我正在尝试使用具有多对多关系的SQLAlchemy来设置电影数据库。我有两个表，'movie'和'actor'，以及一个关联表'movie_actor'。我希望能够将新电影添加到电影表中，但如果这部新电影中的一些演员已经在演员表中，我想防止在演员表中复制它们，同时仍然添加movie_id和actor_id是关联表。这是我的表格设置：
from sqlalchemy import Table, Column, Integer, String, ForeignKey, create_engine, and_, or_
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import backref, mapper, relationship, Session
Base = declarative_base()
formats = {'1': 'DVD', '2': 'Blu-ray', '3': 'Digital', '4': 'VHS'}
###########################################################################################
class Movie(Base):
"""Movie Class"""
__tablename__ = "movie"
movie_id = Column(Integer, primary_key=True)
title = Column(String(20), nullable=False, unique=True)
year = Column(Integer, nullable=False)
format = Column(String, nullable=False)
movie_actor = relationship("MovieActor", cascade="all, delete-orphan", backref="movie")
def __init__(self, title, year, format):
self.title = title
self.year = year
self.format = format
def __repr__(self):
return "%s %s" % (self.movie_id, self.title)
###########################################################################################
class Actor(Base):
"""Actor Class"""
__tablename__ = "actor"
actor_id = Column(Integer, primary_key=True)
full_name = Column(String(30), nullable=False, unique=True)
def __init__(self, full_name):
self.full_name = full_name
def __repr__(self):
return "%s %s" % (self.actor_id, self.full_name)
###########################################################################################
class MovieActor(Base):
"""MovieActor Association Class"""
__tablename__ = "movieactor"
movie_id = Column(Integer, ForeignKey('movie.movie_id'), primary_key=True)
actor_id = Column(Integer, ForeignKey('actor.actor_id'), primary_key=True)
def __init__(self, actor):
self.actor = actor
actor = relationship(Actor, lazy='joined')
def __repr__(self):
return "%s, %s" % (self.movie_id, self.actor_id)
这是一个将处理插入新条目并查询数据库的类：
###########################################################################################
class Database(object):
# A connection to the movie database is established upon instantiation.
def __init__(self):
engine = create_engine('sqlite:///bmdb.db')
Base.metadata.create_all(engine)
session = Session(engine)
self.session = session
# add_new method takes a dictionary of strings containing all the info for a new movie: "title, year, format, actors"
# and formats the strings, then adds them to the proper tables in the database
def add_new(self, new_movie):
#find out what formats exist
format = ""
for i in range(1,5):
try:
format += new_movie[formats[str(i)]]
format += ", "
except:
pass
format = format[:-1]
format = format[:-1]
# capitalize the first letter of each word in the movie title
title = " ".join(word[0].upper() + word[1:].lower() for word in new_movie['title'].split())
try:
movie = Movie(title, new_movie['year'], format)
# add the new movie to the session
self.session.add(movie)
# commit the new movie to the database
self.session.commit()
except:
print "Duplicate Movie"
self.session.rollback()
return
# parse the text in the actors entry
# take the incoming string of all actors in the movie and split it into a list of individual actors
actors = new_movie['actors'].split(", ")
for i in range(len(actors)):
# for each actor in the list, capitalize the first letter in their first and last names
actors[i] = " ".join(word[0].upper() + word[1:].lower() for word in actors[i].split())
# add each formatted actor name to the Actor table
actor = Actor(actors[i])
try:
# add the appropriate association between the movie and the actors to the MovieActor table
movie.movie_actor.append(MovieActor(actor))
# add the new actor and movieactor association to the session
self.session.add(movie)
self.session.commit()
except:
print "Duplicate Actor"
self.session.rollback()
正如我的代码现在所示，add_new（）方法中的try / except块可以防止将重复的actor添加到数据库，因为actor表中的'full_name'列设置为unique = True，但这也可以防止要添加到movie_actor关联表中的条目。
基本上我想知道的是如何添加电影，检查电影中的演员是否已经存在于actor表中，如果他们这样做，请不要将actor插入actor表中，而是他们在actor表中的现有actor_id，并在movie_actor关联表中创建适当的关联。
答案 0 :(得分：2)
您可能需要在self.session.begin_nested()区块中插入try:。
然后，如果由于重复键需要回滚，您仍然可以将actor添加到电影中：
from sqlalchemy.exc import IntegrityError # only catch the right exception!
# in for loop:
try:
session.begin_nested()
actor = Actor(actors[i])
except IntegrityError:
print "Duplicate Actor"
self.session.rollback() # subtransaction
actor = self.session.query(Actor).\
filter(Actor.name==actors[i]).first()
else:
self.session.commit() # subtransaction
# add the appropriate association between the movie and the actors to the MovieActor table
movie.movie_actor.append(MovieActor(actor))
# add the new actor and movieactor association to the session
self.session.add(movie)
self.session.commit()
编辑：当期待重复的密钥错误时，始终除了IntegrityError。