CODEWITHSUNDEEP
jsondeserializationrust
Aleksandr
Aleksandr

Reputation: 1465

How to decode a JSON value that can be a String or null?

I am trying to decode JSON in Rust.

JSON examples:

[{"id": 1234, "rank": 44, "author": null}]
[{"id": 1234, "rank": 44, "author": "Some text"}]

If I use String for the author field:

#[derive(Show, RustcDecodable, RustcEncodable)]
pub struct TestStruct {
    pub id: u64,
    pub rank: i64,
    pub author: String,
}

It throws the error:

thread '<main>' panicked at 'called `Result::unwrap()` on an `Err` value: ExpectedError("String", "null")', /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/libcore/result.rs:742

How can I decode (filter/ignore null) this JSON value?

Upvotes: 2

Views: 227

Answers (1)

Francis Gagn&#233;
Francis Gagn&#233;

Reputation: 65782

Change the type of author from String to Option<String>.

#[derive(Show, RustcDecodable, RustcEncodable)]
pub struct TestStruct {
    pub id: u64,
    pub rank: i64,
    pub author: Option<String>,
}

Results:

Ok([TestStruct { id: 1234u64, rank: 44i64, author: None }]
Ok([TestStruct { id: 1234u64, rank: 44i64, author: "Some text" }])

Upvotes: 4

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