285 lines
8.4 KiB
Markdown
285 lines
8.4 KiB
Markdown
# Schemars
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> [!NOTE]
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> This branch is for the current v1 alpha version of Schemars which is still under development.
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> For the current stable release of Schemars (v0.8.x), see the [v0 branch](https://github.com/GREsau/schemars/tree/v0).
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>
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> For information on migrating from 0.8 to 1.0, see [the migration guide](https://graham.cool/schemars/migrating/).
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[](https://github.com/GREsau/schemars/actions)
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[](https://crates.io/crates/schemars)
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[](https://docs.rs/schemars/1.0.0--latest)
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[](https://blog.rust-lang.org/2022/04/07/Rust-1.60.0.html)
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Generate JSON Schema documents from Rust code
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## Basic Usage
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If you don't really care about the specifics, the easiest way to generate a JSON schema for your types is to `#[derive(JsonSchema)]` and use the `schema_for!` macro. All fields of the type must also implement `JsonSchema` - Schemars implements this for many standard library types.
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```rust
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use schemars::{schema_for, JsonSchema};
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#[derive(JsonSchema)]
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pub struct MyStruct {
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pub my_int: i32,
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pub my_bool: bool,
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pub my_nullable_enum: Option<MyEnum>,
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}
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#[derive(JsonSchema)]
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pub enum MyEnum {
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StringNewType(String),
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StructVariant { floats: Vec<f32> },
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}
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let schema = schema_for!(MyStruct);
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println!("{}", serde_json::to_string_pretty(&schema).unwrap());
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```
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<details>
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<summary>Click to see the output JSON schema...</summary>
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```json
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{
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"$schema": "https://json-schema.org/draft/2020-12/schema",
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"title": "MyStruct",
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"type": "object",
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"properties": {
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"my_bool": {
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"type": "boolean"
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},
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"my_int": {
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"type": "integer",
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"format": "int32"
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},
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"my_nullable_enum": {
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"anyOf": [
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{
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"$ref": "#/$defs/MyEnum"
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},
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{
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"type": "null"
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}
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]
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}
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},
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"required": ["my_int", "my_bool"],
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"$defs": {
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"MyEnum": {
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"oneOf": [
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{
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"type": "object",
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"properties": {
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"StringNewType": {
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"type": "string"
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}
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},
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"additionalProperties": false,
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"required": ["StringNewType"]
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},
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{
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"type": "object",
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"properties": {
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"StructVariant": {
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"type": "object",
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"properties": {
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"floats": {
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"type": "array",
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"items": {
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"type": "number",
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"format": "float"
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}
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}
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},
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"required": ["floats"]
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}
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},
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"additionalProperties": false,
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"required": ["StructVariant"]
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}
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]
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}
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}
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}
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```
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</details>
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### Serde Compatibility
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One of the main aims of this library is compatibility with [Serde](https://github.com/serde-rs/serde). Any generated schema _should_ match how [serde_json](https://github.com/serde-rs/json) would serialize/deserialize to/from JSON. To support this, Schemars will check for any `#[serde(...)]` attributes on types that derive `JsonSchema`, and adjust the generated schema accordingly.
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```rust
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use schemars::{schema_for, JsonSchema};
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use serde::{Deserialize, Serialize};
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#[derive(Deserialize, Serialize, JsonSchema)]
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#[serde(rename_all = "camelCase", deny_unknown_fields)]
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pub struct MyStruct {
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#[serde(rename = "myNumber")]
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pub my_int: i32,
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pub my_bool: bool,
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#[serde(default)]
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pub my_nullable_enum: Option<MyEnum>,
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}
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#[derive(Deserialize, Serialize, JsonSchema)]
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#[serde(untagged)]
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pub enum MyEnum {
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StringNewType(String),
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StructVariant { floats: Vec<f32> },
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}
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let schema = schema_for!(MyStruct);
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println!("{}", serde_json::to_string_pretty(&schema).unwrap());
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```
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<details>
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<summary>Click to see the output JSON schema...</summary>
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```json
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{
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"$schema": "https://json-schema.org/draft/2020-12/schema",
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"title": "MyStruct",
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"type": "object",
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"properties": {
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"myBool": {
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"type": "boolean"
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},
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"myNullableEnum": {
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"anyOf": [
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{
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"$ref": "#/$defs/MyEnum"
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},
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{
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"type": "null"
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}
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],
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"default": null
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},
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"myNumber": {
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"type": "integer",
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"format": "int32"
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}
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},
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"additionalProperties": false,
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"required": ["myNumber", "myBool"],
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"$defs": {
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"MyEnum": {
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"anyOf": [
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{
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"type": "string"
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},
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{
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"type": "object",
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"properties": {
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"floats": {
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"type": "array",
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"items": {
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"type": "number",
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"format": "float"
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}
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}
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},
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"required": ["floats"]
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}
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]
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}
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}
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}
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```
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</details>
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`#[serde(...)]` attributes can be overriden using `#[schemars(...)]` attributes, which behave identically (e.g. `#[schemars(rename_all = "camelCase")]`). You may find this useful if you want to change the generated schema without affecting Serde's behaviour, or if you're just not using Serde.
