SQLAlchemy di Python non pulisce la tabella secondaria (molti-a-molti)?

Question

Ho una relazione molti-a-molti tra User s e Task s. Voglio che la "tabella secondaria" (ovvero la tabella che facilita la relazione molti-a-molti) venga eliminata quando elimino uno Task o User. Come posso configurare SQLAlchemy per questo?

Ecco alcuni esempi di codice Python che dimostrano il problema che sto avendo. Nota: questo codice è completamente autonomo e richiede solo il modulo sqlalchemy. Se copi e incolli questo codice, dovresti essere in grado di eseguirlo senza effetti collaterali e vedere lo stesso comportamento tu stesso. L'ultima riga dello script mostra che la riga pertinente nella "tabella secondaria" non è stata rimossa quando ho rimosso l'attività corrispondente. Tutte le asserzioni passano in questo esempio.

from sqlalchemy import create_engine, Column, Integer, Text, Table, ForeignKey 
from sqlalchemy.ext.declarative import declarative_base 
from sqlalchemy.orm import Session, relationship 

Model = declarative_base() 

class User(Model): 
    __tablename__ = 'users' 
    id = Column('user_id', Integer, primary_key=True) 
    email = Column('email', Text, unique=True) 

    def __init__(self, email): 
     self.email = email 

user_tasks = Table('user_tasks', Model.metadata, 
    Column('user_id', Integer, ForeignKey('users.user_id')), 
    Column('task_id', Integer, ForeignKey('tasks.task_id'))) 

class Task(Model): 
    __tablename__ = 'tasks' 
    id = Column('task_id', Integer, primary_key=True) 
    description = Column('description', Text) 
    assigned_to = relationship('User', secondary=user_tasks, backref='tasks') 

    def __init__(self, description): 
     self.description = description 

if __name__ == '__main__': 
    engine = create_engine('sqlite:///:memory:') 
    Model.metadata.create_all(engine) 
    s = Session(engine) 
    the_user = User('user') 
    s.add(the_user) 
    s.commit() 
    assert s.query(User).all() == [the_user] 
    user_task = Task('user_one task') 
    user_task.assigned_to.append(the_user) 
    s.add(user_task) 
    s.commit() 
    assert s.query(Task).all() == [user_task] 
    assert s.query(user_tasks).all() == [(1,1)] 
    s.query(Task).delete() 
    s.commit() 
    assert s.query(Task).all() == [] 
    assert s.query(User).all() == [the_user] 
    assert s.query(user_tasks).all() == [(1,1)] # I was expecting [] . 

Answer 1

Vedi delete(synchronize_session='evaluate'):

Il metodo non offre in Python cascata di relazioni - si presume che ON DELETE CASCADE è configurato per tutti i riferimenti di chiave esterna che lo richiedono. La sessione deve essere scaduta (si verifica automaticamente dopo commit() o chiama expire_all()) affinché lo stato degli oggetti dipendenti soggetti a delete o delete-orphan cascade sia rappresentato correttamente.

Cioè, SQLAlchemy non è in grado di trovare tutte le attività gli oggetti che stai cancellando e capire ogni riga da cancellare dalla user_tasks - il modo migliore per farlo è quello di utilizzare ON DELETE CASCADE sul estera chiavi (non funziona con le tabelle MyISAM MySQL o SQLite se chiavi esterne non sono abilitati):

http://docs.sqlalchemy.org/en/latest/core/constraints.html#on-update-and-on-delete

Answer 2

Quando ho provato il codice con sqlite sua non dare l'errore, ma quando ho provato con MySQL base di dati ho ottenuto l'errore

