Struct serde_with::DefaultOnError

pub struct DefaultOnError<T = Same>(_);

Deserialize value and return Default on error

The main use case is ignoring error while deserializing. Instead of erroring, it simply deserializes the Default variant of the type. It is not possible to find the error location, i.e., which field had a deserialization error, with this method. During serialization this wrapper does nothing. The serialization behavior of the underlying type is preserved. The type must implement Default for this conversion to work.

The same functionality is also available as serde_with::rust::default_on_error compatible with serde’s with-annotation.

Examples

#[serde_as]
#[derive(Deserialize, Debug)]
struct A {
    #[serde_as(deserialize_as = "DefaultOnError")]
    value: u32,
}

let a: A = serde_json::from_str(r#"{"value": 123}"#).unwrap();
assert_eq!(123, a.value);

// null is of invalid type
let a: A = serde_json::from_str(r#"{"value": null}"#).unwrap();
assert_eq!(0, a.value);

// String is of invalid type
let a: A = serde_json::from_str(r#"{"value": "123"}"#).unwrap();
assert_eq!(0, a.value);

// Map is of invalid type
let a: A = dbg!(serde_json::from_str(r#"{"value": {}}"#)).unwrap();
assert_eq!(0, a.value);

// Missing entries still cause errors
assert!(serde_json::from_str::<A>(r#"{  }"#).is_err());

Deserializing missing values can be supported by adding the default field attribute:

#[serde_as]
#[derive(Deserialize)]
struct B {
    #[serde_as(deserialize_as = "DefaultOnError")]
    #[serde(default)]
    value: u32,
}

let b: B = serde_json::from_str(r#"{  }"#).unwrap();
assert_eq!(0, b.value);

DefaultOnError can be combined with other conversion methods. In this example, we deserialize a Vec, each element is deserialized from a string. If the string does not parse as a number, then we get the default value of 0.

#[serde_as]
#[derive(Serialize, Deserialize)]
struct C {
    #[serde_as(as = "Vec<DefaultOnError<DisplayFromStr>>")]
    value: Vec<u32>,
};

let c: C = serde_json::from_value(json!({
    "value": ["1", "2", "a3", "", {}, "6"]
})).unwrap();
assert_eq!(vec![1, 2, 0, 0, 0, 6], c.value);

Trait Implementations

impl<T: Clone> Clone for DefaultOnError<T>

fn clone(&self) -> DefaultOnError<T>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Debug> Debug for DefaultOnError<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T: Default> Default for DefaultOnError<T>

fn default() -> DefaultOnError<T>

Returns the “default value” for a type.

impl<'de, T, TAs> DeserializeAs<'de, T> for DefaultOnError<TAs> where
    TAs: DeserializeAs<'de, T>,
    T: Default, 

fn deserialize_as<D>(deserializer: D) -> Result<T, D::Error> where
    D: Deserializer<'de>, 

Deserialize this value from the given Serde deserializer.

impl<T, TAs> SerializeAs<T> for DefaultOnError<TAs> where
    TAs: SerializeAs<T>, 

fn serialize_as<S>(source: &T, serializer: S) -> Result<S::Ok, S::Error> where
    S: Serializer, 

Serialize this value into the given Serde serializer.

impl<T: Copy> Copy for DefaultOnError<T>