如何在sqlite alembic迁移中迁移数据？

Question

I have a column goods.visible (boolean) and i want to replace it with goods.status (enum).

I need to replace one column with another and migrate data using sqlalchemy (to use its data type conversion mechanism). As sqlite does not support ALTER TABLE for this, I have to use batch_alter_table alembic operation for this.

My migration looks like the following. It throws sqlite3.OperationalError: no such column: goods.status , because in my old table there is no such column (new table is created for migration using batch)

def upgrade():
    with op.batch_alter_table('goods') as batch_op:
        batch_op.add_column(sa.Column('status', sa.Enum('published', 'unpublished', 'deleted'), nullable=True))

        conn = op.get_bind()
        Session = sa.orm.sessionmaker()
        session = Session(bind=conn)
        for good in session.query(Good):
            # I want to perform some data updates & insert data into new column
        batch_op.drop_column('visible')

If i will add load_only to specify columns to be selected from the table: sqlite3.OperationalError: no such column: goods.status

i will get error sqlalchemy.exc.ArgumentError: Can't find property named 'visible' on the mapped entity Mapper|Good|goods in this Query. . I understand why i get it - i have no more property visible in my model.

How i can migrate data using alembic in this case?

I tried to use raw queries.. but it says there is no table:

    s = sa.sql.select([sa.sql.text('goods.*')])
    for row in conn.execute(s):
        print(row)

Hovewer inspector displays goods table:

 inspector = sa.inspect(conn.engine)
    for table_name in inspector.get_table_names():
        print(table_name)
        for column in inspector.get_columns(table_name):
            print("Column: %s" % column['name'])

Displays

goods
Column: id
Column: name
Column: price
Column: visible

Answer 1

You can have multiple batch_alter_table blocks. Use the first one to add the new column, then (outside and after the block) run your business logic (in this case conversion of your boolean value to some enum values), then use another block to drop the column.

Something like:-

def upgrade():
    with op.batch_alter_table('goods') as batch_op:
        batch_op.add_column(sa.Column('status', sa.Enum('published', 'unpublished', 'deleted'), nullable=True))
    # Do your business logic here
    with op.batch_alter_table('goods') as batch_op:
        batch_op.drop_column('visible')