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筛选、排序并限制结果

使用 filter_by、order_by 和分页

筛选、排序并限制结果 是 CoddyKit 上的免费 Flask Academy 课时。这是第 2 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。

Narrow Results with filter_by

Use filter_by() with keyword arguments to keep only rows that match a column exactly. It reads almost like English. 🎯

admins = User.query.filter_by(role="admin").all()

More Power with filter

When you need comparisons, reach for filter() and full column expressions instead of plain equality.

adults = User.query.filter(User.age >= 18).all()

Combine Conditions

Pass several expressions to filter() and they join with AND, so every condition must hold for a row to match.

q = User.query.filter(User.age >= 18, User.active == True)

OR Conditions

For an either-or match, wrap conditions in or_() so a row qualifies when any one of them is true.

from sqlalchemy import or_
q = User.query.filter(or_(User.age < 18, User.vip))

Sort with order_by

Use order_by() to sort results by a column. By default rows come back in ascending order.

users = User.query.order_by(User.name).all()

Newest First with desc

Wrap a column in desc() to flip the sort and put the largest or latest values at the top.

posts = Post.query.order_by(Post.created.desc()).all()

Cap the Count with limit

Add limit() to fetch only the first N rows. It keeps responses small and queries fast.

top = Post.query.order_by(Post.score.desc()).limit(5).all()

Skip Rows with offset

Use offset() to skip a number of rows before returning. Combined with limit, it gives you simple paging.

page2 = Post.query.limit(10).offset(10).all()

Real Pagination with paginate

Flask-SQLAlchemy bundles paging into paginate(), which returns items plus handy page metadata in one call.

p = Post.query.paginate(page=2, per_page=10)

Chain It All Together

Filter, order, and limit chain fluently, and nothing runs until you finish with all or first.

q = Post.query.filter_by(public=True).order_by(Post.id.desc()).limit(3)

Order Matters for Limits

Always pair limit() with order_by. Without a sort, which rows you get back is unpredictable.

Quick Check

You want the three highest-scoring posts. Which clause makes the score the top result?

Recap: Shaping Results

You can now filter, sort with order_by and desc, and trim output with limit, offset, and paginate. Powerful reads unlocked! 🚀

常见问题解答

「筛选、排序并限制结果」课时是免费的吗？

是的 — 「筛选、排序并限制结果」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。

「筛选、排序并限制结果」这节课中我会学到什么？

使用 filter_by、order_by 和分页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 2 节课，共 4 节。

「筛选、排序并限制结果」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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