server/db: fix user cascade deletions

server/szurubooru/db/post.py

@@ -136,7 +136,12 @@ class Post(Base):
 
     # basic meta
     post_id = Column('id', Integer, primary_key=True)
-    user_id = Column('user_id', Integer, ForeignKey('user.id'), index=True)
+    user_id = Column(
+        'user_id',
+        Integer,
+        ForeignKey('user.id', ondelete='SET NULL'),
+        nullable=True,
+        index=True)
     version = Column('version', Integer, default=1, nullable=False)
     creation_time = Column('creation_time', DateTime, nullable=False)
     last_edit_time = Column('last_edit_time', DateTime)

server/szurubooru/db/snapshot.py

@@ -18,7 +18,8 @@ class Snapshot(Base):
     resource_id = Column('resource_id', Integer, nullable=False, index=True)
     resource_repr = Column('resource_repr', Unicode(64), nullable=False)
     operation = Column('operation', Unicode(16), nullable=False)
-    user_id = Column('user_id', Integer, ForeignKey('user.id'))
+    user_id = Column(
+        'user_id', Integer, ForeignKey('user.id', ondelete='set null'))
     data = Column('data', PickleType)
 
     user = relationship('User')

server/szurubooru/migrations/versions/840b460c5613_fix_foreignkeys.py

@@ -0,0 +1,33 @@
+'''
+Fix ForeignKey constraint definitions
+
+Revision ID: 840b460c5613
+Created at: 2016-08-15 18:39:30.909867
+'''
+
+import sqlalchemy as sa
+from alembic import op
+
+
+revision = '840b460c5613'
+down_revision = '7f6baf38c27c'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    op.drop_constraint('post_user_id_fkey', 'post', type_='foreignkey')
+    op.drop_constraint('snapshot_user_id_fkey', 'snapshot', type_='foreignkey')
+    op.create_foreign_key(
+        None, 'post', 'user', ['user_id'], ['id'], ondelete='SET NULL')
+    op.create_foreign_key(
+        None, 'snapshot', 'user', ['user_id'], ['id'], ondelete='set null')
+
+
+def downgrade():
+    op.drop_constraint(None, 'snapshot', type_='foreignkey')
+    op.drop_constraint(None, 'post', type_='foreignkey')
+    op.create_foreign_key(
+        'snapshot_user_id_fkey', 'snapshot', 'user', ['user_id'], ['id'])
+    op.create_foreign_key(
+        'post_user_id_fkey', 'post', 'user', ['user_id'], ['id'])