def fanout_to_followers(cls, tweet):
newsfeeds = [
NewsFeed(user=follower, tweet=tweet)
for follower in FriendshipService.get_followers(tweet.user)
]
newsfeeds.append(NewsFeed(user=tweet.user, tweet=tweet))
NewsFeed.objects.bulk_create(newsfeeds)
def fanout_to_followers(cls, tweet):
# 错误的方法
# 不可以将数据库操作放在 for 循环里面，效率会非常低
# for follower in FriendshipService.get_followers(tweet.user):
# NewsFeed.objects.create(
# user=follower,
# tweet=tweet,
# )
# 正确的方法：使用 bulk_create，会把 insert 语句合成一条
print(FriendshipService.get_followers(tweet.user))
newsfeeds = [
NewsFeed(user=follower, tweet=tweet)
for follower in FriendshipService.get_followers(tweet.user)
]
newsfeeds.append(NewsFeed(user=tweet.user, tweet=tweet))
NewsFeed.objects.bulk_create(newsfeeds)
def fanout_to_followers(cls, tweet):
newsfeeds = [
NewsFeed(user=follower, tweet=tweet)
for follower in FriendshipService.get_followers(tweet.user)
]
newsfeeds.append(NewsFeed(user=tweet.user, tweet=tweet))
NewsFeed.objects.bulk_create(newsfeeds)
# bulk create 不会触发 post_save 的 signal，所以需要手动 push 到 cache 里
for newsfeed in newsfeeds:
cls.push_newsfeed_to_cache(newsfeed)
def fan_out_to_followers(cls, tweet):
followers = FriendshipService.get_followers(tweet.user)
newsfeeds = [
NewsFeed(tweet=tweet, user=follower, created_at=tweet.created_at)
for follower in followers
]
#should be able to see own posts
newsfeeds.append(
NewsFeed(tweet=tweet, user=tweet.user,
created_at=tweet.created_at))
NewsFeed.objects.bulk_create(newsfeeds)
def fanout_to_followers(cls, tweet):
# Wrong way to do the creation:
# cannot put database op in a for loop, very inefficient
# for follower in FriendshipService.get_followers(tweet.user):
# NewsFeed.objects.create(
# user=follower,
# tweet=tweet,
# )
# 正确的方法：使用 bulk_create，会把 insert 语句合成一条
# Right way: use bulk_create, which combines all insert SQLs into one
# line
newsfeeds = [
# Request for update will not be made until .save()
NewsFeed(user=follower, tweet=tweet)
for follower in FriendshipService.get_followers(tweet.user)
]
newsfeeds.append(NewsFeed(user=tweet.user, tweet=tweet))
NewsFeed.objects.bulk_create(newsfeeds) # create newsfeeds in a batch
def fanout_to_followers(cls, tweet):
# 错误的方法
# 在production 是不允许for + query的 效率很低
# 原因是 web server和 db通常不在一台机器上 多次查询会产生大量延迟 (round trip多 -- 用户信息的验证)
# for follower in FriendshipService.get_followers(tweet.user):
# NewsFeed.objects.create(
# user=follower,
# tweet=tweet,
# )
# 正确的方法： 使用bulk_create, 会把insert语句合成一条
newsfeeds = [
NewsFeed(user=follower, tweet=tweet) # 由于此处没有.save 所以不会产生数据库存储请求操作
for follower in FriendshipService.get_followers(tweet.user)
]
# 由于用户自己不是自己的follower
# 此处是把用户本身也加入到follower中使得自己也可以看到自己的newsfeed
newsfeeds.append(NewsFeed(user=tweet.user, tweet=tweet))
NewsFeed.objects.bulk_create(newsfeeds)
