解析嵌套的 JSON 对象

Question

我正在尝试使用 Rust 中的 serde_json 解析具有以下松散格式的 JSON 文件：

{
  "Source_n": {
    "Destination_n": {
      "distance": 2,
      "connections": [
        {
          "color": "Any",
          "locomotives": 0,
          "tunnels": 0
        }
      ]
    }
...

其中 Source 和 Destination 可以是任意数量的键 (Link to full file)。

我创建了以下结构，试图反序列化 JSON：

#[derive(Debug, Deserialize)]
struct L0 {
    routes: HashMap<String, L1>,
}

#[derive(Debug, Deserialize)]
struct L1 {
    destination_city: HashMap<String, L2>,
}

#[derive(Debug, Deserialize)]
struct L2 {
    distance: u8,
    connections: Vec<L3>,
}

#[derive(Debug, Deserialize, Clone)]
struct L3 {
    color: String,
    locomotives: u8,
    tunnels: u8,
}

当我尝试将 JSON 读取为 L0 对象时，我在这一行出现了恐慌：

let data: L0 = serde_json::from_str(&route_file_as_string).unwrap();

恐慌：

    Finished dev [unoptimized + debuginfo] target(s) in 0.01s
     Running `target/debug/ticket-to-ride`
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error("missing field `routes`", line: 1889, column: 1)', src/route.rs:39:64
stack backtrace:
   0: rust_begin_unwind
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/std/src/panicking.rs:517:5
   1: core::panicking::panic_fmt
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/core/src/panicking.rs:101:14
   2: core::result::unwrap_failed
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/core/src/result.rs:1617:5
   3: core::result::Result<T,E>::unwrap
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/core/src/result.rs:1299:23
   4: ticket_to_ride::route::route_file_to_L0
             at ./src/route.rs:39:20
   5: ticket_to_ride::route::routes_from_file
             at ./src/route.rs:44:33
   6: ticket_to_ride::main
             at ./src/main.rs:6:5
   7: core::ops::function::FnOnce::call_once
             at /rustc/59eed8a2aac0230a8b53e89d4e99d55912ba6b35/library/core/src/ops/function.rs:227:5

我已经能够将 JSON 读取为 HashMap<String, Value> 对象，但每当我尝试开始在较低级别工作时，我都会收到错误消息。它似乎在寻找一个名为 routes 的键，但我实际上想要的只是一个嵌套的 HashMap，类似于您如何以嵌套方式在 Python 中读取 JSON。

关于如何进行的任何建议？我对这个库的尝试合理吗？

Answer 1

正如 Sven Marnach 在他们的评论中所说，添加 #[serde(flatten)] 以从使用键作为 JSON 字段的数据创建 HashMap：

#[derive(Debug, Deserialize)]
struct L0 {
    #[serde(flatten)]
    routes: HashMap<String, L1>,
}

#[derive(Debug, Deserialize)]
struct L1 {
    #[serde(flatten)]
    destination_city: HashMap<String, L2>,
}

Answer 2

解析引用 JSON 的功能代码如下。 demo 函数执行解析。

use serde::Deserialize;
use std::collections::HashMap;
use std::fs;
use std::clone::Clone;

#[derive(Debug, Deserialize)]
pub struct L1 {
    #[serde(flatten)]
    destination_city: HashMap<String, L2>,
}

#[derive(Debug, Deserialize)]
struct L2 {
    distance: u8,
    connections: Vec<L3>,
}

#[derive(Debug, Deserialize, Clone)]
struct L3 {
    color: String,
    locomotives: u8,
    tunnels: u8,
}

fn route_file_to_hashmap(fpath: &str) -> HashMap<String, L1>  {
    let route_file_as_string = fs::read_to_string(fpath).expect("Unable to read file");
    let data: HashMap<String, L1> = serde_json::from_str(&route_file_as_string).unwrap();
    return data;
}

pub fn routes_from_file(fpath: &str) -> HashMap<String, L1>  {
    let route_file_as_map: HashMap<String, L1> = route_file_to_hashmap(fpath);
    return route_file_as_map;
}


pub fn demo() {
    let routes: HashMap<String, L1>  = routes_from_file("usa.routes.json");
    println!("---Cities---");
    for (k, _) in &routes {
        println!("{}", k);
    }
    let chicago: &HashMap<String, L2> = &routes.get("Chicago").unwrap().destination_city;
    println!("---Destinations from Chicago---");
    for (k, _) in chicago {
        println!("{}", k);
    }
    let to_omaha: &L2 = chicago.get("Omaha").unwrap();
    println!("---Data on Route to Omaha---");
    println!("Distance: {}", to_omaha.distance);
    print!("Connections: ");
    for c in &to_omaha.connections {
        println!("{} ", c.color);
    }
}

解析嵌套的 JSON 对象

Parsing a nested JSON object

json

rust

serde-json