Jinja2 模板如果条件不能正常工作

Question

我在 complete.html 的 Jinja2 模板中有一个 if 语句，但无论 if 条件是真还是假，它都不是运行正确的代码。

我调用重定向 url 到另一个视图函数，该函数随后呈现它，携带确定 if 循环条件的变量。我打印出条件并且它是正确的，但是 if-loop 没有运行正确的代码。我是否遗漏了导致 if 语句无法正常工作的内容。

我的代码：

view.py

@app.route('/', methods=['GET', 'POST'])
def home():
    form = CourseForm()

    if form.validate_on_submit():
        course_name = form.cname.data.upper()
        course_id = form.cid.data
        course_sec = form.sec.data.upper()
        email = form.email.data.lower()
        reserved = form.reserved.data

        result = checkCourse(course_name, course_id, course_sec)
        if result is not None:
            flash('Unable to find course')
        else:
            known = False
            course = Course.query.filter_by(cname=course_name, cid=course_id, sec=course_sec).first()
            if course is None:
                course = Course(cname=course_name, cid=course_id, sec=course_sec)
                db.session.add(course)
                db.session.flush()
                user = User(email=email, course_id=course.id, reserved=reserved)
                db.session.add(user)
            else:
                ckey = course.id
                result = checkUser(email, ckey, reserved)
                if result != None:
                    known = True
                else:
                    user = User(email=email, course_id=ckey, reserved=reserved)
                    db.session.add(user)
            db.session.commit()
            return redirect(url_for('complete', known=known))
    return render_template('home.html', form=form)

@app.route('/complete')
def complete():
    known = request.args.get('known', type=string)
    app.logger.debug(known)
    return render_template('complete.html', known=known)

模板：

base.html

{% extends "bootstrap/base.html" %}

{% block title %}UBC Course Alert{% endblock %}

{% block styles %}
{{super()}}
<link rel="stylesheet"
      href="{{url_for('.static', filename='home.css')}}">
{% endblock %}

{% block content %}
<div class="jumbotron">
    <div class="container">
        {% block page_content %}{% endblock %}
    </div>
</div>
{% endblock %}

complete.html

{% extends "base.html" %}
{% import "bootstrap/wtf.html" as wtf %}

{% block page_content %}

<p>
{% if known %}
  You already added this course. You'll receive a email as soon as there's space :)
{% else %}
  Thanks for registering your course, you'll receive a email as soon as there's space!
{% endif %}
</p>

{% endblock %}

Answer 1

您将变量 known 转换为字符串；它将包含字符串值 'True' 或 'False'。这些是 而不是 布尔值，而是 4 或 5 个字符长的字符串。然后两个字符串都被视为真值，因为它们是非空的。

您要么必须将字符串转换为布尔值，要么保留 known 值空以指示假值。

转换回布尔值非常简单：

known = request.args.get('known', type=string) == 'True'

如果为 false 使用空值，则如下所示：

return redirect(url_for('complete', known='1' if known else ''))

和

known = request.args.get('known', default='', type=bool)

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