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65 lines
2.5 KiB
Markdown
65 lines
2.5 KiB
Markdown
# Read Heroes with Limit and Offset with FastAPI
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When a client sends a request to get all the heroes, we have been returning them all.
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But if we had **thousands** of heroes that could consume a lot of **computational resources**, network bandwith, etc.
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So we probably want to limit it.
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Let's use the same **offset** and **limit** we learned about in the previous tutorial chapters for the API.
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!!! info
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In many cases this is also called **pagination**.
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## Add a Limit and Offset to the Query Parameters
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Let's add `limit` and `offset` to the query parameters.
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By default, we will return the first results from the database, so `offset` will have a default value of `0`.
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And by default, we will return a maximum of `100` heroes, so `limit` will have a default value of `100`.
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```Python hl_lines="3 9 11"
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{!./docs_src/tutorial/fastapi/limit_and_offset/tutorial001.py[ln:1-4]!}
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# Code here omitted 👈
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{!./docs_src/tutorial/fastapi/limit_and_offset/tutorial001.py[ln:54-58]!}
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# Code below omitted 👇
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```
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<details>
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<summary>👀 Full file preview</summary>
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```Python
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{!./docs_src/tutorial/fastapi/limit_and_offset/tutorial001.py!}
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```
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</details>
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We want to allow clients to set a different `offset` and `limit` values.
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But we don't want them to be able to set a `limit` of something like `9999`, that's over `9000`! 😱
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So, to prevent it, we add additional validation to the `limit` query parameter, declaring that it has to be **l**ess **t**han or **e**qual to `100` with `lte=100`.
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This way, a client can decide to take less heroes if they want, but not more.
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!!! info
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If you need to refresh how query parameters and their validation work, check out the docs in FastAPI:
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* <a href="https://fastapi.tiangolo.com/tutorial/query-params/" class="external-link" target="_blank">Query Parameters</a>
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* <a href="https://fastapi.tiangolo.com/tutorial/query-params-str-validations/" class="external-link" target="_blank">Query Parameters and String Validations</a>
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* <a href="https://fastapi.tiangolo.com/tutorial/path-params-numeric-validations/" class="external-link" target="_blank">Path Parameters and Numeric Validations</a>
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## Check the Docs UI
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Now we can see that the docs UI shows the new parameters to control **limit** and **offset** of our data.
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<img class="shadow" alt="Interactive API docs UI" src="/img/tutorial/fastapi/limit-and-offset/image01.png">
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## Recap
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You can use **FastAPI**'s automatic data validation to get the parameters for `limit` and `offset`, and then use them with the **session** to control ranges of data to be sent in responses.
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