如何使用Serde进行反序列化时转换字段？ [英] How to transform fields during deserialization using Serde?

问题描述

我使用Serde将具有十六进制值 0x400 的XML文件反序列化为一个字符串，我需要将它转换为值 1024 作为 u32 。

我是否需要实现 Visitor trait，这样我就可以将0x分开，然后从基本16解码400到基本10？如果是这样，我该怎么做，以便10个基本整数的反序列化保持不变？

解决方案

deserialize_with 属性

最简单的解决方案是使用 Serde字段属性 deserialize_with 为您的字段设置自定义序列化功能。然后，您可以获取原始字符串并将其转换为适当的：

  extern crate serde; 
＃[macro_use] 
 extern crate serde_derive; 
 extern crate serde_json; 
 
使用serde :: {Deserialize，Deserializer}; 
使用serde :: de :: Error; 
 $ b $ [b] [b] 
 struct EtheriumTransaction {
＃[serde（deserialize_with =from_hex）] 
 account：u64，// hex 
 amount：u64，//十进制
} 
 
 fn from_hex<'de，D>（解串器：D） - >结果< u64，D ::错误> 
其中
 D：反序列化器< de>，
 {
 let s：& str =反序列化::反序列化（反序列化器）？ 
 //比这个
更好的十六进制解码u64 :: from_str_radix（& s [2 ..]，16）.map_err（D :: Error :: custom）
} 
 
 fn main（）{
 let raw = r＃{account：0xDEADBEEF，amount：100}＃; 
 let transaction：EtheriumTransaction = 
 serde_json :: from_str（raw）.expect（Could not derserialize）; 
 assert_eq！（transaction.amount，100）; 
 assert_eq！（transaction.account，0xDEAD_BEEF）; 
} 
  

playground
$ b

实现 serde :: Deserialize $ b pre
$ b

从这里开始，将它推广到自己的类型以允许重用它是一小步：

 ＃[derive（Debug，Deserialize）] 
 struct EtheriumTransaction {
 account：Account，// hex 
 amount：u64，// decimal 
 
 $ b $＃[derive（Debug，PartialEq）] 
 struct Account（u64）; 
 
 impl<'de>反序列化<去>用于帐户{
 fn反序列化< D>（反序列化器：D） - >结果< Self，D :: Error> 
其中
 D：反序列化器< de>，
 {
 let s：& str =反序列化::反序列化（反序列化器）？ 
 //比这个
更好的十六进制解码u64 :: from_str_radix（& s [2 ..]，16）
 .map（Account）
 .map_err（D： ：Error :: custom）
} 
} 
  

playground

请注意，使用任何其他现有的Serde实现来解码。在这里，我们解码为一个字符串片段（ let s：& str = Deserialize :: deserialize（deserializer）？）。

此方法允许您添加或删除字段，因为内部反序列化类型可以根据需要进行任何操作。

另请参阅：

• 如何在使用Serde序列化期间转换字段？

I'm using Serde to deserialize an XML file which has the hex value 0x400 as a string and I need to convert it to the value 1024 as a u32.

Do I need to implement the Visitor trait so that I separate 0x and then decode 400 from base 16 to base 10? If so, how do I do that so that deserialization for base 10 integers remains intact?

解决方案

The deserialize_with attribute

The easiest solution is to use the Serde field attribute deserialize_with to set a custom serialization function for your field. You then can get the raw string and convert it as appropriate:

extern crate serde;
#[macro_use]
extern crate serde_derive;
extern crate serde_json;

use serde::{Deserialize, Deserializer};
use serde::de::Error;

#[derive(Debug, Deserialize)]
struct EtheriumTransaction {
    #[serde(deserialize_with = "from_hex")]
    account: u64, // hex
    amount: u64,  // decimal
}

fn from_hex<'de, D>(deserializer: D) -> Result<u64, D::Error>
where
    D: Deserializer<'de>,
{
    let s: &str = Deserialize::deserialize(deserializer)?;
    // do better hex decoding than this
    u64::from_str_radix(&s[2..], 16).map_err(D::Error::custom)
}

fn main() {
    let raw = r#"{"account": "0xDEADBEEF", "amount": 100}"#;
    let transaction: EtheriumTransaction =
        serde_json::from_str(raw).expect("Couldn't derserialize");
    assert_eq!(transaction.amount, 100);
    assert_eq!(transaction.account, 0xDEAD_BEEF);
}

playground

Implement serde::Deserialize

From here, it's a tiny step to promoting it to your own type to allow reusing it:

#[derive(Debug, Deserialize)]
struct EtheriumTransaction {
    account: Account, // hex
    amount: u64,      // decimal
}

#[derive(Debug, PartialEq)]
struct Account(u64);

impl<'de> Deserialize<'de> for Account {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        let s: &str = Deserialize::deserialize(deserializer)?;
        // do better hex decoding than this
        u64::from_str_radix(&s[2..], 16)
            .map(Account)
            .map_err(D::Error::custom)
    }
}

playground

Note how this can use any other existing Serde implementation to decode. Here, we decode to a string slice (let s: &str = Deserialize::deserialize(deserializer)?).

This method allows you to also add or remove fields as the "inner" deserialized type can do basically whatever it wants.

See also:

• How to transform fields during serialization using Serde?

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