Exception handling for database queries

ref-test/app/quiz/views.py

@@ -1,10 +1,12 @@
 from ..forms.quiz import StartQuiz
 from ..models import Entry, Test
 from ..tools.forms import send_errors_to_client
+from ..tools.logs import write
 from ..tools.test import redirect_if_started
 
-from flask import abort, Blueprint, jsonify, redirect, render_template, request, session
-from flask.helpers import flash, url_for
+from flask import Blueprint, jsonify, render_template, request, session
+from flask.helpers import abort, flash, redirect, url_for
+from sqlalchemy.exc import SQLAlchemyError
 
 from datetime import datetime
 
@@ -37,7 +39,10 @@ def _start():
             entry.set_club(request.form.get('club'))
             entry.set_email(request.form.get('email'))
             code = request.form.get('test_code').replace('—', '').lower()
-            test = Test.query.filter_by(code=code).first()
+            try: test = Test.query.filter_by(code=code).first()
+            except SQLAlchemyError as exception:
+                write('system.log', f'Database error when processing request \'{request.url}\': {exception}')
+                return abort(500)
             entry.test = test
             entry.user_code = request.form.get('user_code')
             entry.user_code = None if entry.user_code == '' else entry.user_code.lower()
@@ -59,16 +64,23 @@ def _start():
 @quiz.route('/quiz/')
 def _quiz():
     id = session.get('id')
-    if not id or not Entry.query.filter_by(id=id).first():
-        flash('Your session was not recognised. Please sign in to the quiz again.', 'error')
-        session.pop('id', None)
-        return redirect(url_for('quiz._start'))
+    try:
+        if not id or not Entry.query.filter_by(id=id).first():
+            flash('Your session was not recognised. Please sign in to the quiz again.', 'error')
+            session.pop('id', None)
+            return redirect(url_for('quiz._start'))
+    except SQLAlchemyError as exception:
+        write('system.log', f'Database error when processing request \'{request.url}\': {exception}')
+        return abort(500)
     return render_template('/quiz/client.html')
 
 @quiz.route('/result/')
 def _result():
     id = session.get('id')
-    entry = Entry.query.filter_by(id=id).first()
+    try: entry = Entry.query.filter_by(id=id).first()
+    except SQLAlchemyError as exception:
+        write('system.log', f'Database error when processing request \'{request.url}\': {exception}')
+        return abort(500)
     if not entry: return abort(404)
     session.pop('id',None)
     score = round(100*entry.result['score']/entry.result['max'])