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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. 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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use schemars::schema_for_value;
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use serde::Serialize;
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#[derive(Serialize)]
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pub struct MyStruct {
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pub my_int: i32,
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pub my_bool: bool,
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pub my_nullable_enum: Option<MyEnum>,
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}
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#[derive(Serialize)]
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pub enum MyEnum {
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StringNewType(String),
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StructVariant { floats: Vec<f32> },
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}
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let schema = schema_for_value!(MyStruct {
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my_int: 123,
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my_bool: true,
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my_nullable_enum: Some(MyEnum::StringNewType("foo".to_string()))
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});
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println!("{}", serde_json::to_string_pretty(&schema).unwrap());
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```
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<details>
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<summary>Click to see the output JSON schema...</summary>
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```json
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{
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"$schema": "http://json-schema.org/draft-07/schema#",
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"title": "MyStruct",
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"examples": [
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{
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"my_bool": true,
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"my_int": 123,
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"my_nullable_enum": {
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"StringNewType": "foo"
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}
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}
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],
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"type": "object",
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"properties": {
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"my_bool": {
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"type": "boolean"
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},
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"my_int": {
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"type": "integer"
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},
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"my_nullable_enum": true
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}
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}
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```
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</details>
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## Feature Flags
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- `std` (enabled by default) - implements `JsonSchema` for types in the rust standard library (`JsonSchema` is still implemented on types in `core` and `alloc`, even when this feature is disabled). Disable this feature to use schemars in `no_std` environments.
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- `derive` (enabled by default) - provides `#[derive(JsonSchema)]` macro
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- `preserve_order` - keep the order of struct fields in `Schema` properties
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- `raw_value` - implements `JsonSchema` for `serde_json::value::RawValue` (enables the serde_json `raw_value` feature)
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Schemars can implement `JsonSchema` on types from several popular crates, enabled via feature flags (dependency versions are shown in brackets):
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- `arrayvec07` - [arrayvec](https://crates.io/crates/arrayvec) (^0.7)
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- `bigdecimal04` - [bigdecimal](https://crates.io/crates/bigdecimal) (^0.4)
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- `bytes1` - [bytes](https://crates.io/crates/bytes) (^1.0)
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- `chrono04` - [chrono](https://crates.io/crates/chrono) (^0.4)
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- `either1` - [either](https://crates.io/crates/either) (^1.3)
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- `enumset1` - [enumset](https://crates.io/crates/enumset) (^1.0)
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- `indexmap2` - [indexmap](https://crates.io/crates/indexmap) (^2.0)
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- `rust_decimal1` - [rust_decimal](https://crates.io/crates/rust_decimal) (^1.0)
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- `semver1` - [semver](https://crates.io/crates/semver) (^1.0.9)
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- `smallvec1` - [smallvec](https://crates.io/crates/smallvec) (^1.0)
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- `smol_str02` - [smol_str](https://crates.io/crates/smol_str) (^0.2.1)
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- `url2` - [url](https://crates.io/crates/url) (^2.0)
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- `uuid1` - [uuid](https://crates.io/crates/uuid) (^1.0)
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For example, to implement `JsonSchema` on types from `chrono`, enable it as a feature in the `schemars` dependency in your `Cargo.toml` like so:
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```toml
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[dependencies]
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schemars = { version = "1.0.0-alpha.6", features = ["chrono04"] }
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```
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