2012-03-29 10:43:15,330 INFO sqlalchemy.engine.base.Engine SELECT DATABASE() 
2012-03-29 10:43:15,331 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,332 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'character_set%%' 
2012-03-29 10:43:15,332 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,333 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'lower_case_table_names' 
2012-03-29 10:43:15,333 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,334 INFO sqlalchemy.engine.base.Engine SHOW COLLATION 
2012-03-29 10:43:15,334 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,337 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'sql_mode' 
2012-03-29 10:43:15,338 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,339 INFO sqlalchemy.engine.base.Engine DESCRIBE `user_tasks` 
2012-03-29 10:43:15,339 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,355 INFO sqlalchemy.engine.base.Engine DESCRIBE `users` 
2012-03-29 10:43:15,355 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,356 INFO sqlalchemy.engine.base.Engine DESCRIBE `tasks` 
2012-03-29 10:43:15,356 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,357 INFO sqlalchemy.engine.base.Engine 
DROP TABLE user_tasks 
2012-03-29 10:43:15,357 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,439 INFO sqlalchemy.engine.base.Engine COMMIT 
2012-03-29 10:43:15,440 INFO sqlalchemy.engine.base.Engine 
DROP TABLE users 
2012-03-29 10:43:15,440 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,573 INFO sqlalchemy.engine.base.Engine COMMIT 
2012-03-29 10:43:15,573 INFO sqlalchemy.engine.base.Engine 
DROP TABLE tasks 
2012-03-29 10:43:15,573 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,623 INFO sqlalchemy.engine.base.Engine COMMIT 
2012-03-29 10:43:15,624 INFO sqlalchemy.engine.base.Engine DESCRIBE `tasks` 
2012-03-29 10:43:15,624 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,632 INFO sqlalchemy.engine.base.Engine ROLLBACK 
2012-03-29 10:43:15,633 INFO sqlalchemy.engine.base.Engine DESCRIBE `users` 
2012-03-29 10:43:15,633 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,634 INFO sqlalchemy.engine.base.Engine ROLLBACK 
2012-03-29 10:43:15,634 INFO sqlalchemy.engine.base.Engine DESCRIBE `user_tasks` 
2012-03-29 10:43:15,634 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,635 INFO sqlalchemy.engine.base.Engine ROLLBACK 
2012-03-29 10:43:15,635 INFO sqlalchemy.engine.base.Engine 
CREATE TABLE tasks (
    task_id INTEGER NOT NULL AUTO_INCREMENT, 
    description TEXT, 
    PRIMARY KEY (task_id) 
) 


2012-03-29 10:43:15,635 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,732 INFO sqlalchemy.engine.base.Engine COMMIT 
2012-03-29 10:43:15,733 INFO sqlalchemy.engine.base.Engine 
CREATE TABLE users (
    user_id INTEGER NOT NULL AUTO_INCREMENT, 
    email VARCHAR(20), 
    PRIMARY KEY (user_id), 
    UNIQUE (email) 
) 


2012-03-29 10:43:15,733 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,841 INFO sqlalchemy.engine.base.Engine COMMIT 
2012-03-29 10:43:15,842 INFO sqlalchemy.engine.base.Engine 
CREATE TABLE user_tasks (
    user_id INTEGER, 
    task_id INTEGER, 
    FOREIGN KEY(user_id) REFERENCES users (user_id), 
    FOREIGN KEY(task_id) REFERENCES tasks (task_id) 
) 


