Exception handling for database commit operations

ref-test/app/models/dataset.py

@@ -5,6 +5,7 @@ from ..tools.logs import write
 from flask import flash
 from flask import current_app as app
 from flask_login import current_user
+from sqlalchemy.exc import SQLAlchemyError
 from werkzeug.utils import secure_filename
 
 from datetime import datetime
@@ -45,7 +46,12 @@ class Dataset(db.Model):
         for dataset in Dataset.query.all():
             dataset.default = False
         self.default = True
-        db.session.commit()
+        try:
+            db.session.commit()
+        except SQLAlchemyError as exception:
+            db.session.rollback()
+            write('system.log', f'Database error when setting default dataset {self.id}: {exception}')
+            return False, f'Database error {exception}.'
         write('system.log', f'Dataset {self.id} set as default by {current_user.get_username()}.')
         flash(message='Dataset set as default.', category='success')
         return True, f'Dataset set as default.'
@@ -63,9 +69,14 @@ class Dataset(db.Model):
         filename = secure_filename('.'.join([self.id,'json']))
         data = Path(app.config.get('DATA'))
         file_path = path.join(data, 'questions', filename)
+        try:
+            db.session.delete(self)
+            db.session.commit()
+        except SQLAlchemyError as exception:
+            db.session.rollback()
+            write('system.log', f'Database error when trying to delete dataset {self.id}: {exception}')
+            return False, f'Database error: {exception}'
         remove(file_path)
-        db.session.delete(self)
-        db.session.commit()
         return True, 'Dataset deleted.'
     
     def create(self, data:list, default:bool=False):
@@ -78,8 +89,13 @@ class Dataset(db.Model):
         self.creator = current_user
         if default: self.make_default()
         write('system.log', f'New dataset {self.get_name()} added by {current_user.get_username()}.')
-        db.session.add(self)
-        db.session.commit()
+        try:
+            db.session.add(self)
+            db.session.commit()
+        except SQLAlchemyError as exception:
+            db.session.rollback()
+            write('system.log', f'Database error when trying to crreate dataset {self.id}: {exception}')
+            return False, f'Database error: {exception}'
         return True, 'Dataset created.'
 
     def check_file(self):
@@ -103,6 +119,11 @@ class Dataset(db.Model):
             dump(data, file, indent=2)
         write('system.log', f'Dataset {self.id} edited by {current_user.get_username()}.')
         flash(f'Dataset {self.get_name()} successfully edited.', 'success')
-        db.session.add(self)
-        db.session.commit()
+        try:
+            db.session.add(self)
+            db.session.commit()
+        except SQLAlchemyError as exception:
+            db.session.rollback()
+            write('system.log', f'Database error when trying to update dataset {self.id}: {exception}')
+            return False, f'Database error: {exception}'
         return True, 'Dataset successfully edited.'