Create a slug for old orders in the migration

app/migrations/versions/29ccbe077c57_add_slug.py

@@ -12,12 +12,34 @@ down_revision = '55013fe95bea'
 
 from alembic import op
 import sqlalchemy as sa
+from sqlalchemy.sql import text
 
 def upgrade():
-    op.add_column('order', sa.Column('slug', sa.String(length=7), nullable=True))
-    op.create_unique_constraint(None, 'order', ['slug'])
+    op.add_column('order', sa.Column(
+        'slug',
+        sa.String(length=7),
+        nullable=False,
+        # Default: random alphanumerical string
+        server_default=text('SUBSTRING(MD5(RAND()) FROM 1 FOR 7)')
+    ))
+    op.create_unique_constraint('order_slug_unique', 'order', ['slug'])
+
+    # Trigger to handle duplicates: generate new slug if slug already exists
+    op.execute(text(
+        """
+        CREATE TRIGGER order_before_insert
+          BEFORE UPDATE ON `order`
+          FOR EACH ROW
+          BEGIN
+            WHILE (NEW.slug IS NULL OR (SELECT id FROM `order` WHERE slug = NEW.slug) IS NOT NULL) DO
+              SET NEW.slug = SUBSTRING(MD5(RAND()) FROM 1 FOR 7);
+            END WHILE;
+          END
+        """
+    ))
 
 
 def downgrade():
-    op.drop_constraint(None, 'order', type_='unique')
+    op.execute(text("DROP TRIGGER order_before_insert"))
+    op.drop_constraint('order_slug_unique', 'order', type_='unique')
     op.drop_column('order', 'slug')

app/models/order.py

@@ -2,7 +2,6 @@
 import typing
 from collections import defaultdict
 from datetime import datetime
-import secrets
 import string
 
 from hlds.definitions import location_definitions
@@ -12,11 +11,6 @@ from .database import db
 from .user import User
 
 
-def generate_slug():
-    alphabet = string.ascii_letters + string.digits
-    return ''.join(secrets.choice(alphabet) for i in range(7))
-
-
 class Order(db.Model):
     """Class used for configuring the Order model in the database"""
     id = db.Column(db.Integer, primary_key=True)
@@ -26,7 +20,9 @@ class Order(db.Model):
     starttime = db.Column(db.DateTime)
     stoptime = db.Column(db.DateTime)
     public = db.Column(db.Boolean, default=True)
-    slug = db.Column(db.String(7), default=generate_slug, unique=True)
+    # The default value for `slug`, a random 7-character alphanumerical string,
+    # is created on the database side. See migrations/versions/29ccbe077c57_add_slug.py
+    slug = db.Column(db.String(7), unique=True)
 
     items = db.relationship("OrderItem", backref="order", lazy="dynamic")