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::{gen::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 gen = settings.into_generator();
    let schema = gen.into_root_schema_for::<MyStruct>();
    println!("{}", serde_json::to_string_pretty(&schema).unwrap());
}

Click to see the output JSON schema...

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