2012-03-29 10:43:15,842 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:15,959 INFO sqlalchemy.engine.base.Engine COMMIT 
2012-03-29 10:43:15,964 INFO sqlalchemy.engine.base.Engine BEGIN (implicit) 
2012-03-29 10:43:15,965 INFO sqlalchemy.engine.base.Engine INSERT INTO users (email) VALUES (%s) 
2012-03-29 10:43:15,965 INFO sqlalchemy.engine.base.Engine ('user',) 
2012-03-29 10:43:15,966 INFO sqlalchemy.engine.base.Engine COMMIT 
2012-03-29 10:43:16,010 INFO sqlalchemy.engine.base.Engine BEGIN (implicit) 
2012-03-29 10:43:16,010 INFO sqlalchemy.engine.base.Engine SELECT users.user_id AS users_user_id, users.email AS users_email 
FROM users 
2012-03-29 10:43:16,011 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:16,013 INFO sqlalchemy.engine.base.Engine INSERT INTO tasks (description) VALUES (%s) 
2012-03-29 10:43:16,014 INFO sqlalchemy.engine.base.Engine ('user_one task',) 
2012-03-29 10:43:16,015 INFO sqlalchemy.engine.base.Engine INSERT INTO user_tasks (user_id, task_id) VALUES (%s, %s) 
2012-03-29 10:43:16,016 INFO sqlalchemy.engine.base.Engine (1L, 1L) 
2012-03-29 10:43:16,016 INFO sqlalchemy.engine.base.Engine COMMIT 
2012-03-29 10:43:16,085 INFO sqlalchemy.engine.base.Engine BEGIN (implicit) 
2012-03-29 10:43:16,086 INFO sqlalchemy.engine.base.Engine SELECT tasks.task_id AS tasks_task_id, tasks.description AS tasks_description 
FROM tasks 
2012-03-29 10:43:16,086 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:16,087 INFO sqlalchemy.engine.base.Engine SELECT user_tasks.user_id AS user_tasks_user_id, user_tasks.task_id AS user_tasks_task_id 
FROM user_tasks 
2012-03-29 10:43:16,088 INFO sqlalchemy.engine.base.Engine() 
2012-03-29 10:43:16,089 INFO sqlalchemy.engine.base.Engine SELECT user_tasks.user_id AS user_tasks_user_id, user_tasks.task_id AS user_tasks_task_id 
FROM user_tasks 
2012-03-29 10:43:16,089 INFO sqlalchemy.engine.base.Engine() 
[(1L, 1L)] 
2012-03-29 10:43:16,091 INFO sqlalchemy.engine.base.Engine DELETE FROM tasks 
2012-03-29 10:43:16,091 INFO sqlalchemy.engine.base.Engine() 
Traceback (most recent call last): 
    File "/tmp/test2.py", line 46, in <module> 
    s.query(Task).delete() 
    File "/home/npatel/.local/lib/python2.7/site-packages/sqlalchemy/orm/query.py", line 2283, in delete 
    result = session.execute(delete_stmt, params=self._params) 
    File "/home/npatel/.local/lib/python2.7/site-packages/sqlalchemy/orm/session.py", line 762, in execute 
    clause, params or {}) 
    File "/home/npatel/.local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1399, in execute 
    params) 
    File "/home/npatel/.local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1532, in _execute_clauseelement 
    compiled_sql, distilled_params 
    File "/home/npatel/.local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1640, in _execute_context 
    context) 
    File "/home/npatel/.local/lib/python2.7/site-packages/sqlalchemy/engine/base.py", line 1633, in _execute_context 
    context) 
    File "/home/npatel/.local/lib/python2.7/site-packages/sqlalchemy/engine/default.py", line 325, in do_execute 
    cursor.execute(statement, parameters) 
    File "/usr/lib64/python2.7/site-packages/MySQLdb/cursors.py", line 174, in execute 
    self.errorhandler(self, exc, value) 
    File "/usr/lib64/python2.7/site-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler 
    raise errorclass, errorvalue 
sqlalchemy.exc.IntegrityError: (IntegrityError) (1451, 'Cannot delete or update a parent row: a foreign key constraint fails (`test1`.`user_tasks`, CONSTRAINT `user_tasks_ibfk_2` FOREIGN KEY (`task_id`) REFERENCES `tasks` (`task_id`))') 'DELETE FROM tasks'() 

Così, dopo che sono venuto a sapere che sqlite non mantengono vincolo di chiave esterna . Ora cambio il tuo codice e controllo l'output.

from sqlalchemy import create_engine, Column, Integer, Text, Table, ForeignKey, String 
from sqlalchemy.ext.declarative import declarative_base 
from sqlalchemy.orm import Session, relationship 

Model = declarative_base() 


class User(Model): 
    __tablename__ = 'users' 
    id = Column('user_id', Integer, primary_key=True) 
    email = Column('email', String(length=20), unique=True) 

    def __init__(self, email): 
     self.email = email 

user_tasks = Table('user_tasks', Model.metadata, 
    Column('user_id', Integer, ForeignKey('users.user_id')), 
    Column('task_id', Integer, ForeignKey('tasks.task_id'))) 


class Task(Model): 
    __tablename__ = 'tasks' 
    id = Column('task_id', Integer, primary_key=True) 
    description = Column('description', Text) 
    assigned_to = relationship('User', secondary=user_tasks, backref='tasks') 

    def __init__(self, description): 
     self.description = description 

if __name__ == '__main__': 
    engine = create_engine('mysql://test:test@localhost/test', echo=True) 
    Model.metadata.drop_all(engine) 
    Model.metadata.create_all(engine) 
    s = Session(engine) 
    the_user = User('user') 
    s.add(the_user) 
    s.commit() 
    assert s.query(User).all() == [the_user] 
    user_task = Task('user_one task') 
    user_task.assigned_to.append(the_user) 
    s.add(user_task) 
    s.commit() 
    assert s.query(Task).all() == [user_task] 
    assert s.query(user_tasks).all() == [(1, 1)] 
    the_user.tasks = [] 
    s.query(Task).delete() 
    s.commit() 
    assert s.query(Task).all() == [] 
    assert s.query(User).all() == [the_user] 
    assert s.query(user_tasks).all() == [(1,1)] # I was expecting [] .