使用serde反序列化带有Enum键的HashMap

Question

我有下面的Rust代码，它建模了一个配置文件，其中包括一个HashMap与一个enum键。

use std::collections::HashMap;
use serde::{Deserialize, Serialize};
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq, Hash)]
enum Source {
#[serde(rename = "foo")]
Foo,
#[serde(rename = "bar")]
Bar
}
#[derive(Debug, Clone, Serialize, Deserialize)]
struct SourceDetails {
name: String,
address: String,
}
#[derive(Debug, Clone, Serialize, Deserialize)]
struct Config {
name: String,
main_source: Source,
sources: HashMap<Source, SourceDetails>,
}
fn main() {
let config_str = std::fs::read_to_string("testdata.toml").unwrap();
match toml::from_str::<Config>(&config_str) {
Ok(config) => println!("toml: {:?}", config),
Err(err) => eprintln!("toml: {:?}", err),
}
let config_str = std::fs::read_to_string("testdata.json").unwrap();
match serde_json::from_str::<Config>(&config_str) {
Ok(config) => println!("json: {:?}", config),
Err(err) => eprintln!("json: {:?}", err),
}
}

这是Toml的表示:

name = "big test"
main_source = "foo"
[sources]
foo = { name = "fooname", address = "fooaddr" }
[sources.bar]
name = "barname"
address = "baraddr"

这是JSON表示:

{
"name": "big test",
"main_source": "foo",
"sources": {
"foo": {
"name": "fooname",
"address": "fooaddr"
},
"bar": {
"name": "barname",
"address": "baraddr"
}
}
}

用serde_json反序列化JSON工作完美，但用toml反序列化Toml给出错误。

Error: Error { inner: ErrorInner { kind: Custom, line: Some(5), col: 0, at: Some(77), message: "invalid type: string "foo", expected enum Source", key: ["sources"] } }

如果我将sourcesHashMap更改为String而不是Source，则JSON和Toml都可以正确反序列化。

我对serde和toml很陌生，所以我正在寻找关于如何正确反序列化toml变体的建议。

Answer 1

正如其他人在评论中所说，Toml反序列化器不支持枚举作为键。

您可以先使用serde属性将它们转换为String:

use std::convert::TryFrom;
use std::fmt;
#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq, Hash)]
#[serde(try_from = "String")]
enum Source {
Foo,
Bar
}

然后实现从String:

的转换

struct SourceFromStrError;
impl fmt::Display for SourceFromStrError {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
f.write_str("SourceFromStrError")
}
}
impl TryFrom<String> for Source {
type Error = SourceFromStrError;
fn try_from(s: String) -> Result<Self, Self::Error> {
match s.as_str() {
"foo" => Ok(Source::Foo),
"bar" => Ok(Source::Bar),
_ => Err(SourceFromStrError),
}
}
}

---

如果您只需要对有问题的HashMap进行此操作，则还可以遵循Toml问题中的建议，即保持Source的定义相同，并使用crateserde_with来修改HashMap的序列化方式:

use serde_with::{serde_as, DisplayFromStr};
use std::collections::HashMap;
#[serde_as]
#[derive(Debug, Clone, Serialize, Deserialize)]
struct Config {
name: String,
main_source: Source,
#[serde_as(as = "HashMap<DisplayFromStr, _>")]
sources: HashMap<Source, SourceDetails>,
}

这需要Source的FromStr实现，而不是TryFrom<String>:

impl FromStr for Source {
type Err = SourceFromStrError;
fn from_str(s: &str) -> Result<Self, Self::Err> {
match s {
"foo" => Ok(Source::Foo),
"bar" => Ok(Source::Bar),
_ => Err(SourceFromStrError),
}
}
}