Use consistent error message for getURI if multiple URIs retrieved

python/lsst/daf/butler/_butler.py

@@ -930,11 +930,16 @@ def getURI(self, datasetRefOrType: Union[DatasetRef, DatasetType, str],
             differs from the one found in the registry.
         TypeError
             Raised if no collections were provided.
+        RuntimeError
+            Raised if a URI is requested for a dataset that consists of
+            multiple artifacts.
         """
-        primary, _ = self.getURIs(datasetRefOrType, dataId=dataId, predict=predict,
-                                  collections=collections, run=run, **kwds)
-        if primary is None:
-            raise RuntimeError(f"Found dataset but no single URI retrieved for it {datasetRefOrType}")
+        primary, components = self.getURIs(datasetRefOrType, dataId=dataId, predict=predict,
+                                           collections=collections, run=run, **kwds)
+
+        if primary is None or components:
+            raise RuntimeError(f"Dataset ({datasetRefOrType}) includes distinct URIs for components. "
+                               "Use Butler.getURIs() instead.")
         return primary
 
     def datasetExists(self, datasetRefOrType: Union[DatasetRef, DatasetType, str],

python/lsst/daf/butler/datastores/chainedDatastore.py

@@ -518,13 +518,16 @@ def getURI(self, ref: DatasetRef, predict: bool = False) -> ButlerURI:
         ------
         FileNotFoundError
             A URI has been requested for a dataset that does not exist and
-            guessing is not allowed.  Can also raise if the dataset is
-            present but it has been disassembled into multiple artifacts.
+            guessing is not allowed.
+        RuntimeError
+            Raised if a request is made for a single URI but multiple URIs
+            are associated with this dataset.
         """
         log.debug("Requesting URI for %s", ref)
-        primary, _ = self.getURIs(ref, predict)
-        if primary is None:
-            raise FileNotFoundError(f"Found dataset but no single URI possible for {ref}")
+        primary, components = self.getURIs(ref, predict)
+        if primary is None or components:
+            raise RuntimeError(f"Dataset ({ref}) includes distinct URIs for components. "
+                               "Use Dataastore.getURIs() instead.")
         return primary
 
     def remove(self, ref: DatasetRef) -> None:

python/lsst/daf/butler/datastores/fileLikeDatastore.py

@@ -914,19 +914,22 @@ def getURI(self, ref: DatasetRef, predict: bool = False) -> ButlerURI:
         Raises
         ------
         FileNotFoundError
-            A URI has been requested for a dataset that does not exist and
-            guessing is not allowed. Can also raise if the dataset is
-            present but it has been disassembled into multiple artifacts.
+            Raised if a URI has been requested for a dataset that does not
+            exist and guessing is not allowed.
+        RuntimeError
+            Raised if a request is made for a single URI but multiple URIs
+            are associated with this dataset.
 
         Notes
         -----
         When a predicted URI is requested an attempt will be made to form
         a reasonable URI based on file templates and the expected formatter.
         """
-        uri, components = self.getURIs(ref, predict)
-        if uri is None:
-            raise FileNotFoundError(f"Found dataset but no single URI possible for {ref}")
-        return uri
+        primary, components = self.getURIs(ref, predict)
+        if primary is None or components:
+            raise RuntimeError(f"Dataset ({ref}) includes distinct URIs for components. "
+                               "Use Dataastore.getURIs() instead.")
+        return primary
 
     def get(self, ref: DatasetRef, parameters: Optional[Mapping[str, Any]] = None) -> Any:
         """Load an InMemoryDataset from the store.

python/lsst/daf/butler/datastores/inMemoryDatastore.py

@@ -437,12 +437,15 @@ def getURI(self, ref: DatasetRef, predict: bool = False) -> ButlerURI:
         FileNotFoundError
             A URI has been requested for a dataset that does not exist and
             guessing is not allowed.
-
+        AssertionError
+            Raised if an internal error occurs.
         """
-        uri, _ = self.getURIs(ref, predict)
-        if uri is None:
-            raise RuntimeError(f"Unexpectedly got no URI for in-memory datastore for {ref}")
-        return uri
+        primary, _ = self.getURIs(ref, predict)
+        if primary is None:
+            # This should be impossible since this datastore does
+            # not disassemble. This check also helps mypy.
+            raise AssertionError(f"Unexpectedly got no URI for in-memory datastore for {ref}")
+        return primary
 
     def trash(self, ref: DatasetRef, ignore_errors: bool = False) -> None:
         """Indicate to the Datastore that a dataset can be removed.