在这种情况下如何正确使用ndb KeyProperty？ [英] How do I use ndb KeyProperty properly in this situation?

问题描述

我有两个模型：

pre $ class User（ndb.Model）：
email = ndb.StringProperty required = True）
name = ndb.StringProperty（required = True）
$ b $ class Post（ndb.Model）：
created = ndb.DateTimeProperty（auto_now_add = True）
message = ndb.TextProperty（required = True）
user = ndb.KeyProperty（kind = User）


如果我想循环Post模型中的某些帖子。我如何访问用户模型中的名称字段？例如：

 对于帖子中的帖子：
 print post.message 
 print post.user.name 
  

所以我猜最后一行是不正确的。我试图搜索，无法弄清楚。并补充一点。有没有办法在Jinja2模板中访问这些信息？

然后最后，我是否正在讨论这个错误？假设有50个职位。我有1个查询来获得这50个职位。访问用户模型上的名称字段将成为每次循环的附加查询？那么51查询如果是这样，是不是更好地使用KeyProperty，只是存储每个职位的用户数据（即使我有更多的数据，如头像，user_id等）？

解决方案

如果我没有记错， KeyProperty 会返回一个 ndb.Key 。一旦你有了密钥，很容易获得模型实例（ key.get（））。所以，在你的例子中，你会：

pre $ print post.user.get（）。

$ b



b


  {在帖子中的帖子％} 
 {{post.message}} 
 {{post.user.get（）。名称}} 
 {％endfor％} 
  

是的，这将与数据存储一旦你有每个关键。如果你愿意的话，你可以把它分成一个数据存储交互：



  keys = [p.user ] 
 users = ndb.get_multi（keys）
 user_posts = zip（users，posts）
  


$ b $然后在你的jinja模板中：



  {％user，post_user_posts％} 
 { {post.message}} 
 {{user.name}} 
 {％endfor％} 
  




I have two models:

class User(ndb.Model):
    email = ndb.StringProperty(required=True)
    name = ndb.StringProperty(required=True)

class Post(ndb.Model):
    created = ndb.DateTimeProperty(auto_now_add=True)
    message = ndb.TextProperty(required=True)
    user = ndb.KeyProperty(kind=User)

If I want to loop through some posts in the Post model. How I would access the 'name' field in the User model? For example:

for post in posts:
    print post.message
    print post.user.name

So I'm guessing the last line isn't correct. I tried searching and couldn't figure it out. And to add to that. Is there a way to access that info in a Jinja2 template?

And then finally, am I going about this wrong? Let's say there are 50 posts. And I have 1 query to get those 50 posts. Is accessing the 'name' field on the User model going to be an additional query for each time it loops? So 51 queries?? If so, is it better to not use KeyProperty and just store the User data with each post (even if I have more data like avatar, user_id, etc)?

解决方案

If I recall correctly, a KeyProperty will return you a ndb.Key. Once you have the key, it is easy to get the model instance (key.get()). So, in your example, you would:

print post.user.get().name

As far as accessing it in a jinja template -- Sure, it'd just be something like:

{% for post in posts %} 
{{ post.message }}
{{ post.user.get().name }}
{% endfor %}

And yes, this will interact with the datastore once for each key you have. If you'd rather, you can factor it out into one datastore interaction:

keys = [p.user for p in posts]
users = ndb.get_multi(keys)
user_posts = zip(users, posts)

And then in your jinja template:

{% for user, post in user_posts %}
{{ post.message }}
{{ user.name }}
{% endfor %}

这篇关于在这种情况下如何正确使用ndb KeyProperty？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！