Function serde_aux::field_attributes::deserialize_default_from_empty_object

pub fn deserialize_default_from_empty_object<'de, D, T>(
    deserializer: D
) -> Result<T, D::Error>where
    D: Deserializer<'de>,
    T: Deserialize<'de> + Default,

Deserializes default value from nullable value or empty object. If the original value is null or {}, Default::default() is used.

Example:

#[macro_use]
extern crate serde_derive;
extern crate serde_json;
extern crate serde_aux;
extern crate serde;

use serde_aux::prelude::*;

#[derive(Serialize, Deserialize, Debug)]
struct MyStruct {
    #[serde(deserialize_with = "deserialize_default_from_empty_object")]
    empty_as_default: Option<MyInnerStruct>,
}

#[derive(Serialize, Deserialize, Debug)]
struct MyInnerStruct {
    mandatory: u64,
}

fn main() {
    let s = r#" { "empty_as_default": { "mandatory": 42 } } "#;
    let a: MyStruct = serde_json::from_str(s).unwrap();
    assert_eq!(a.empty_as_default.unwrap().mandatory, 42);

    let s = r#" { "empty_as_default": null } "#;
    let a: MyStruct = serde_json::from_str(s).unwrap();
    assert!(a.empty_as_default.is_none());

    let s = r#" { "empty_as_default": {} } "#;
    let a: MyStruct = serde_json::from_str(s).unwrap();
    assert!(a.empty_as_default.is_none());

    let s = r#" { "empty_as_default": { "unknown": 42 } } "#;
    assert!(serde_json::from_str::<MyStruct>(s).is_err());
}