Exception handling for database queries

ref-test/app/models/dataset.py

@@ -2,8 +2,8 @@ from ..extensions import db
 from ..tools.encryption import decrypt, encrypt
 from ..tools.logs import write
 
-from flask import flash
 from flask import current_app as app
+from flask.helpers import flash
 from flask_login import current_user
 from sqlalchemy.exc import SQLAlchemyError
 from werkzeug.utils import secure_filename
@@ -43,11 +43,13 @@ class Dataset(db.Model):
     def get_name(self): return decrypt(self.name)
 
     def make_default(self):
-        for dataset in Dataset.query.all():
-            dataset.default = False
-        self.default = True
         try:
-            db.session.commit()
+            for dataset in Dataset.query.all(): dataset.default = False
+        except SQLAlchemyError as exception:
+            write('system.log', f'Database error when setting default dataset {self.id}: {exception}')
+            return False, f'Database error {exception}.'
+        self.default = True
+        try: db.session.commit()
         except SQLAlchemyError as exception:
             db.session.rollback()
             write('system.log', f'Database error when setting default dataset {self.id}: {exception}')
@@ -61,10 +63,14 @@ class Dataset(db.Model):
             message = 'Cannot delete the default dataset.'
             flash(message, 'error')
             return False, message
-        if Dataset.query.count() == 1:
-            message = 'Cannot delete the only dataset.'
-            flash(message, 'error')
-            return False, message
+        try:
+            if Dataset.query.count() == 1:
+                message = 'Cannot delete the only dataset.'
+                flash(message, 'error')
+                return False, message
+        except SQLAlchemyError as exception:
+            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} deleted by {current_user.get_username()}.')
         filename = secure_filename('.'.join([self.id,'json']))
         data = Path(app.config.get('DATA'))