diff --git a/buildingmotif/database/table_connection.py b/buildingmotif/database/table_connection.py
index b1ce2f7a9..e18659fa5 100644
--- a/buildingmotif/database/table_connection.py
+++ b/buildingmotif/database/table_connection.py
@@ -13,6 +13,7 @@
     DBTemplate,
     DepsAssociation,
 )
+from buildingmotif.database.errors import LibraryNotFound, TemplateNotFound
 
 
 class TableConnection:
@@ -216,7 +217,10 @@ def get_db_library(self, id: int) -> DBLibrary:
         :return: DBLibrary
         :rtype: DBLibrary
         """
-        db_library = self.bm.session.query(DBLibrary).filter(DBLibrary.id == id).one()
+        try:
+            db_library = self.bm.session.query(DBLibrary).filter(DBLibrary.id == id).one()
+        except NoResultFound:
+            raise LibraryNotFound(f"Library with id {id} not found")
         return db_library
 
     def get_db_library_by_name(self, name: str) -> DBLibrary:
@@ -298,9 +302,12 @@ def get_db_template(self, id: int) -> DBTemplate:
         :return: DBTemplate
         :rtype: DBTemplate
         """
-        db_template = (
-            self.bm.session.query(DBTemplate).filter(DBTemplate.id == id).one()
-        )
+        try:
+            db_template = (
+                self.bm.session.query(DBTemplate).filter(DBTemplate.id == id).one()
+            )
+        except NoResultFound:
+            raise TemplateNotFound(idnum=id)
         return db_template
 
     def get_db_template_by_name(self, name: str) -> DBTemplate:
@@ -316,7 +323,7 @@ def get_db_template_by_name(self, name: str) -> DBTemplate:
                 self.bm.session.query(DBTemplate).filter(DBTemplate.name == name).one()
             )
         except NoResultFound:
-            raise NoResultFound(f"No template found with name {name}")
+            raise TemplateNotFound(name=name)
         return db_template
 
     def get_library_defining_db_template(self, id: int) -> DBLibrary:
diff --git a/buildingmotif/dataclasses/library.py b/buildingmotif/dataclasses/library.py
index d0bf70ead..d12afa07b 100644
--- a/buildingmotif/dataclasses/library.py
+++ b/buildingmotif/dataclasses/library.py
@@ -313,7 +313,6 @@ def _infer_templates_from_graph(self, graph: rdflib.Graph):
                 logging.warning(
                     f"An ontology could not resolve a dependency on {dependency} ({e}). Check this is loaded into BuildingMOTIF"
                 )
-                get_building_motif().session.rollback()
                 continue
         class_candidates = set(graph.subjects(rdflib.RDF.type, rdflib.OWL.Class))
         shape_candidates = set(graph.subjects(rdflib.RDF.type, rdflib.SH.NodeShape))