On 8/11/15 7:12 PM, c.bu...@posteo.jp wrote:
I want to add a new column which is a many-to-many relation to a new
created table. I am not sure what is wrong with the code below.
#!/usr/bin/env python3
# -*- coding: utf-8 -*-
import sqlalchemy as sa
import sqlalchemy.orm as sao
import sqlalchemy.ext.declarative as sad
import sqlalchemy_utils as su
import alembic
import alembic.operations
import alembic.migration
_Base = sad.declarative_base()
# a simple model
class Model(_Base):
__tablename__ = 'Model'
_oid = sa.Column('oid', sa.Integer, primary_key=True)
_simple = sa.Column('simple', sa.Integer)
# engine
engine = sa.create_engine('sqlite:///mig2.db', echo = True)
# create database if needed
if not su.database_exists(engine.url):
su.create_database(engine.url) # create the database
_Base.metadata.create_all(engine) # create the table in the
db
# another model
class Sub(_Base):
__tablename__ = 'Sub'
_oid = sa.Column('oid', sa.Integer, primary_key=True)
_somedata = sa.Column('simple', sa.Integer)
# many-to-many-relation
model_sub_relation = sa.Table('model_sub_relation', _Base.metadata,
sa.Column('model_oid', sa.Integer, sa.ForeignKey('Model.oid')),
sa.Column('sub_oid', sa.Integer, sa.ForeignKey('Sub.oid'))
)
conn = engine.connect()
ctx = alembic.migration.MigrationContext.configure(conn)
op = alembic.operations.Operations(ctx)
op.create_table('Sub',
sa.Column('oid', sa.Integer, primary_key=True),
sa.Column('simple', sa.Integer)
)
op.add_column('Model', sao.relationship('subs',
secondary=model_sub_relation, backref='Model'))
a relationship() is not a Column. Alembic "add_column()" is intended
to render an "ALTER TABLE <foo> ADD COLUMN <bar>" statement. You need
to pass it a Column object.
Here you see the error message.
Traceback (most recent call last):
File "./mig2.py", line 54, in <module>
op.add_column('Model', sao.relationship('subs',
secondary=model_sub_relation, backref='Model')) File
"/usr/local/lib/python3.4/dist-packages/alembic/operations.py", line
592, in add_column t = self._table(table_name, column, schema=schema)
File "/usr/local/lib/python3.4/dist-packages/alembic/operations.py",
line 149, in _table t = sa_schema.Table(name, m, *columns, **kw) File
"/usr/local/lib/python3.4/dist-packages/sqlalchemy/sql/schema.py", line
416, in __new__ metadata._remove_table(name, schema) File
"/usr/local/lib/python3.4/dist-packages/sqlalchemy/util/langhelpers.py",
line 60, in __exit__ compat.reraise(exc_type, exc_value, exc_tb) File
"/usr/local/lib/python3.4/dist-packages/sqlalchemy/util/compat.py",
line 182, in reraise raise value File
"/usr/local/lib/python3.4/dist-packages/sqlalchemy/sql/schema.py", line
411, in __new__ table._init(name, metadata, *args, **kw) File
"/usr/local/lib/python3.4/dist-packages/sqlalchemy/sql/schema.py", line
488, in _init self._init_items(*args) File
"/usr/local/lib/python3.4/dist-packages/sqlalchemy/sql/schema.py", line
72, in _init_items item._set_parent_with_dispatch(self) File
"/usr/local/lib/python3.4/dist-packages/sqlalchemy/util/langhelpers.py",
line 833, in __getattr__ return self._fallback_getattr(key) File
"/usr/local/lib/python3.4/dist-packages/sqlalchemy/util/langhelpers.py",
line 811, in _fallback_getattr raise AttributeError(key)
AttributeError: _set_parent_with_dispatch
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