Scrapy SQLalchemy外键未在SQLite中创建

Question

我尝试使用itemLoader运行Scrapy来收集所有数据并将它们放入SQLite3。我成功地收集了我想要的所有信息，但是我无法使用带有外键的back_populates在我的ThreadInfo和PostInfo表中生成外键。我确实试过使用back_ref，但它也不起作用。 我的剪贴画完成后，所有其他信息都被插入SQLite数据库

我的目标是让boardInfo、threadInfo、postInfo和authorInfo这四个表相互链接

• boardInfo将与threadInfo建立一对多关系
• threadInfo将与postInfo建立一对多关系
• authorInfo将与threadInfo和
  建立一对多关系 postInfo

我使用DB Browser for SQLite，发现外键的值是Null。 我尝试查询该值（threadInfo.boardInfos_id），结果显示None。我花了很多天试图解决这个问题，并通读了文档，但无法解决这个问题

如何在threadInfo和postInfo表中生成外键

感谢您的指导和评论

这是我的模特

from sqlalchemy import create_engine, Column, Table, ForeignKey, MetaData
from sqlalchemy import Integer, String, Date, DateTime, Float, Boolean, Text
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base
from scrapy.utils.project import get_project_settings

Base = declarative_base()

def db_connect():
    '''
    Performs database connection using database settings from settings.py.
    Returns sqlalchemy engine instance
    '''
    return create_engine(get_project_settings().get('CONNECTION_STRING'))

def create_table(engine):
    Base.metadata.create_all(engine)

class BoardInfo(Base): 
    __tablename__ = 'boardInfos'
    id = Column(Integer, primary_key=True)
    boardName = Column('boardName', String(100)) 
    threadInfosLink = relationship('ThreadInfo', back_populates='boardInfosLink') # One-to-Many with threadInfo

class ThreadInfo(Base):
    __tablename__ = 'threadInfos'
    id = Column(Integer, primary_key=True)
    threadTitle = Column('threadTitle', String())
    threadLink = Column('threadLink', String())
    threadAuthor = Column('threadAuthor', String())
    threadPost = Column('threadPost', Text())
    replyCount = Column('replyCount', Integer)
    readCount = Column('readCount', Integer)

    boardInfos_id = Column(Integer, ForeignKey('boardInfos.id')) # Many-to-One with boardInfo
    boardInfosLink = relationship('BoardInfo', back_populates='threadInfosLink') # Many-to-One with boardInfo

    postInfosLink = relationship('PostInfo', back_populates='threadInfosLink') # One-to-Many with postInfo
    
    authorInfos_id = Column(Integer, ForeignKey('authorInfos.id')) # Many-to-One with authorInfo
    authorInfosLink = relationship('AuthorInfo', back_populates='threadInfosLink') # Many-to-One with authorInfo

class PostInfo(Base):
    __tablename__ = 'postInfos'
    id = Column(Integer, primary_key=True)
    postOrder = Column('postOrder', Integer, nullable=True)
    postAuthor = Column('postAuthor', Text(), nullable=True)
    postContent = Column('postContent', Text(), nullable=True)
    postTimestamp = Column('postTimestamp', Text(), nullable=True)

    threadInfos_id = Column(Integer, ForeignKey('threadInfos.id')) # Many-to-One with threadInfo 
    threadInfosLink = relationship('ThreadInfo', back_populates='postInfosLink') # Many-to-One with threadInfo 
    
    authorInfos_id = Column(Integer, ForeignKey('authorInfos.id')) # Many-to-One with authorInfo
    authorInfosLink = relationship('AuthorInfo', back_populates='postInfosLink') # Many-to-One with authorInfo

class AuthorInfo(Base):
    __tablename__ = 'authorInfos'
    id = Column(Integer, primary_key=True)
    threadAuthor = Column('threadAuthor', String())

    postInfosLink = relationship('PostInfo', back_populates='authorInfosLink') # One-to-Many with postInfo
    threadInfosLink = relationship('ThreadInfo', back_populates='authorInfosLink') # One-to-Many with threadInfo

这是我的管道

from sqlalchemy import exists, event
from sqlalchemy.orm import sessionmaker
from scrapy.exceptions import DropItem
from .models import db_connect, create_table, BoardInfo, ThreadInfo, PostInfo, AuthorInfo
from sqlalchemy.engine import Engine
from sqlite3 import Connection as SQLite3Connection
import logging

@event.listens_for(Engine, "connect")
def _set_sqlite_pragma(dbapi_connection, connection_record):
    if isinstance(dbapi_connection, SQLite3Connection):
        cursor = dbapi_connection.cursor()
        cursor.execute("PRAGMA foreign_keys=ON;")
        # print("@@@@@@@ PRAGMA prog is running!! @@@@@@")
        cursor.close()

class DuplicatesPipeline(object):

    def __init__(self):
        '''
        Initializes database connection and sessionmaker.
        Creates tables.
        '''
        engine = db_connect()
        create_table(engine)
        self.Session = sessionmaker(bind=engine)
        logging.info('****DuplicatesPipeline: database connected****')

    def process_item(self, item, spider):

        session = self.Session()
        
        exist_threadLink = session.query(exists().where(ThreadInfo.threadLink == item['threadLink'])).scalar()
        exist_thread_replyCount = session.query(ThreadInfo.replyCount).filter_by(threadLink = item['threadLink']).scalar()
        if exist_threadLink is True: # threadLink is in DB
            if exist_thread_replyCount < item['replyCount']: # check if replyCount is more?
                return item
                session.close()
            else:
                raise DropItem('Duplicated item found and replyCount is not changed')
                session.close()
        else: # New threadLink to be added to BoardPipeline
            return item
            session.close()

class BoardPipeline(object):
    def __init__(self):
        '''
        Initializes database connection and sessionmaker
        Creates tables
        '''
        engine = db_connect()
        create_table(engine)
        self.Session = sessionmaker(bind=engine)

    def process_item(self, item, spider):
        '''
        Save scraped info in the database
        This method is called for every item pipeline component
        '''

        session = self.Session()

