[英]Using serde_json to serialise maps with non-String keys
我写了一个测试用例:
use serde::{Serialize, Deserialize};
use std::collections::BTreeMap;
use std::fmt;
#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, PartialOrd, Ord)]
struct Incline {
rise: u8,
distance: u8,
}
impl Incline {
pub fn new(rise: u8, distance: u8) -> Incline {
Incline {rise, distance}
}
}
impl fmt::Display for Incline {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "{}:{}", self.rise, self.distance)
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn display_format() {
let incline = Incline::new(4, 3);
assert_eq!(format!("{}", incline), "4:3");
}
#[test]
fn serialisation() {
let key = Incline::new(4, 3);
let value = "a steep hill";
let mut map: BTreeMap<Incline, &str> = BTreeMap::new();
map.insert(key, value);
let serialised = serde_json::to_string(&map).unwrap();
assert_eq!(serialised, r#"{"4:3":"a steep hill"}"#);
}
}
display_format
测试按预期通过。
serialisation
测试失败并出现错误:
thread 'tests::serialisation' panicked at 'called `Result::unwrap()` on an `Err` value: Error("key must be a string", line: 0, column: 0)', src/lib.rs:40:54
如何告诉 serde_json 使用Incline
的std::fmt::Display::fmt
实现将 Incline Incline::new(4,3)
变成"4:3"
?
通过更多搜索,我意识到我必须自己实现序列化。
这可以完成工作:
use serde::{Serialize, Serializer};
#[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
struct Incline {
rise: u8,
distance: u8,
}
impl Incline {
pub fn new(rise: u8, distance: u8) -> Incline {
Incline {rise, distance}
}
}
impl Serialize for Incline {
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: Serializer,
{
serializer.serialize_str(&format!("{}:{}", self.rise, self.distance))
}
}
#[cfg(test)]
mod tests {
use std::collections::BTreeMap;
use super::*;
#[test]
fn serialisation() {
let key = Incline::new(4, 3);
let value = "a steep hill";
let mut map: BTreeMap<Incline, &str> = BTreeMap::new();
map.insert(key, value);
let serialised = serde_json::to_string(&map).unwrap();
assert_eq!(serialised, r#"{"4:3":"a steep hill"}"#);
}
}
完整的序列化和反序列化看起来像:
use serde::{Serialize, Serializer, Deserialize, Deserializer};
use serde::de::{self, Visitor, Unexpected};
use std::fmt;
use std::str::FromStr;
use regex::Regex;
#[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
struct Incline {
rise: u8,
distance: u8,
}
impl Incline {
pub fn new(rise: u8, distance: u8) -> Incline {
Incline {rise, distance}
}
}
impl Serialize for Incline {
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: Serializer,
{
serializer.serialize_str(&format!("{}:{}", self.rise, self.distance))
}
}
struct InclineVisitor;
impl<'de> Visitor<'de> for InclineVisitor {
type Value = Incline;
fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
formatter.write_str("a colon-separated pair of integers between 0 and 255")
}
fn visit_str<E>(self, s: &str) -> Result<Self::Value, E>
where
E: de::Error,
{
let re = Regex::new(r"(\d+):(\d+)").unwrap(); // PERF: move this into a lazy_static!
if let Some(nums) = re.captures_iter(s).next() {
if let Ok(rise) = u8::from_str(&nums[1]) { // nums[0] is the whole match, so we must skip that
if let Ok(distance) = u8::from_str(&nums[2]) {
Ok(Incline::new(rise, distance))
} else {
Err(de::Error::invalid_value(Unexpected::Str(s), &self))
}
} else {
Err(de::Error::invalid_value(Unexpected::Str(s), &self))
}
} else {
Err(de::Error::invalid_value(Unexpected::Str(s), &self))
}
}
}
impl<'de> Deserialize<'de> for Incline {
fn deserialize<D>(deserializer: D) -> Result<Incline, D::Error>
where
D: Deserializer<'de>,
{
deserializer.deserialize_string(InclineVisitor)
}
}
#[cfg(test)]
mod tests {
use std::collections::BTreeMap;
use super::*;
#[test]
fn serialisation() {
let key = Incline::new(4, 3);
let value = "a steep hill";
let mut map: BTreeMap<Incline, &str> = BTreeMap::new();
map.insert(key, value);
let serialised = serde_json::to_string(&map).unwrap();
assert_eq!(serialised, r#"{"4:3":"a steep hill"}"#);
}
#[test]
fn deserialisation() {
let json = r#"{"4:3":"a steep hill"}"#;
let deserialised: BTreeMap<Incline, &str> = serde_json::from_str(&json).unwrap();
let key = Incline::new(4, 3);
let value = "a steep hill";
let mut map: BTreeMap<Incline, &str> = BTreeMap::new();
map.insert(key, value);
assert_eq!(deserialised, map);
}
}
我写了一个板条箱,用 serde_json: serde_json_any_key对非字符串键进行通用反序列化。 它支持通过自由函数对顶层映射进行序列化,并通过#[serde(with)] 属性支持结构内的嵌套映射。 对于 OP 的例子:
#[derive(Serialize, Deserialize, Debug, PartialEq, Eq, PartialOrd, Ord)]
struct Incline {
rise: u8,
distance: u8,
}
impl Incline {
pub fn new(rise: u8, distance: u8) -> Incline {
Incline {rise, distance}
}
}
#[cfg(test)]
mod tests {
use serde::{Serialize, Deserialize};
use serde_json_any_key::*;
use std::collections::BTreeMap;
use super::*;
static JSON: &str = r#"{"{\"rise\":4,\"distance\":3}":"a steep hill"}"#;
#[test]
fn test_serialisation() {
let key = Incline::new(4, 3);
let value = "a steep hill".to_owned();
let mut map: BTreeMap<Incline, String> = BTreeMap::new();
map.insert(key, value);
let serialised = map.to_json_map().unwrap();
println!("{}", serialised);
assert_eq!(serialised, JSON);
}
#[test]
fn test_deserialisation() {
let deserialised: BTreeMap<Incline, String> =
json_to_iter(JSON).unwrap().map(|x| x.unwrap()).collect();
let key = Incline::new(4, 3);
let value = "a steep hill".to_owned();
let mut map: BTreeMap<Incline, String> = BTreeMap::new();
map.insert(key, value);
assert_eq!(deserialised, map);
}
}
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