SQLAlchemy 多对多 UNIQUE 约束关联失败 table

Question

我把tables 'projects'和'project_freelancer'通过多对多的关系连接起来，因为一个项目可以有多个freelancer，一个freelancer可以做多个项目。在 'projects' 中我只有一个主键 'url'。在 'projects_freelancer' 中，我有一个来自 'url' 和 'freel_url'

的复合主键

因此我这样定义我的协会table：

association_table = Table('association', Base.metadata,
                          Column('projects_url', ForeignKey('projects.url', ondelete="CASCADE"), primary_key=True),
                          Column('project_freelancer_url'),
                          Column('project_freelancer_freel_url'),
                          ForeignKeyConstraint(
                              ('project_freelancer_url', 'project_freelancer_freel_url'),
                              ('project_freelancer.url', 'project_freelancer.freel_url')),
                          )

这是我的 class-定义（简短版）：

class Project(Base):
    __tablename__ = "projects"

    url = Column(String, primary_key=True)
    datetime = Column(DateTime)

children2 = relationship("ProjectFree", secondary=association_table, back_populates='parents2', cascade="all, delete")  # Many-to-many relationship

class ProjectFree(Base):
    __tablename__ = "project_freelancer"

    url = Column(String, primary_key=True)
    freel_url = Column(String, primary_key=True)
    update = Column(DateTime)

parents2 = relationship("Project", secondary=association_table, back_populates="children2", cascade="all, delete")

填充数据库时出现以下错误消息：

ERROR [21-11-18 09:58:47] scrapy.core.scraper _itemproc_finished :249 Error processing {'added': datetime.datetime(2021, 11, 18, 9, 58, 47, 654089),
 'freel_bidtext': 'Hi,\n'
                  '\n'
                  'I hope all is well with you.\n'
                  '\n'
                  'I have read the job description and finds it a perfect '
                  'match for me as I have extensive hands-on experience in '
                  'React JS/Vue JS development.\n'
                  '\n'
                  'I have developed a lot of websites and sto',
 'freel_country': 'Pakistan',
 'freel_deadline': 'in 7 days',
 'freel_earnings': '0.0',
 'freel_name': 'abdulhaseebbasit',
 'freel_price': '0 USD',
 'freel_ranking': 3,
 'freel_rating': '0.0',
 'freel_reviews': '0',
 'freel_url': 'https://www.freelancer.com/u/abdulhaseebbasit',
 'update': datetime.datetime(1900, 1, 1, 0, 0),
 'url': 'https://www.freelancer.com/projects/javascript/looking-for-react-developer-32135012/?ngsw-bypass=&w=f'}
Traceback (most recent call last):
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\engine\base.py", line 1802, in _execute_context
    self.dialect.do_execute(
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\engine\default.py", line 719, in do_execute
    cursor.execute(statement, parameters)
sqlite3.IntegrityError: UNIQUE constraint failed: association.projects_url

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\twisted\internet\defer.py", line 858, in _runCallbacks
    current.result = callback(  # type: ignore[misc]
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\scrapy\utils\defer.py", line 150, in f
    return deferred_from_coro(coro_f(*coro_args, **coro_kwargs))
  File "C:\Users\myuser\PycharmProjects\crawlerDiss\diss\diss\pipelines.py", line 42, in process_item
    return self.handle_ProjectFreelancer(item, spider)
  File "C:\Users\myuser\PycharmProjects\crawlerDiss\diss\diss\pipelines.py", line 160, in handle_ProjectFreelancer
    session.commit()
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\orm\session.py", line 1428, in commit
    self._transaction.commit(_to_root=self.future)
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\orm\session.py", line 829, in commit
    self._prepare_impl()
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\orm\session.py", line 808, in _prepare_impl
    self.session.flush()
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\orm\session.py", line 3345, in flush
    self._flush(objects)
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\orm\session.py", line 3485, in _flush
    transaction.rollback(_capture_exception=True)
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\util\langhelpers.py", line 70, in __exit__
    compat.raise_(
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\util\compat.py", line 207, in raise_
    raise exception
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\orm\session.py", line 3445, in _flush
    flush_context.execute()
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\orm\unitofwork.py", line 456, in execute
    rec.execute(self)
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\orm\unitofwork.py", line 579, in execute
    self.dependency_processor.process_saves(uow, states)
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\orm\dependency.py", line 1182, in process_saves
    self._run_crud(
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\orm\dependency.py", line 1245, in _run_crud
    connection.execute(statement, secondary_insert)
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\engine\base.py", line 1289, in execute
    return meth(self, multiparams, params, _EMPTY_EXECUTION_OPTS)
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\sql\elements.py", line 325, in _execute_on_connection
    return connection._execute_clauseelement(
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\engine\base.py", line 1481, in _execute_clauseelement
    ret = self._execute_context(
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\engine\base.py", line 1845, in _execute_context
    self._handle_dbapi_exception(
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\engine\base.py", line 2026, in _handle_dbapi_exception
    util.raise_(
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\util\compat.py", line 207, in raise_
    raise exception
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\engine\base.py", line 1802, in _execute_context
    self.dialect.do_execute(
  File "c:\users\myuser\pycharmprojects\crawlerdiss\venv\lib\site-packages\sqlalchemy\engine\default.py", line 719, in do_execute
    cursor.execute(statement, parameters)
sqlalchemy.exc.IntegrityError: (sqlite3.IntegrityError) UNIQUE constraint failed: association.projects_url
[SQL: INSERT INTO association (projects_url, project_freelancer_url, project_freelancer_freel_url) VALUES (?, ?, ?)]
[parameters: ('https://www.freelancer.com/projects/javascript/looking-for-react-developer-32135012/?ngsw-bypass=&w=f', 'https://www.freelancer.com/projects/javascript/looking-for-react-developer-32135012/?ngsw-bypass=&w=f', 'https://www.freelancer.com/u/abdulhaseebbasit')]
(Background on this error at: https://sqlalche.me/e/14/gkpj)

在我看到的 db-browser 中，只有唯一的组合被填充到关联中 table。因此，对于已经在协会 table 中的项目，与不同的自由职业者发生错误。你知道我必须改变什么吗？我应该在任何地方更改独特的行为吗？

Answer 1

我终于找到了解决方案，而且非常简单（这种情况经常发生）。在关联 table 中，我必须为每个外键添加 , primary_key = True。这是最后的 association_table:

association_table = Table('association', Base.metadata,
                          Column('projects_url', ForeignKey('projects.url', ondelete="CASCADE"), primary_key=True),
                          Column('project_freelancer_url', primary_key = True),
                          Column('project_freelancer_freel_url', primary_key = True),
                          ForeignKeyConstraint(
                              ('project_freelancer_url', 'project_freelancer_freel_url'),
                              ('project_freelancer.url', 'project_freelancer.freel_url')),
                          )

我通过阅读文档提示想到了这个想法 here。

SQLAlchemy 多对多 UNIQUE 约束关联失败 table

SQLAlchemy many-to-many UNIQUE constraint failed association table

many-to-many

sqlalchemy

associations

unique-constraint