Jinja2返回"None"(无). Google App Engine模型的字符串 [英] Jinja2 returns "None" string for Google App Engine models

问题描述

Google App Engine模型，例如:

Google App Engine models, likeso:

from google.appengine.ext.db import Model

class M(Model):
    name = db.StringProperty()

然后在从Django视图调用的Jinja2模板中，以M的in实例作为m传递:

Then in a Jinja2 template called from a Django view with an in instance of M passed in as m:

The name of this M is {{ m.name }}.

在未设置name的情况下初始化m时，将打印以下内容:

When m is initialized without name being set, the following is printed:

此M的名称为无".

The name of this M is None.

期望和期望的输出(以及使用Django模板时的输出)将是/是:

The preferable and expected output (and the output when using Django templates) would be/is:

这个M的名字是.

The name of this M is .

您知道为什么会这样吗，以及如何获得首选&预期产量?

Do you know why this is happening, and how to get the preferred & expected output?

推荐答案

您可能还想考虑使用Jinja2的或" ...

You might also want to consider using Jinja2's "or"...

The name of this M is {{ m.name or ''}}.

如果为bool(m.name) == False，则将显示The name of this M is .

如果m.name == False并希望将其显示为字符串"False"，则可以使用Jinja2的默认"过滤器:

If m.name == False and you want to display it as the string "False", you can use Jinja2's "default" filter:

The name of this M is {{ m.name|default('') }}

如果为m.name is None，则将显示The name of this M is .

如果为m.name == False，则将显示The name of this M is False.

如果您想使用默认过滤器，并且仍将评估为False的任何内容显示为定义的默认值，请添加一个额外的参数:

If you want to use the default filter and still have anything evaluating to False shown as your defined default value, add an extra param:

The name of this M is {{ m.name|default('', true) }}

这应该与{{ m.name or '' }}具有完全相同的效果.

This should have the exact same effect as {{ m.name or '' }}.

您可以在 Jinja2的内置过滤器参考

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