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

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

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Formats the value using the given formatter. Read more

Returns the “default value” for a type. Read more

Deserialize this value from the given Serde deserializer.

Serialize this value into the given Serde serializer.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

Uses borrowed data to replace owned data, usually by cloning. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.