On Mon, Oct 30, 2017 at 11:23 PM, <a...@riptideio.com> wrote:
> I have 2 migration scripts.
>
> The first 1 (base) is this
>
> from models import EntityProperty
> from contextlib import contextmanager
>
> # revision identifiers, used by Alembic.
> revision = 'ecbde8fa83e3'
> down_revision = None
> branch_labels = None
> depends_on = None
>
> from alembic import op # noqa
> import sqlalchemy as sa # noqa
>
>
> @contextmanager
> def session_scope():
> session = sa.orm.session.Session(bind=op.get_bind())
> try:
> yield session
> session.commit()
> except:
> session.rollback()
> raise
> finally:
> session.close()
>
>
> def _upgrade(session):
> properties = session.query(EntityProperty).filter(
> ~EntityProperty._ptype.in_(["AI", "AO", "AV"])
> ).all()
>
> for _property in properties:
> _property._cov_increment = None
>
>
> def upgrade():
> with session_scope() as session:
> _upgrade(session)
>
>
> def downgrade():
> pass
>
>
> This script queries the EntityPropertyTable and does some op on it.
>
> The second migration script is
>
> revision = 'ab47480a7be7'
> down_revision = u'ecbde8fa83e3'
> branch_labels = None
> depends_on = None
>
> from alembic import op # noqa
> import sqlalchemy as sa # noqa
>
>
> def upgrade():
> # add bacnet_enable to EP
> with op.batch_alter_table(u'entityproperties', schema=None) as batch_op:
> batch_op.execute("PRAGMA foreign_keys=OFF;")
> batch_op.add_column(
> sa.Column(
> 'bacnet_object', sa.Boolean(), nullable=True,
> server_default=expression.true()))
>
>
> def downgrade():
> with op.batch_alter_table(u'entityproperties', schema=None) as batch_op:
> batch_op.drop_column('bacnet_object')
>
>
> This script does operate in batch mode and adds a column called
> 'bacnet_object' to the EntityProperty table.
>
> Now when I try to downgrade to base 'downgrade -r base' I get the following
> error
>
> no such column: entityproperties.bacnet_object
>
> This error is while executing script 1. The execution of script 2 does
> proceeds without any issues. When I look up the generated SQL for script1 I
> find this in the SQL statement
> Enter code here..
> entityproperties.bacnet_object AS entityproperties_bacnet_object
>
> The downgrade of script2 does indeed removes the bacnet_object column from
> the entityproperty table. Why the SQL generated for script1 is still looking
> for bacnet_object column in the EntityProperty table?
This would mean your mappings used in script #1 still include the
bacnet_object column.
You haven't given me any information on how EntityProperty gets
created but it would appear that it runs table reflection upon import.
This import would occur before any migration script runs, so when
script 2 drops the column you now have a stale mapping.
The general antipattern here is that you're referring to your
application's models within a migration script. Since each migration
file represents a point in time of your schema design, one that might
be very different from what the current model is, to run any SQL
queries in a migration file you should create Table metadata directly
in the migration that explicitly includes the tables and columns you
need to query against, which would always exist as of that migration
version.
>
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