使用sqlite、sqlalchemy和python在数据库中重复插入的问题

Question

我正在学习Python，通过网上的资源和这个网站上的朋友们的帮助，我渐渐掌握了它。在我的第一个脚本中，我正在解析Twitter的RSS源，并把结果插入到数据库里，但还有一个问题我解决不了。也就是说，有重复的条目被插入到其中一个表里。

先说一下背景，我最开始在HalOtis.com找到了一个基础脚本，用来下载RSS源，然后我对它做了几处修改：1）修改了以适应Twitter RSS源的一些特殊情况（它没有分开内容、标题、网址等）；2）增加了“标签”的表，以及用于多对多关系的表（entry_tag表）；3）把表的设置改成了sqlalchemy；4）做了一些临时的修改，以解决出现的奇怪的unicode问题。因此，代码在某些地方看起来很乱，但这是一个很好的学习经历，现在它能正常工作了——除了在“entries”表中不断插入重复数据。

因为我不确定什么对大家最有帮助，所以我把整个代码粘贴在下面，并在几个地方加了一些注释，指出我认为最重要的部分。

我非常感谢任何帮助。谢谢！

编辑：有人建议我提供数据库的结构。我以前从没做过这个，所以如果我做的不对，请多包涵。我正在设置四个表：

RSSFeeds，包含Twitter RSS源的列表
RSSEntries，包含从每个源下载的单个条目的列表（解析后），有内容、标签、日期、网址等列
Tags，包含在单个条目（推文）中找到的所有标签的列表
entry_tag，包含允许我将标签映射到条目的列。

简而言之，下面的脚本从RSS Feeds表中获取五个测试RSS源，下载每个源的20个最新条目/推文，解析这些条目，并把信息放入RSS Entries、Tags和entry_tag表中。

#!/usr/local/bin/python

import sqlite3
import threading
import time
import Queue
from time import strftime
import re       
from string import split 
import feedparser 
from django.utils.encoding import smart_str, smart_unicode      
from sqlalchemy import schema, types, ForeignKey, select, orm
from sqlalchemy import create_engine

engine = create_engine('sqlite:///test98.sqlite', echo=True)
metadata = schema.MetaData(engine)   
metadata.bind = engine

def now():
    return datetime.datetime.now()


#set up four tables, with many-to-many relationship
RSSFeeds = schema.Table('feeds', metadata,
    schema.Column('id', types.Integer, 
        schema.Sequence('feeds_seq_id', optional=True), primary_key=True),
    schema.Column('url', types.VARCHAR(1000), default=u''),
)


RSSEntries = schema.Table('entries', metadata,
    schema.Column('id', types.Integer, 
        schema.Sequence('entries_seq_id', optional=True), primary_key=True),
    schema.Column('feed_id', types.Integer, schema.ForeignKey('feeds.id')),
    schema.Column('short_url', types.VARCHAR(1000), default=u''),
    schema.Column('content', types.Text(), nullable=False),
    schema.Column('hashtags', types.Unicode(255)),
    schema.Column('date', types.String()),  
)


tag_table = schema.Table('tag', metadata,
    schema.Column('id', types.Integer,
       schema.Sequence('tag_seq_id', optional=True), primary_key=True),
    schema.Column('tagname', types.Unicode(20), nullable=False, unique=True),
)


entrytag_table = schema.Table('entrytag', metadata,
    schema.Column('id', types.Integer,
        schema.Sequence('entrytag_seq_id', optional=True), primary_key=True),
    schema.Column('entryid', types.Integer, schema.ForeignKey('entries.id')),
    schema.Column('tagid', types.Integer, schema.ForeignKey('tag.id')),
)


metadata.create_all(bind=engine, checkfirst=True)


# Insert test set of Twitter RSS feeds
stmt = RSSFeeds.insert()
stmt.execute(
    {'url': 'http://twitter.com/statuses/user_timeline/14908909.rss'},
    {'url': 'http://twitter.com/statuses/user_timeline/52903246.rss'},
    {'url': 'http://twitter.com/statuses/user_timeline/41902319.rss'},
    {'url': 'http://twitter.com/statuses/user_timeline/29950404.rss'},
    {'url': 'http://twitter.com/statuses/user_timeline/35699859.rss'},
)



#These 3 lines for threading process (see HalOtis.com for example) 
THREAD_LIMIT = 20
jobs = Queue.Queue(0)
rss_to_process = Queue.Queue(THREAD_LIMIT)


#connect to sqlite database and grab the 5 test RSS feeds
conn = engine.connect()
feeds = conn.execute('SELECT id, url FROM feeds').fetchall()

#This block contains all the parsing and DB insertion 
def store_feed_items(id, items):
    """ Takes a feed_id and a list of items and stores them in the DB """
    for entry in items:
        conn.execute('SELECT id from entries WHERE short_url=?', (entry.link,))
        #note: entry.summary contains entire feed entry for Twitter, 
                    #i.e., not separated into content, etc.
        s = unicode(entry.summary) 
        test = s.split()
        tinyurl2 = [i for i in test if i.startswith('http://')]
        hashtags2 = [i for i in s.split() if i.startswith('#')]
        content2 = ' '.join(i for i in s.split() if i not in tinyurl2+hashtags2)
        content = unicode(content2)
        tinyurl = unicode(tinyurl2)
        hashtags = unicode (hashtags2)
        print hashtags
        date = strftime("%Y-%m-%d %H:%M:%S",entry.updated_parsed)


        #Insert parsed feed data into entries table 
                    #THIS IS WHERE DUPLICATES OCCUR
        result = conn.execute(RSSEntries.insert(), {'feed_id': id, 'short_url': tinyurl,
            'content': content, 'hashtags': hashtags, 'date': date})
        entry_id = result.last_inserted_ids()[0]


        #Look up tag identifiers and create any that don't exist:
        tags = tag_table
        tag_id_query = select([tags.c.tagname, tags.c.id], tags.c.tagname.in_(hashtags2))
        tag_ids = dict(conn.execute(tag_id_query).fetchall())
        for tag in hashtags2:
            if tag not in tag_ids:
                result = conn.execute(tags.insert(), {'tagname': tag})
                tag_ids[tag] = result.last_inserted_ids()[0]

        #insert data into entrytag table 
        if hashtags2: conn.execute(entrytag_table.insert(),
            [{'entryid': entry_id, 'tagid': tag_ids[tag]} for tag in hashtags2])


#Rest of file completes the threading process     
def thread():
    while True:
        try:
            id, feed_url = jobs.get(False) # False = Don't wait
        except Queue.Empty:
            return

        entries = feedparser.parse(feed_url).entries
        rss_to_process.put((id, entries), True) # This will block if full

for info in feeds: # Queue them up
    jobs.put([info['id'], info['url']])

for n in xrange(THREAD_LIMIT):
    t = threading.Thread(target=thread)
    t.start()

while threading.activeCount() > 1 or not rss_to_process.empty():
    # That condition means we want to do this loop if there are threads
    # running OR there's stuff to process
    try:
        id, entries = rss_to_process.get(False, 1) # Wait for up to a second
    except Queue.Empty:
        continue

    store_feed_items(id, entries)

database sqlalchemy sqlite rss data parsing data insertion unique constraint many-to-many relationship

使用sqlite、sqlalchemy和python在数据库中重复插入的问题

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