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使用 query 和 get 获取行

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使用 query 和 get 获取行 是 CoddyKit 上的免费 Flask Academy 课时。这是第 1 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。

Reading Starts With query

Every read from your database begins with the model's query attribute. It is your gateway to fetching rows as Python objects. 🔎

rows = User.query

Grab Everything with all

Call all() on a query to load every matching row into a plain Python list you can loop over.

users = User.query.all()
for u in users:
    print(u.name)

Just One With first

Use first() when you want a single row. It returns the first match, or None if the table has nothing to give.

user = User.query.first()

Fetch by Primary Key

When you know the id, get() is the fastest path. Hand it the primary key and it returns that exact row.

user = User.query.get(7)

get Returns None When Missing

If no row has that id, get() quietly returns None instead of raising. Always check before you use the result.

user = User.query.get(999)
if user is None:
    print("not found")

404 the Easy Way

In a view, get_or_404() fetches by id and auto-aborts with a 404 page when the row is absent. No manual check needed.

user = User.query.get_or_404(7)

first_or_404 for Filtered Reads

Pair first_or_404() with a filter to grab one match or raise a clean 404 when nothing fits.

u = User.query.filter_by(email=e).first_or_404()

Count Without Loading Rows

Need a tally, not the data? count() asks the database for the number directly, so you never pull full rows into memory.

total = User.query.count()

Queries Are Lazy

Building a query does not touch the database yet. The SQL only runs when you call a method like all, first, or get.

q = User.query
results = q.all()

Each Row Is an Object

Results come back as real model instances, so you read columns as ordinary attributes like user.name and user.email.

user = User.query.first()
print(user.email)

Pick the Right Fetch

Use get for a known id, first for one of many, and all for the whole set. Choosing well keeps reads clear and fast.

Quick Check

You know a record's primary key. Which call fetches it most directly?

Recap: Fetching Rows

You now read data with query: all for lists, first for one, get by id, and the or_404 helpers for clean views. Nice work! 🎉

常见问题解答

「使用 query 和 get 获取行」课时是免费的吗？

是的 — 「使用 query 和 get 获取行」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 Flask Academy 课程的其余内容，请升级到 CoddyKit PRO。 Flask Academy 课程共包含 4 节课。

「使用 query 和 get 获取行」这节课中我会学到什么？

获取全部记录、单条记录或按主键获取记录你通过在浏览器中直接运行的动手代码来练习 Flask Academy，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 Flask Academy 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Flask Academy 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。这是第 1 节课，共 4 节。

「使用 query 和 get 获取行」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。

我能在这节 Flask Academy 课中编写并运行代码吗？

能。每节 Flask Academy 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

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