如何解决SQLAlchemy ORM 多重多对多关系
我正在尝试制作电影数据库,并且我想要表:movies
、groups
(tags)、genres
和 directors
。我想要 groups
类中的 genres
、directors
和 Movie
列表以及每个类中的 movies
列表。
例如:
Movie:
file: str
id: str
title: str
etc: str
groups: list of Group
genres: list of Genre
directors: list of Director
Group:
group: str
movies: list of Movies with this Group
Genre:
genre: str
movies: list of Movies with this Genre
etc...
from sqlalchemy import Column,String,Integer,Float,ForeignKey,create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker,relationship
Base = declarative_base()
class Movie(Base):
__tablename__ = 'movies'
file = Column(String)
id = Column(String,primary_key=True)
title = Column(String)
year = Column(String)
runtime = Column(Integer)
rating = Column(Float)
group_name = Column(String,ForeignKey("groups.group"))
groups = relationship("Group",back_populates="movies")
genre_name = Column(String,ForeignKey("genres.genre"))
genres = relationship("Genre",back_populates="movies")
director_name = Column(String,ForeignKey("directors.name"))
directors = relationship("Director",back_populates="movies")
@classmethod
def from_dict(cls,info_dict: dict):
info_dict = {key: val for key,val in info_dict.items() if key in vars(cls)}
return cls(**info_dict)
class Group(Base):
__tablename__ = "groups"
group = Column(String,primary_key=True)
movies = relationship("Movie",back_populates="groups")
def __str__(self):
return self.group
def __repr__(self):
return f"<{self.__class__.__qualname__}(name={self.group})>"
def __eq__(self,other):
if other.__class__ == self.__class__:
return self.group == other.group
elif isinstance(other,str):
return self.group == other
return False
class Genre(Base):
__tablename__ = "genres"
genre = Column(String,back_populates="genres")
def __str__(self):
return self.genre
def __repr__(self):
return f"<{self.__class__.__qualname__}(name={self.genre})>"
class Director(Base):
__tablename__ = "directors"
name = Column(String,back_populates="directors")
def __str__(self):
return self.name
def __repr__(self):
return f"<{self.__class__.__qualname__}(name={self.name})>"
if __name__ == '__main__':
engine = create_engine(r"sqlite:///C:\path\to\movies.db")
session = sessionmaker(bind=engine)()
Base.Metadata.drop_all(engine)
Base.Metadata.create_all(engine)
info_dict = {
"file": "","id": "tt0848228","title": "The Avengers","year": "2012","runtime": 143,"rating": 8.0,"groups": [Group(group='marvel')],"directors": [Director(name="Joss Whedon")]
}
movie = Movie.from_dict(info_dict)
但是当我运行它时,我得到这个错误:
Traceback (most recent call last):
File "C:/tools/movie_db/test.py",line 108,in <module>
movie = Movie.from_dict(info_dict)
File "C:/tools/movie_db/test.py",line 44,in from_dict
return cls(**info_dict)
File "<string>",line 4,in __init__
File "C:\Users\Scott\.virtualenvs\movie_db-IqSCrsAm\lib\site-packages\sqlalchemy\orm\state.py",line 437,in _initialize_instance
manager.dispatch.init_failure(self,args,kwargs)
File "C:\Users\Scott\.virtualenvs\movie_db-IqSCrsAm\lib\site-packages\sqlalchemy\util\langhelpers.py",line 70,in __exit__
compat.raise_(
File "C:\Users\Scott\.virtualenvs\movie_db-IqSCrsAm\lib\site-packages\sqlalchemy\util\compat.py",line 198,in raise_
raise exception
File "C:\Users\Scott\.virtualenvs\movie_db-IqSCrsAm\lib\site-packages\sqlalchemy\orm\state.py",line 434,in _initialize_instance
return manager.original_init(*mixed[1:],**kwargs)
File "C:\Users\Scott\.virtualenvs\movie_db-IqSCrsAm\lib\site-packages\sqlalchemy\orm\decl_base.py",line 1132,in _declarative_constructor
setattr(self,k,kwargs[k])
File "C:\Users\Scott\.virtualenvs\media_organizer-IqSCrsAm\lib\site-packages\sqlalchemy\orm\attributes.py",line 431,in __set__
self.impl.set(
File "C:\Users\Scott\.virtualenvs\movie_db-IqSCrsAm\lib\site-packages\sqlalchemy\orm\attributes.py",line 1192,in set
value = self.fire_replace_event(state,dict_,value,old,initiator)
File "C:\Users\Scott\.virtualenvs\movie_db-IqSCrsAm\lib\site-packages\sqlalchemy\orm\attributes.py",line 1214,in fire_replace_event
value = fn(
File "C:\Users\Scott\.virtualenvs\movie_db-IqSCrsAm\lib\site-packages\sqlalchemy\orm\attributes.py",line 1643,in emit_backref_from_scalar_set_event
instance_state(child),AttributeError: 'list' object has no attribute '_sa_instance_state'
总的来说,我对 sqlAlchemy 和数据库非常陌生,所以我不确定我做错了什么。我知道 Group
的列表是导致问题的原因,但我什至不确定这些关系是否正确完成。建立像我想要的那种关系的正确方法是什么。感谢您的帮助。
解决方法
关键问题似乎是您的代码没有正确反映关系。 您需要(多次)是一个 Many to Many relationship,它需要一个关联表。
下面的代码说明了电影/组关系需要更改的内容,您可以对其他多对多关系重复相同的更改:
# define secondary table
user_group_table = Table(
"movies_groups",Base.metadata,Column("movie_id",ForeignKey("movies.id"),primary_key=True),Column("group_group",ForeignKey("groups.group"),)
...
# changes to the Movies model:
class Movie(Base):
__tablename__ = 'movies'
...
# REMOVE below row
# group_name = Column(String,ForeignKey("groups.group"))
# CHANGE below as shown
groups = relationship("Group",back_populates="movies",secondary=user_group_table)
...
# changes to the Group model:
class Group(Base):
__tablename__ = 'groups'
...
# CHANGE below as shown
movies = relationship("Movie",back_populates="groups",secondary=user_group_table)
...
现在下面应该可以工作了:
info_dict = {
"file": "","id": "tt0848228","title": "The Avengers","year": "2012","runtime": 143,"rating": 8.0,"groups": [Group(group='marvel'),Group(group='no-fun')],# commented out for now: "directors": [Director(name="Joss Whedon")]
}
movie = Movie.from_dict(info_dict)
session.add(movie)
session.commit()
...
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