This page is for the current stable release of Schemars (v0.8.x).

To view this page for the v1 version of Schemars, which is still under development, click here.

Custom Schema Settings

The gen module allows you to customise how schemas are generated. For example, the default behaviour for Option<T> is to include null in the schema's types, but we can instead add a nullable property to its schema:

use schemars::{generate::SchemaSettings, JsonSchema};

#[derive(JsonSchema)]
pub struct MyStruct {
    pub my_int: i32,
    pub my_bool: bool,
    pub my_nullable_enum: Option<MyEnum>,
}

#[derive(JsonSchema)]
pub enum MyEnum {
    StringNewType(String),
    StructVariant { floats: Vec<f32> },
}

fn main() {
    let settings = SchemaSettings::draft07().with(|s| {
        s.option_nullable = true;
        s.option_add_null_type = false;
    });
    let generator = settings.into_generator();
    let schema = generator.into_root_schema_for::<MyStruct>();
    println!("{}", serde_json::to_string_pretty(&schema).unwrap());
}

Click to see the output JSON schema...

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "title": "MyStruct",
  "type": "object",
  "properties": {
    "my_bool": {
      "type": "boolean"
    },
    "my_int": {
      "type": "integer",
      "format": "int32"
    },
    "my_nullable_enum": {
      "allOf": [
        {
          "$ref": "#/definitions/MyEnum"
        }
      ],
      "nullable": true
    }
  },
  "required": [
    "my_int",
    "my_bool"
  ],
  "definitions": {
    "MyEnum": {
      "oneOf": [
        {
          "type": "object",
          "properties": {
            "StringNewType": {
              "type": "string"
            }
          },
          "additionalProperties": false,
          "required": [
            "StringNewType"
          ]
        },
        {
          "type": "object",
          "properties": {
            "StructVariant": {
              "type": "object",
              "properties": {
                "floats": {
                  "type": "array",
                  "items": {
                    "type": "number",
                    "format": "float"
                  }
                }
              },
              "required": [
                "floats"
              ]
            }
          },
          "additionalProperties": false,
          "required": [
            "StructVariant"
          ]
        }
      ]
    }
  }
}