        # Input info to boardInfos
        boardInfo = BoardInfo()
        boardInfo.boardName = item['boardName']
        
        # Input info to threadInfos
        threadInfo = ThreadInfo()
        threadInfo.threadTitle = item['threadTitle']
        threadInfo.threadLink = item['threadLink']
        threadInfo.threadAuthor = item['threadAuthor']
        threadInfo.threadPost = item['threadPost']
        threadInfo.replyCount = item['replyCount']
        threadInfo.readCount = item['readCount']

        # Input info to postInfos
        # Due to info is in list, so we have to loop and add it.
        for num in range(len(item['postOrder'])):
            postInfoNum = 'postInfo' + str(num)
            postInfoNum = PostInfo()
            postInfoNum.postOrder = item['postOrder'][num]
            postInfoNum.postAuthor = item['postAuthor'][num]
            postInfoNum.postContent = item['postContent'][num]
            postInfoNum.postTimestamp = item['postTimestamp'][num]
            session.add(postInfoNum)
        
        # Input info to authorInfo
        authorInfo = AuthorInfo()
        authorInfo.threadAuthor = item['threadAuthor'] 

        # check whether the boardName exists
        exist_boardName = session.query(exists().where(BoardInfo.boardName == item['boardName'])).scalar()
        if exist_boardName is False:  # the current boardName does not exists
            session.add(boardInfo)

        # check whether the threadAuthor exists
        exist_threadAuthor = session.query(exists().where(AuthorInfo.threadAuthor == item['threadAuthor'])).scalar()
        if exist_threadAuthor is False:  # the current threadAuthor does not exists
            session.add(authorInfo)

        try:
            session.add(threadInfo)
            session.commit()

        except:
            session.rollback()
            raise

        finally:
            session.close()

        return item

Answer 1

根据我的另一个答案评论中的讨论，下面是我将如何合理化您的模型，使它们对我更有意义

注意:

1. 我已经删除了所有不必要的“信息”
2. 我已经从您的模型定义中删除了显式列名，并将依赖SQLAlchemy的能力根据我的属性名为我推断这些列名
3. 在“Post”对象中，我没有将属性命名为PostContent，这意味着内容与Post相关，因为这就是我们访问它的方式，而只是将属性称为“Post”
4. 我已经删除了所有“链接”术语，在我认为您需要引用相关对象集合的地方，我已经提供了该对象的复数属性作为关系
5. 我在Post模型中留下了一行供您删除。正如你所看到的，你不需要两次“作者”，一次作为相关对象，一次在帖子上，这违背了FKs的目的

通过这些更改，当您尝试从其他代码中使用这些模型时，很明显您需要在何处使用.append（），以及在何处只分配相关对象。对于给定的Board对象，您知道“threads”是一个仅基于属性名的集合，因此您将执行类似于b.threads.append(thread)

from sqlalchemy import create_engine, Column, Table, ForeignKey, MetaData
from sqlalchemy import Integer, String, Date, DateTime, Float, Boolean, Text
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base

class Board(Base): 
    __tablename__ = 'board'
    id = Column(Integer, primary_key=True)
    name = Column(String(100)) 
    threads = relationship(back_populates='board')

class Thread(Base):
    __tablename__ = 'thread'
    id = Column(Integer, primary_key=True)
    title = Column(String())
    link = Column(String())
    author = Column(String())
    post = Column(Text())
    reply_count = Column(Integer)
    read_count = Column(Integer)

    board_id = Column(Integer, ForeignKey('Board.id'))
    board = relationship('Board', back_populates='threads')

    posts = relationship('Post', back_populates='threads')
    
    author_id = Column(Integer, ForeignKey('Author.id'))
    author = relationship('Author', back_populates='threads')

class Post(Base):
    __tablename__ = 'post'
    id = Column(Integer, primary_key=True)
    order = Column(Integer, nullable=True)
    author = Column(Text(), nullable=True)    # remove this line and instead use the relationship below
    content = Column(Text(), nullable=True)
    timestamp = Column(Text(), nullable=True)

    thread_id = Column(Integer, ForeignKey('Thread.id'))
    thread = relationship('Thread', back_populates='posts')
    
    author_id = Column(Integer, ForeignKey('Author.id')) 
    author = relationship('Author', back_populates='posts')

class AuthorInfo(Base):
    __tablename__ = 'author'
    id = Column(Integer, primary_key=True)
    name = Column(String())

    posts = relationship('Post', back_populates='author') 
    threads = relationship('Thread', back_populates='author')

Answer 2

从我看到的代码中，我觉得您并不是在任何地方设置ThreadInfo.authorInfosLink或ThreadInfo.authorInfos_id（您的所有FK/关系也是如此）

对于要附加到ThreadInfo实例的相关对象，您需要创建它们，然后附加它们，如下所示：

        # Input info to authorInfo
        authorInfo = AuthorInfo()
        authorInfo.threadAuthor = item['threadAuthor'] 
        
        threadInfo.authorInfosLink = authorInfo

如果每个对象通过FK相关，则可能不希望将其session.add（）添加到每个对象中。您将希望：

1. 实例化一个BoardInfo对象bi
2. 然后实例化附加相关的ThreadInfo对象ti
3. 将您的文件附加到相关对象上，例如bi.threadInfosLink = ti
4. 在所有链接关系结束时，只需使用session.add(bi)将bi添加到会话中即可。所有相关对象都将通过它们的关系添加，FKs将是正确的