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values、values_list 与 count

提取轻量数据并进行聚合

values、values_list 与 count 是 CoddyKit 上的免费 Django Academy 课时。这是第 4 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 Django Academy 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 Django 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。

Why Go Lightweight

Full model objects carry every field. When you only need a column or two, lighter tools fetch less data and run faster.

values() Returns Dicts

Call values() and each row comes back as a dictionary instead of a model instance. Handy for JSON and quick reads.

Book.objects.values("title", "year")

Pick Only What You Need

Name the fields you pass to values() and Django selects just those columns, keeping each dictionary small and focused.

Book.objects.values("title")

values_list() Returns Tuples

Prefer tuples? values_list() gives each row as a tuple of values in the order you named the fields.

Book.objects.values_list("title", "year")

Flatten a Single Column

Asking for one field? Add flat=True to get a clean list of plain values instead of one-item tuples.

Book.objects.values_list("title", flat=True)

flat Needs One Field

Remember, flat=True only works with a single field. Pass two fields and Django raises an error to keep things clear.

These Are Still QuerySets

Both values() and values_list() stay lazy QuerySets, so you can filter and order them before they ever run.

Book.objects.filter(published=True).values("title")

Count Without Loading

Need just a total? count() asks the database to count rows directly, far cheaper than pulling them all into Python.

Book.objects.filter(published=True).count()

count vs len

Use count() when you only need the number. Calling len() first loads every object, then counts in memory.

Does Anything Match

To check if rows exist, exists() beats count(). It stops at the first match and returns a simple True or False.

Book.objects.filter(year=2024).exists()

Combine for Clean Reads

Mix these freely: filter to narrow, then values_list for a tidy list or count for a total. Each query stays lean.

Book.objects.filter(published=True).values_list("id", flat=True)

Quick Check

You want a plain list of every book title, not tuples or dictionaries. What do you use?

Recap

Wonderful! values() gives dicts, values_list() gives tuples, and count() totals rows in the database. 📊

常见问题解答

「values、values_list 与 count」课时是免费的吗？

是的 — 「values、values_list 与 count」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 Django Academy 课程的其余内容，请升级到 CoddyKit PRO。 Django Academy 课程共包含 4 节课。

「values、values_list 与 count」这节课中我会学到什么？

提取轻量数据并进行聚合你通过在浏览器中直接运行的动手代码来练习 Django 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 Django Academy 需要有经验吗？

无需任何先前经验。CoddyKit 上的 Django 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 4 节课，共 4 节。

「values、values_list 与 count」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 Django Academy 课中编写并运行代码吗？

能。每节 Django 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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