如何解决Axum中枚举作为查询参数的反序列化报错？

问题核心在于serde默认的枚举反序列化逻辑：它期望结构化输入（如JSON对象形式），但查询参数传递的是纯字符串值（如Male），导致解析失败。以下是两种修复方案：

方案一：通过TryFrom配合serde属性实现 #

修改枚举定义，添加serde属性并实现TryFrom<String> trait，让serde能够将字符串值转换为枚举变体：

use serde::{Deserialize, Serialize};

#[derive(Debug, Deserialize, Serialize)]
#[serde(try_from = "String")]
pub enum Gender {
    Male,
    Female,
    NonBinary,
}

impl TryFrom<String> for Gender {
    type Error = String;

    fn try_from(value: String) -> Result<Self, Self::Error> {
        match value.as_str() {
            "Male" => Ok(Gender::Male),
            "Female" => Ok(Gender::Female),
            "NonBinary" => Ok(Gender::NonBinary),
            _ => Err(format!("无效的性别值: {}", value)),
        }
    }
}

方案二：实现FromStr trait #

通过实现标准库的FromStr trait，配合自定义反序列化函数，让Axum的Query提取器直接解析字符串参数：

use serde::{Deserialize, Serialize};
use std::str::FromStr;

#[derive(Debug, Deserialize, Serialize)]
#[serde(deserialize_with = "deserialize_gender_from_str")]
pub enum Gender {
    Male,
    Female,
    NonBinary,
}

impl FromStr for Gender {
    type Err = String;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        match s {
            "Male" => Ok(Gender::Male),
            "Female" => Ok(Gender::Female),
            "NonBinary" => Ok(Gender::NonBinary),
            _ => Err(format!("无效的性别值: {}", s)),
        }
    }
}

// 自定义反序列化函数，调用FromStr完成转换
fn deserialize_gender_from_str<'de, D>(deserializer: D) -> Result<Gender, D::Error>
where
    D: serde::Deserializer<'de>,
{
    let s = String::deserialize(deserializer)?;
    Gender::from_str(&s).map_err(serde::de::Error::custom)
}

使用任意一种方案后，http://localhost:3000/greet?gender=Male这类请求就能正确解析出Gender::Male枚举值。

内容的提问来源于stack exchange，提问作者Finlay Weber