35 lines
1.9 KiB
Markdown
35 lines
1.9 KiB
Markdown
---
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title: Generating Schemas
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nav_order: 4
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permalink: /v0/generating/
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---
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# Generating Schemas
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The easiest way to generate a schema for a type that implements is to use the [`schema_for!` macro](https://docs.rs/schemars/latest/schemars/macro.schema_for.html), like so:
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```rust
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let my_schema = schema_for!(MyStruct);
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```
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This will create a schema that conforms to [JSON Schema Draft 7](https://json-schema.org/specification-links.html#draft-7), but this is liable to change in a future version of Schemars if support for other JSON Schema versions is added.
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If you want more control over how the schema is generated, you can use the [`gen` module](https://docs.rs/schemars/latest/schemars/gen/). There are two main types in this module:
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- [`SchemaSettings`](https://docs.rs/schemars/latest/schemars/gen/struct.SchemaSettings.html), which defines what JSON Schema features should be used when generating schemas (for example, how `Option`s should be represented).
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- [`SchemaGenerator`](https://docs.rs/schemars/latest/schemars/gen/struct.SchemaGenerator.html), which manages the generation of a schema document.
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See the API documentation for more info on how to use those types for custom schema generation.
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## Schema from Example Value
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If you want a schema for a type that can't/doesn't implement `JsonSchema`, but does implement `serde::Serialize`, then you can generate a JSON schema from a value of that type using the [`schema_for_value!` macro](https://docs.rs/schemars/latest/schemars/macro.schema_for_value.html). However, this schema will generally be less precise than if the type implemented `JsonSchema` - particularly when it involves enums, since schemars will not make any assumptions about the structure of an enum based on a single variant.
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```rust
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let value = MyStruct { foo = 123 };
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let my_schema = schema_for_value!(value);
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```
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<!-- TODO:
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create and link to example
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-->
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