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62 lines
2.3 KiB
Markdown
62 lines
2.3 KiB
Markdown
# Body - Fields { #body-fields }
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The same way you can declare additional validation and metadata in *path operation function* parameters with `Query`, `Path` and `Body`, you can declare validation and metadata inside of Pydantic models using Pydantic's `Field`.
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## Import `Field` { #import-field }
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First, you have to import it:
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{* ../../docs_src/body_fields/tutorial001_an_py310.py hl[4] *}
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/// warning
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Notice that `Field` is imported directly from `pydantic`, not from `fastapi` as are all the rest (`Query`, `Path`, `Body`, etc).
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///
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## Declare model attributes { #declare-model-attributes }
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You can then use `Field` with model attributes:
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{* ../../docs_src/body_fields/tutorial001_an_py310.py hl[11:14] *}
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`Field` works the same way as `Query`, `Path` and `Body`, it has all the same parameters, etc.
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/// note | Technical Details
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Actually, `Query`, `Path` and others you'll see next create objects of subclasses of a common `Param` class, which is itself a subclass of Pydantic's `FieldInfo` class.
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And Pydantic's `Field` returns an instance of `FieldInfo` as well.
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`Body` also returns objects of a subclass of `FieldInfo` directly. And there are others you will see later that are subclasses of the `Body` class.
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Remember that when you import `Query`, `Path`, and others from `fastapi`, those are actually functions that return special classes.
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///
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/// tip
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Notice how each model's attribute with a type, default value and `Field` has the same structure as a *path operation function's* parameter, with `Field` instead of `Path`, `Query` and `Body`.
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///
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## Add extra information { #add-extra-information }
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You can declare extra information in `Field`, `Query`, `Body`, etc. And it will be included in the generated JSON Schema.
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You will learn more about adding extra information later in the docs, when learning to declare examples.
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/// warning
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Extra keys passed to `Field` will also be present in the resulting OpenAPI schema for your application.
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As these keys may not necessarily be part of the OpenAPI specification, some OpenAPI tools, for example [the OpenAPI validator](https://validator.swagger.io/), may not work with your generated schema.
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///
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## Recap { #recap }
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You can use Pydantic's `Field` to declare extra validations and metadata for model attributes.
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You can also use the extra keyword arguments to pass additional JSON Schema metadata.
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