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111 lines
4.4 KiB
Markdown
111 lines
4.4 KiB
Markdown
# FastAPI Response Model with SQLModel
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Now I'll show you how to use FastAPI's `response_model` with **SQLModel**.
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## Interactive API Docs
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Up to now, with the code we have used, the API docs know the data the clients have to send:
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<img class="shadow" alt="Interactive API docs UI" src="/img/tutorial/fastapi/simple-hero-api/image01.png">
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This interactive docs UI is powered by <a href="https://github.com/swagger-api/swagger-ui" class="external-link" target="_blank">Swagger UI</a>, and what Swagger UI does is to read a big JSON content that defines the API with all the data schemas (data shapes) using the standard <a href="https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.0.3.md" class="external-link" target="_blank">OpenAPI</a>, and showing it in that nice <abbr title="User Interface">UI</abbr>.
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FastAPI automatically **generates that OpenAPI** for Swagger UI to read it.
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And it generates it **based on the code you write**, using the Pydantic models (in this case **SQLModel** models) and type annotations to know the schemas of the data that the API handles.
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## Response Data
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But up to now, the API docs UI doesn't know the schema of the *responses* our app sends back.
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You can see that there's a possible "Successful Response" with a code `200`, but we have no idea how the response data would look like.
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<img class="shadow" alt="API docs UI without response data schemas" src="/img/tutorial/fastapi/response-model/image01.png">
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Right now, we only tell FastAPI the data we want to receive, but we don't tell it yet the data we want to send back.
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Let's do that now. 🤓
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## Use `response_model`
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We can use `response_model` to tell FastAPI the schema of the data we want to send back.
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For example, we can pass the same `Hero` **SQLModel** class (because it is also a Pydantic model):
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```Python hl_lines="3"
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# Code above omitted 👆
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{!./docs_src/tutorial/fastapi/response_model/tutorial001.py[ln:33-39]!}
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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/response_model/tutorial001.py!}
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```
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</details>
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## List of Heroes in `response_model`
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We can also use other type annotations, the same way we can use with Pydantic fields. For example, we can pass a list of `Hero`s.
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First, we import `List` from `typing` and then we declare the `response_model` with `List[Hero]`:
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```Python hl_lines="1 5"
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{!./docs_src/tutorial/fastapi/response_model/tutorial001.py[ln:1]!}
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# Code here omitted 👈
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{!./docs_src/tutorial/fastapi/response_model/tutorial001.py[ln:42-46]!}
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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/response_model/tutorial001.py!}
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```
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</details>
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## FastAPI and Response Model
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FastAPI will do data validation and filtering of the response with this `response_model`.
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So this works like a contract between our application and the client.
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You can read more about it in the <a href="https://fastapi.tiangolo.com/tutorial/response-model/" class="external-link" target="_blank">FastAPI docs about `response_model`</a>.
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## New API Docs UI
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Now we can go back to the docs UI and see that they now show the schema of the response we will receive.
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<img class="shadow" alt="API docs UI without response data schemas" src="/img/tutorial/fastapi/response-model/image02.png">
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The clients will know what data they should expect.
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## Automatic Clients
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The most visible advantage of using the `response_model` is that it shows up in the API docs UI.
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But there are other advantages, like that FastAPI will do automatic <a href="https://fastapi.tiangolo.com/tutorial/response-model/" class="external-link" target="_blank">data validation and filtering</a> of the response data using this model.
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Additionally, because the schemas are defined in using a standard, there are many tools that can take advantage of this.
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For example, client generators, that can automatically create the code necessary to talk to your API in many languages.
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!!! info
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If you are curious about the standards, FastAPI generates OpenAPI, that internally uses JSON Schema.
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You can read about all that in the <a href="https://fastapi.tiangolo.com/tutorial/first-steps/#openapi" class="external-link" target="_blank">FastAPI docs - First Steps</a>.
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## Recap
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Use the `response_model` to tell FastAPI the schema of the data you want to send back and have awesome data APIs. 😎
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