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validate_on_submit 与 CSRF 令牌

处理有效的提交，并阻止伪造请求

第 3 / 4 课13 个步骤

validate_on_submit 与 CSRF 令牌 是 CoddyKit 上的免费 Flask Academy 课时。这是第 3 节课，共 4 节。你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。这是 Flask Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Flask Academy 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

The Golden Method

Flask-WTF gives you one method that checks everything at once. validate_on_submit is the heart of safely processing any form. 🔑

What It Actually Checks

validate_on_submit returns True only when the request is a POST and every validator passes. One call covers both conditions.

if form.validate_on_submit():
    pass  # safe to use the data

The Standard View Pattern

This shape repeats in every Flask app: build the form, branch on validate_on_submit, then fall through to render the page.

form = LoginForm()
if form.validate_on_submit():
    return redirect('/home')
return render_template('login.html', form=form)

Submitted vs Valid

Do not confuse the two. is_submitted only checks the method, while validate_on_submit also confirms the data passed every rule.

form.is_submitted()        # POST? 
form.validate_on_submit()  # POST and valid?

Why CSRF Matters

A CSRF attack tricks a logged-in user into submitting a form they never meant to. Tokens prove the request came from your own page.

SECRET_KEY Is Required

CSRF tokens are signed, so Flask needs a SECRET_KEY. Without it, validation fails and Flask-WTF refuses to protect the form.

app.config['SECRET_KEY'] = 'change-me-in-production'

The Token in the Page

That call to hidden_tag embeds the signed token as a hidden input. The browser sends it back with every submission.

{{ form.hidden_tag() }}

Validation Compares Tokens

On submit, Flask-WTF compares the posted token against the session. A missing or stale token makes validate_on_submit return False.

if not form.validate_on_submit():
    pass  # bad token or failed rule

Inspect Why It Failed

When validation fails, look at form.errors. It maps each field name to the list of messages explaining the problem.

if not form.validate_on_submit():
    print(form.errors)

Process Then Redirect

After a successful submit, finish with a redirect. That follows the PRG pattern and stops a refresh from posting twice.

if form.validate_on_submit():
    save(form.data)
    return redirect('/done')

Never Disable CSRF Blindly

You can turn off CSRF for APIs, but never for browser forms. Keeping protection on is what makes Flask-WTF worth using.

Quick Check

When does form.validate_on_submit() return True?

在交互式课程中回答

Recap

You leaned on validate_on_submit for the method-plus-rules check, set a SECRET_KEY for signed CSRF tokens, and redirected after success. 🛡️

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常见问题解答

「validate_on_submit 与 CSRF 令牌」课时是免费的吗？

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「validate_on_submit 与 CSRF 令牌」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

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