Exception handling for database commit operations

ref-test/app/models/entry.py

@@ -7,6 +7,7 @@ from .test import Test
 from flask_login import current_user
 from flask_mail import Message
 from smtplib import SMTPException
+from sqlalchemy.exc import SQLAlchemyError
 
 from datetime import datetime, timedelta
 from uuid import uuid4
@@ -70,23 +71,32 @@ class Entry(db.Model):
 
     def ready(self):
         self.generate_id()
-        db.session.add(self)
-        db.session.commit()
-        write('tests.log', f'New test ready for {self.get_first_name()} {self.get_surname()}.')
+        try:
+            db.session.add(self)
+            db.session.commit()
+        except SQLAlchemyError as exception:
+            db.session.rollback()
+            write('system.log', f'Database error when preparing new entry for {self.get_surname()}, {self.get_first_name()}: {exception}')
+            return False, f'Database error: {exception}'
+        write('tests.log', f'New test ready for {self.get_surname()}, {self.get_first_name()} with id {self.id}.')
         return True, f'Test ready.'
 
     def start(self):
         self.start_time = datetime.now()
         self.status = 'started'
-        write('tests.log', f'Test started by {self.get_first_name()} {self.get_surname()}.')
-        db.session.commit()
+        try:
+            db.session.commit()
+        except SQLAlchemyError as exception:
+            db.session.rollback()
+            write('system.log', f'Database error when starting test for {self.get_surname()}, {self.get_first_name()}: {exception}')
+            return False, f'Database error: {exception}'
+        write('tests.log', f'Test started by {self.get_surname()}, {self.get_first_name()} with id {self.id}.')
         return True, f'New test started with id {self.id}.'
 
     def complete(self, answers:dict=None, result:dict=None):
         self.end_time = datetime.now()
         self.answers = answers
         self.result = result
-        write('tests.log', f'Test completed by {self.get_first_name()} {self.get_surname()}.')
         delta = timedelta(minutes=int(0 if self.test.time_limit is None else self.test.time_limit)+1)
         if not self.test.time_limit or self.end_time <= self.start_time + delta:
             self.status = 'completed'
@@ -94,7 +104,13 @@ class Entry(db.Model):
         else:
             self.status = 'late'
             self.valid = False
-        db.session.commit()
+        try:
+            db.session.commit()
+        except SQLAlchemyError as exception:
+            db.session.rollback()
+            write('system.log', f'Database error when submitting entry for {self.get_surname()}, {self.get_first_name()}: {exception}')
+            return False, f'Database error: {exception}'
+        write('tests.log', f'Test completed by {self.get_surname()}, {self.get_first_name()} with id {self.id}.')
         return True, f'Test entry completed for id {self.id}.'
 
     def validate(self):
@@ -102,15 +118,25 @@ class Entry(db.Model):
         if self.status == 'started': return False, 'The entry is still pending.'
         self.valid = True
         self.status = 'completed'
-        db.session.commit()
+        try:
+            db.session.commit()
+        except SQLAlchemyError as exception:
+            db.session.rollback()
+            write('system.log', f'Database error when validating entry {self.id}: {exception}')
+            return False, f'Database error: {exception}'
         write('system.log', f'The entry {self.id} has been validated by {current_user.get_username()}.')
         return True, f'The entry {self.id} has been validated.'
 
     def delete(self):
         id = self.id
         name = f'{self.get_first_name()} {self.get_surname()}'
-        db.session.delete(self)
-        db.session.commit()
+        try:
+            db.session.delete(self)
+            db.session.commit()
+        except SQLAlchemyError as exception:
+            db.session.rollback()
+            write('system.log', f'Database error when deleting entry {id}: {exception}')
+            return False, f'Database error: {exception}'
         write('system.log', f'The entry {id} by {name} has been deleted by {current_user.get_username()}.')
         return True, 'Entry deleted.'