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Accepted
Jack Deeth
Asked: 2025-04-04 05:10:02 +0800 CST

使用 serde 消除样板父 JSON 键

  • 772

我对于如何优雅且轻松地解析消息感到非常印象serde深刻serde_json：

{"msg_type": "asauce", "aaa": 3, "bbb": 14}
{"msg_type": "csyrup", "ccc": 10, "ddd": 20}

// this works!
#[derive(serde::Deserialize, PartialEq, Debug)]
struct AppleSauce {
    aaa: u8,
    bbb: u8,
}

#[derive(serde::Deserialize, PartialEq, Debug)]
struct ChocolateSyrup {
    ccc: u8,
    ddd: u8,
}

#[derive(serde::Deserialize, PartialEq, Debug)]
#[serde(tag = "msg_type")]
enum Sauce {
    #[serde(rename = "asauce")]
    AppleSauce(AppleSauce),
    #[serde(rename = "csyrup")]
    ChocolateSyrup(ChocolateSyrup),
}

#[test]
fn deserialise_inner_applesauce() {
    let json = r#"{"msg_type": "asauce", "aaa": 3, "bbb": 14}"#;
    let expected = AppleSauce { aaa: 3, bbb: 14 };
    let sauce: Sauce = serde_json::from_str(json).unwrap();
    assert_eq!(sauce, Sauce::AppleSauce(expected));
}

但是我的消息有一个父键，我想摆脱它：

{"boilerplate": {"msg_type": "asauce", "aaa": 3, "bbb": 14}}
{"boilerplate": {"msg_type": "csyrup", "ccc": 10, "ddd": 20}}

目前我已经实现了一个from_str方法：

impl Sauce {
    pub fn from_str(msg: &str) -> Option<Sauce> {
        let outer: serde_json::Value = serde_json::from_str(msg).ok()?;
        let inner = &outer["boilerplate"];
        serde_json::from_value(inner.clone()).ok()
    }
}

#[test]
fn deserialise_boilerplate_applesauce_with_helper_method() {
    let json = r#"{"boilerplate": {"msg_type": "asauce", "aaa": 3, "bbb": 14}}"#;
    let expected = AppleSauce { aaa: 3, bbb: 14 };
    let sauce = Sauce::from_str(json).unwrap(); // not serde_json::from_str :(
    assert_eq!(sauce, Sauce::AppleSauce(expected));
}

有没有办法用 serde 属性来省略父键，并消除自定义from_str方法？

我只需要反序列化这些消息（但从我看到的 serde 来看，它可能也会免费序列化）。

json

2 个回答

  1. 有没有办法用 serde 属性来省略父键

    不，没有属性可以做到这一点。您需要定义另一种类型，例如：

    #[derive(serde::Deserialize)]
struct OuterSauce {
    boilerplate: Sauce,
}

    然后对其进行反序列化。或者，您需要一个自定义Deserialize实现，但这很快就会变得笨重，甚至比拥有另一个类型层还要笨重。

    • 2
  2. Best Answer

    您可以创建反映 JSON 的结构（SauceSerde和SauceWrapper），然后impl From<SauceWrapper> for Sauce处理转换。然后，您可以添加#[serde(from = "SauceWrapper")]以便反序列化Sauce使用 的SauceWrapper反序列化逻辑。

    #[derive(serde::Deserialize, PartialEq, Debug)]
pub struct AppleSauce {
    aaa: u8,
    bbb: u8,
}

#[derive(serde::Deserialize, PartialEq, Debug)]
pub struct ChocolateSyrup {
    ccc: u8,
    ddd: u8,
}

#[derive(serde::Deserialize, PartialEq, Debug)]
#[serde(tag = "msg_type")]
// Rename this and keep it private
enum SauceSerde {
    #[serde(rename = "asauce")]
    AppleSauce(AppleSauce),
    #[serde(rename = "csyrup")]
    ChocolateSyrup(ChocolateSyrup),
}

// Make a copy and use `from = "SauceWrapper"`
// Also put `into = "SauceWrapper"` if serializing is needed
#[derive(serde::Deserialize, PartialEq, Debug)]
#[serde(from = "SauceWrapper")]
pub enum Sauce {
    AppleSauce(AppleSauce),
    ChocolateSyrup(ChocolateSyrup),
}

// Make a private wrapper to match the JSON
#[derive(serde::Deserialize, PartialEq, Debug)]
struct SauceWrapper {
    boilerplate: SauceSerde,
}

impl From<SauceWrapper> for Sauce {
    fn from(value: SauceWrapper) -> Self {
        match value.boilerplate {
            SauceSerde::AppleSauce(apple_sauce) => Sauce::AppleSauce(apple_sauce),
            SauceSerde::ChocolateSyrup(chocolate_syrup) => Sauce::ChocolateSyrup(chocolate_syrup),
        }
    }
}

#[test]
fn deserialise_inner_applesauce() {
    let json = r#"{"boilerplate": {"msg_type": "asauce", "aaa": 3, "bbb": 14}}"#;
    let expected = AppleSauce { aaa: 3, bbb: 14 };
    let sauce: Sauce = serde_json::from_str(json).unwrap();
    assert_eq!(sauce, Sauce::AppleSauce(expected));
}
    • 2

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