python - NDB写入是如何计算的？

Question

如果我第二次向数据存储添加相同的数据，是否需要额外的写入操作？

例如，我有以下类(class):

class Song(ndb.Model):
    artist = ndb.StringProperty(required=True, indexed=True)
    title = ndb.StringProperty(required=True, indexed=False)

以及以下代码来添加新歌曲或更新现有值:

def add_song(artist, title):
    song_id = artist+ ' - ' + title
    record = Song.get_by_id(song_id)
    if not record:
        record = Song(id=song_id)
    record.artist = artist
    record.title = title
    record.put()

它会有效地工作吗？ IE。不会写艺术家和标题值，如果它们已经存在并且相同？或者，我应该像下面这样优化代码:

def add_song(artist, title):
    song_id = artist+ ' - ' + title
    record = Song.get_by_id(song_id)
    if not record:
        record = Song(id=song_id)
    if record.artist != artist: # new line!
        record.artist = artist
    if record.title != title: # new line!
        record.title = title
    if record.artist != artist or record.title != title: # new line!
        record.put()

这两个代码在调用时会生成相同数量的写入操作吗:

add_song('Artist Name', 'Song Title')
add_song('Artist Name', 'Song Title') # same artist, same title - second addition

或

add_song('Artist Name', 'Song Title')
add_song('Artist Name', 'New Song Title') # same artist, new title - second addition

？

Answer 1

是的，你应该优化——你只是做错了。

具体来说，您正在检查if record.artist !=artist &c) 之后您的代码段

if record.artist != artist: # new line!
    record.artist = artist

这当然可以确保 != 条件不会持续存在。因此，您永远不会达到可以调用 .put() 的条件。

尝试类似的事情:

def add_song(artist, title):
    song_id = artist+ ' - ' + title
    record = Song.get_by_id(song_id)
    if record:
        if record.artist != artist or record.title != title: # new line!
            record.artist = artist
            record.title = title
            is_new = True
        else:
            is_new = False
    else:
        record = Song(id=song_id, artist=artist, title=title)
        is_new = True
    if is_new:
         record.put()