web-dev-qa-db-ja.com

ネストされたJSON構造をSerdeで逆シリアル化する場合、「無効なタイプ：マップ、シーケンスが必要です」

GitHub APIに問題がないかポーリングして、印刷しようとしています。そのためには、cURLGETリクエストから受け取ったネストされたJSON構造を逆シリアル化する必要があります。

url配列内のすべてのオブジェクトのitemsを取得しようとしています。

{
 "total_count": 4905,
 "incomplete_results": false,
 "items": [
    {
     "url": "https://api.github.com/repos/servo/saltfs/issues/789",
     "repository_url": "https://api.github.com/repos/servo/saltfs",
     "labels_url": 
   "https://api.github.com/repos/servo/saltfs/issues/789/labels{/name}",
  "comments_url": "https://api.github.com/repos/servo/saltfs/issues/789/comments",
  "events_url": "https://api.github.com/repos/servo/saltfs/issues/789/events",
  "html_url": "https://github.com/servo/saltfs/issues/789",
  "id": 293260512,
  "number": 789,
  "title": "Stop setting $CARGO_HOME to its default value",
  "user": {
    "login": "SimonSapin",
    "id": 291359,
    "avatar_url": "https://avatars0.githubusercontent.com/u/291359?v=4",
    "gravatar_id": "",
    "url": "https://api.github.com/users/SimonSapin",
    "html_url": "https://github.com/SimonSapin",
    "followers_url": "https://api.github.com/users/SimonSapin/followers",
    "following_url": "https://api.github.com/users/SimonSapin/following{/other_user}",
    "gists_url": "https://api.github.com/users/SimonSapin/gists{/Gist_id}",
    "starred_url": "https://api.github.com/users/SimonSapin/starred{/owner}{/repo}",
    "subscriptions_url": "https://api.github.com/users/SimonSapin/subscriptions",
    "organizations_url": "https://api.github.com/users/SimonSapin/orgs",
    "repos_url": "https://api.github.com/users/SimonSapin/repos",
    "events_url": "https://api.github.com/users/SimonSapin/events{/privacy}",
    "received_events_url": "https://api.github.com/users/SimonSapin/received_events",
    "type": "User",
    "site_admin": false
  },
  "labels": [
    {
      "id": 341722396,
      "url": "https://api.github.com/repos/servo/saltfs/labels/E-easy",
      "name": "E-easy",
      "color": "02e10c",
      "default": false
    }
  ],
  "state": "open",
  "locked": false,
  "assignee": null,
  "assignees": [

  ],
  "milestone": null,
  "comments": 0,
  "created_at": "2018-01-31T18:16:09Z",
  "updated_at": "2018-01-31T18:16:49Z",
  "closed_at": null,
  "author_association": "MEMBER",
  "body": "In `buildbot/master/files/config/environments.py` we set `CARGO_HOME` to Cargo’s default value. Now that `mach` does not set it (since https://github.com/servo/servo/pull/19395), this has no effect. We can remove these lines.",
  "score": 1.0
},
{
  "url": "https://api.github.com/repos/servo/servo/issues/19916",
  "repository_url": "https://api.github.com/repos/servo/servo",
  "labels_url": "https://api.github.com/repos/servo/servo/issues/19916/labels{/name}",
  "comments_url": "https://api.github.com/repos/servo/servo/issues/19916/comments",
  "events_url": "https://api.github.com/repos/servo/servo/issues/19916/events",
  "html_url": "https://github.com/servo/servo/issues/19916",
  "id": 293237180,
  "number": 19916,
  "title": "Use a macro to create null-terminated C strings",
  "user": {
    "login": "jdm",
    "id": 27658,
    "avatar_url": "https://avatars1.githubusercontent.com/u/27658?v=4",
    "gravatar_id": "",
    "url": "https://api.github.com/users/jdm",
    "html_url": "https://github.com/jdm",
    "followers_url": "https://api.github.com/users/jdm/followers",
    "following_url": "https://api.github.com/users/jdm/following{/other_user}",
    "gists_url": "https://api.github.com/users/jdm/gists{/Gist_id}",
    "starred_url": "https://api.github.com/users/jdm/starred{/owner}{/repo}",
    "subscriptions_url": "https://api.github.com/users/jdm/subscriptions",
    "organizations_url": "https://api.github.com/users/jdm/orgs",
    "repos_url": "https://api.github.com/users/jdm/repos",
    "events_url": "https://api.github.com/users/jdm/events{/privacy}",
    "received_events_url": "https://api.github.com/users/jdm/received_events",
    "type": "User",
    "site_admin": false
  },
  "labels": [
    {
      "id": 89384911,
      "url": "https://api.github.com/repos/servo/servo/labels/C-assigned",
      "name": "C-assigned",
      "color": "02d7e1",
      "default": false
    },
    {
      "id": 15997664,
      "url": "https://api.github.com/repos/servo/servo/labels/E-easy",
      "name": "E-easy",
      "color": "02e10c",
      "default": false
    },
    {
      "id": 135307111,
      "url": "https://api.github.com/repos/servo/servo/labels/I-cleanup",
      "name": "I-cleanup",
      "color": "e11d21",
      "default": false
    }
  ],
  "state": "open",
  "locked": false,
  "assignee": null,
  "assignees": [

