This page is for the current v1 alpha version of Schemars. This version is still under development, and further breaking changes may be introduced.

To view this page for the current stable release of Schemars (v0.8.x), click here.

Custom Schema Settings

The generate 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"
          ]
        }
      ]
    }
  }
}