Support SQLite ALTER with batch feature during alembic migrate

Fix #404

migrations/env.py

@@ -73,6 +73,7 @@ def run_migrations_online():
     context.configure(connection=connection,
                       target_metadata=target_metadata,
                       process_revision_directives=process_revision_directives,
+                      render_as_batch=config.get_main_option('sqlalchemy.url').startswith('sqlite:'),
                       **current_app.extensions['migrate'].configure_args)
 
     try:

migrations/versions/1274ed462010_change_setting_value_data_type.py

@@ -33,8 +33,9 @@ def update_data():
     )
 
 def upgrade():
-    # change column data type
-    op.alter_column('setting', 'value', existing_type=sa.String(256), type_=sa.Text())
+    with op.batch_alter_table('setting') as batch_op:
+        # change column data type
+        batch_op.alter_column('value', existing_type=sa.String(256), type_=sa.Text())
     # update data for new schema
     update_data()
 
@@ -42,5 +43,6 @@ def upgrade():
 def downgrade():
     # delete added records in previous version
     op.execute("DELETE FROM setting WHERE id > 41")
-    # change column data type
-    op.alter_column('setting', 'value', existing_type=sa.Text(), type_=sa.String(256))
+    with op.batch_alter_table('setting') as batch_op:
+        # change column data type
+        batch_op.alter_column('value', existing_type=sa.Text(), type_=sa.String(256))

migrations/versions/1274ed462010_remove_all_settings_in_the_db.py

@@ -23,8 +23,10 @@ def upgrade():
     # written to the DB.
     op.execute("DELETE FROM setting")
 
-    # drop view column since we don't need it
-    op.drop_column('setting', 'view')
+    with op.batch_alter_table('setting') as batch_op:
+        # drop view column since we don't need it
+        batch_op.drop_column('view')
 
 def downgrade():
-    op.add_column('setting', sa.Column('view', sa.String(length=64), nullable=True))
+    with op.batch_alter_table('setting') as batch_op:
+        batch_op.add_column(sa.Column('view', sa.String(length=64), nullable=True))