  ],
  "milestone": null,
  "comments": 3,
  "created_at": "2018-01-31T17:04:06Z",
  "updated_at": "2018-01-31T22:03:56Z",
  "closed_at": null,
  "author_association": "MEMBER",
  "body": "When we write them by hand (eg. `b\"some string\\0\"`), we invariably get them wrong in ways that are tricky to notice (https://github.com/servo/servo/pull/19915). We should use a macro like this instead:\r\n```Rust\r\nmacro_rules! c_str {\r\n    ($str:expr) => {\r\n        concat!($str, \"\\0\").as_bytes()\r\n    }\r\n}\r\n```\r\nThis would allow us to write code like `(c_str!(\"PEParseDeclarationDeclExpected\"), Action::Skip)` instead of https://github.com/emilio/servo/blob/d82c54bd3033cc3277ebeb4854739bebe4e20f2f/ports/geckolib/error_reporter.rs#L237. We should be able to clean up all of the uses in that file.\r\n\r\nNo need to run any automated tests; if it builds with `./mach build-geckolib`, then it's good enough for a pull request.",
  "score": 1.0
}
]}

私のrequest関数はcURLリクエストを作成し、上記のJSONを受信します。次に、serde_jsonを使用してJSONを逆シリアル化します

main.rs

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

mod engine;
mod server;
use engine::request;
use std::string::String;
use self::serde_json::{Error, Value};

#[derive(Serialize, Deserialize)]
struct obj {
    items: Vec<String>,
}

fn main() {
    let output_jn: String = request(
        "https://api.github.com/search/issues?q=is:issue+label:e-easy",
    ).to_string(); //gets json structure as string
    let json: obj = serde_json::from_str(&output_jn).unwrap();

    for elem in json.iter() {
        println!("{:?}", elem);
    }
}

次のエラーメッセージが表示されます

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: 
ErrorImpl { code: Message("invalid type: map, expected a sequence"), 
line: 1, column: 0 }', libcore/result.rs:945:5
note: Run with `Rust_BACKTRACE=1` for a backtrace.

JSON構造を逆シリアル化する際に愚かな間違いを犯していると確信しています。いくつかの順列と組み合わせを試しましたが、何も機能しませんでした。

jsonserializationrustserdeserde-json
7
zep

JSON入力データのこの部分を見てください。

{
  ...
  "items": [
    {
      ...
      "title": "Stop setting $CARGO_HOME to its default value",
      ...
    }
  ]
}
  • 最上位のデータ構造はJSONマップであるため、Rustでは、これは構造体として表されます。名前はObjを使用します。
  • トップレベルのJSONマップには"items"というキーがあるため、Rustこれはitems構造体内のフィールドObjになります。
  • マップ内の"items"の値はJSON配列であるため、Rustでは、Vecを使用しましょう。
  • JSON配列の各要素はJSONマップであるため、Rustでは、それらの構造体が必要です。これをIssueと呼ぶことができます。
  • 各号には"title"というJSONキーがあるため、これはtitle構造体内のフィールドIssueになります。
  • "title"の値はJSON文字列であるため、フィールドにRustのString型を使用できます。
#[derive(Deserialize, Debug)]
struct Obj {
    items: Vec<Issue>,
}

#[derive(Deserialize, Debug)]
struct Issue {
    title: String,
}

fn main() {
    let j = /* get the JSON data */;

    let issues = serde_json::from_str::<Obj>(j).unwrap();
    for i in issues.items {
        println!("{:#?}", i);
    }
}
8
dtolnay