add migration script

core/admin/migrations/versions/fc099bd15cbe_.py

@@ -0,0 +1,65 @@
+"""change default unlimited value for max_users and max_aliases to -1
+
+Revision ID: fc099bd15cbe
+Revises: cd79ed46d9c2
+Create Date: 2019-01-06 13:40:23.372373
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = 'fc099bd15cbe'
+down_revision = 'cd79ed46d9c2'
+
+from alembic import op
+import sqlalchemy as sa
+
+
+domain_table = sa.Table(
+    'domain',
+    sa.MetaData(),
+    sa.Column('max_users', sa.Integer(), nullable=False),
+    sa.Column('max_aliases', sa.Integer(), nullable=False),
+)
+
+
+def upgrade():
+    connection = op.get_bind()
+    connection.execute(
+            domain_table.update().where(
+                domain_table.c.max_users == 0
+                ).values(
+                    max_users=-1
+                )
+            )
+    connection.execute(
+            domain_table.update().where(
+                domain_table.c.max_aliases == 0
+                ).values(
+                    max_aliases=-1
+                )
+            )
+    #set new unlimited default to -1
+    with op.batch_alter_table('domain') as batch:
+        batch.alter_column('max_users', server_default='-1')
+        batch.alter_column('max_aliases', server_default='-1')
+
+def downgrade():
+    connection = op.get_bind()
+    connection.execute(
+            domain_table.update().where(
+                domain_table.c.max_users == -1
+                ).values(
+                    max_users=0
+                )
+            )
+    connection.execute(
+            domain_table.update().where(
+                domain_table.c.max_aliases == -1
+                ).values(
+                    max_aliases=0
+                )
+            )
+    #set default to 0
+    with op.batch_alter_table('domain') as batch:
+        batch.alter_column('max_users', server_default='0')
+        batch.alter_column('max_aliases', server_default='0')