unpleasant copy.copy on the storage object,
and to keep component support from accidentally spreading to other
places where we don't want to maintain it.

At the same time, I've changed the exception raised for missing dataset
types in the manager to be MissingDatasetTypeError for consistency with
the query methods, but adding KeyError as a base class of that
exception to maintain backwards compatibility.

python/lsst/daf/butler/registries/sql.py

@@ -418,7 +418,12 @@ def removeDatasetType(self, name: str) -> None:
 
     def getDatasetType(self, name: str) -> DatasetType:
         # Docstring inherited from lsst.daf.butler.registry.Registry
-        return self._managers.datasets[name].datasetType
+        parent_name, component = DatasetType.splitDatasetTypeName(name)
+        storage = self._managers.datasets[parent_name]
+        if component is None:
+            return storage.datasetType
+        else:
+            return storage.datasetType.makeComponentDatasetType(component)
 
     def supportsIdGenerationMode(self, mode: DatasetIdGenEnum) -> bool:
         # Docstring inherited from lsst.daf.butler.registry.Registry
@@ -435,9 +440,14 @@ def findDataset(
     ) -> Optional[DatasetRef]:
         # Docstring inherited from lsst.daf.butler.registry.Registry
         if isinstance(datasetType, DatasetType):
-            storage = self._managers.datasets[datasetType.name]
+            parent_name, component = datasetType.nameAndComponent()
+            storage = self._managers.datasets[parent_name]
         else:
-            storage = self._managers.datasets[datasetType]
+            parent_name, component = DatasetType.splitDatasetTypeName(datasetType)
+            storage = self._managers.datasets[parent_name]
+            datasetType = storage.datasetType
+            if component is not None:
+                datasetType.makeComponentDatasetType(component)
         dataId = DataCoordinate.standardize(
             dataId,
             graph=storage.datasetType.dimensions,
@@ -460,6 +470,8 @@ def findDataset(
                 continue
             result = storage.find(collectionRecord, dataId, timespan=timespan)
             if result is not None:
+                if component is not None:
+                    return result.makeComponentRef(component)
                 return result
 
         return None

python/lsst/daf/butler/registry/_exceptions.py

@@ -67,7 +67,7 @@ class DatasetTypeError(RegistryError):
     """Exception raised for problems with dataset types."""
 
 
-class MissingDatasetTypeError(DatasetTypeError):
+class MissingDatasetTypeError(DatasetTypeError, KeyError):
     """Exception raised when a dataset type does not exist."""
 
 

python/lsst/daf/butler/registry/_registry.py

@@ -639,8 +639,13 @@ def getDatasetType(self, name: str) -> DatasetType:
 
         Raises
         ------
-        KeyError
-            Requested named DatasetType could not be found in registry.
+        MissingDatasetTypeError
+            Raised if the requested dataset type has not been registered.
+
+        Notes
+        -----
+        This method handles component dataset types automatically, though most
+        other registry operations do not.
         """
         raise NotImplementedError()
 
@@ -712,7 +717,7 @@ def findDataset(
             ``self.defaults.collections`` is `None`.
         LookupError
             Raised if one or more data ID keys are missing.
-        KeyError
+        MissingDatasetTypeError
             Raised if the dataset type does not exist.
         MissingCollectionError
             Raised if any of ``collections`` does not exist in the registry.
@@ -728,6 +733,9 @@ def findDataset(
         reported consistently, regardless of the reason, and that adding
         additional collections that do not contain a match to the search path
         never changes the behavior.
+
+        This method handles component dataset types automatically, though most
+        other registry operations do not.
         """
         raise NotImplementedError()
 

python/lsst/daf/butler/registry/datasets/byDimensions/_manager.py

@@ -5,7 +5,6 @@
     "ByDimensionsDatasetRecordStorageManagerUUID",
 )
 
-import copy
 import logging
 import warnings
 from collections import defaultdict
@@ -254,14 +253,7 @@ def remove(self, name: str) -> None:
 
     def find(self, name: str) -> DatasetRecordStorage | None:
         # Docstring inherited from DatasetRecordStorageManager.
-        compositeName, componentName = DatasetType.splitDatasetTypeName(name)
-        storage = self._byName.get(compositeName)
-        if storage is not None and componentName is not None:
-            componentStorage = copy.copy(storage)
-            componentStorage.datasetType = storage.datasetType.makeComponentDatasetType(componentName)
-            return componentStorage
-        else:
-            return storage
+        return self._byName.get(name)
 
     def register(self, datasetType: DatasetType) -> tuple[DatasetRecordStorage, bool]:
         # Docstring inherited from DatasetRecordStorageManager.

python/lsst/daf/butler/registry/interfaces/_datasets.py

@@ -32,6 +32,7 @@
 import sqlalchemy.sql
 
 from ...core import DataCoordinate, DatasetId, DatasetRef, DatasetType, SimpleQuery, Timespan, ddl
+from .._exceptions import MissingDatasetTypeError
 from ._versioning import VersionedExtension
 
 if TYPE_CHECKING:
@@ -596,7 +597,7 @@ def __getitem__(self, name: str) -> DatasetRecordStorage:
         """
         result = self.find(name)
         if result is None:
-            raise KeyError(f"Dataset type with name '{name}' not found.")
+            raise MissingDatasetTypeError(f"Dataset type with name '{name}' not found.")
         return result
 
     @abstractmethod

python/lsst/daf/butler/registry/tests/_registry.py

@@ -67,6 +67,7 @@
     DatasetTypeError,
     InconsistentDataIdError,
     MissingCollectionError,
+    MissingDatasetTypeError,
     OrphanedRecordError,
 )
 from ..interfaces import ButlerAttributeExistsError, DatasetIdGenEnum
@@ -433,7 +434,7 @@ def testRemoveDatasetTypeSuccess(self):
         registry = self.makeRegistry()
         self.loadData(registry, "base.yaml")
         registry.removeDatasetType("flat")
-        with self.assertRaises(KeyError):
+        with self.assertRaises(MissingDatasetTypeError):
             registry.getDatasetType("flat")
 
     def testRemoveDatasetTypeFailure(self):