如何将两个 JSON 对象与 Rust 合并？

Question

我有两个 JSON 文件：

JSON 1

{
  "title": "This is a title",
  "person" : {
    "firstName" : "John",
    "lastName" : "Doe"
  },
  "cities":[ "london", "paris" ]
}

JSON 2

{
  "title": "This is another title",
  "person" : {
    "firstName" : "Jane"
  },
  "cities":[ "colombo" ]
}

我想将 #2 合并到 #1 中，其中 #2 覆盖 #1，产生以下输出：

{
  "title": "This is another title",
  "person" : {
    "firstName" : "Jane",
    "lastName" : "Doe"
  },
  "cities":[ "colombo" ]
}

我检查了板条箱 json-patch which does this but it does not compile against stable Rust. Is it possible to do something similar with something like serde_json 和稳定的 Rust？

Answer 1

这对我有用

#[macro_use]
extern crate serde_json;

use serde_json::Value;

fn merge(a: &mut Value, b: &Value) {
    match (a, b) {
        (&mut Value::Object(ref mut a), &Value::Object(ref b)) => {
            for (k, v) in b {
                merge(a.entry(k.clone()).or_insert(Value::Null), v);
            }
        }
        (a, b) => {
            *a = b.clone();
        }
    }
}

fn main() {
    let mut a = json!({
        "title": "This is a title",
        "person" : {
            "firstName" : "John",
            "lastName" : "Doe"
        },
        "cities":[ "london", "paris" ]
    });

    let b = json!({
        "title": "This is another title",
        "person" : {
            "firstName" : "Jane"
        },
        "cities":[ "colombo" ]
    });

    merge(&mut a, &b);
    println!("{:#}", a);
}

Answer 2

将 Shepmaster 建议的答案放在下面

#[macro_use]
extern crate serde_json;

use serde_json::Value;

fn merge(a: &mut Value, b: Value) {
    match (a, b) {
        (a @ &mut Value::Object(_), Value::Object(b)) => {
            let a = a.as_object_mut().unwrap();
            for (k, v) in b {
                merge(a.entry(k).or_insert(Value::Null), v);
            }
        }
        (a, b) => *a = b,
    }
}

fn main() {
    let mut a = json!({
        "title": "This is a title",
        "person" : {
            "firstName" : "John",
            "lastName" : "Doe"
        },
        "cities":[ "london", "paris" ]
    });

    let b = json!({
        "title": "This is another title",
        "person" : {
            "firstName" : "Jane"
        },
        "cities":[ "colombo" ]
    });

    merge(&mut a, b);
    println!("{:#}", a);
}

Answer 3

因为您想使用 json-patch, I assume you were looking specifically for a JSON Merge Patch (RFC 7396) 实现，因为那是那个 crate 实现的。在那种情况下，合并一个对象应该取消设置那些在补丁中对应值为 null 的键，其他答案中的代码示例没有实现。

说明这一点的代码如下。我修改了补丁以删除 person.lastName 键，将其设置为 null 作为演示。与其他答案之一不同，它也不需要 unwrap() as_object_mut() 返回的 Option。

use serde_json::{json, Value};

fn merge(a: &mut Value, b: Value) {
    if let Value::Object(a) = a {
        if let Value::Object(b) = b {
            for (k, v) in b {
                if v.is_null() {
                    a.remove(&k);
                }
                else {
                    merge(a.entry(k).or_insert(Value::Null), v);
                }
            } 

            return;
        }
    }

    *a = b;
}

fn main() {
    let mut a = json!({
        "title": "This is a title",
        "person" : {
            "firstName" : "John",
            "lastName" : "Doe"
        },
        "cities":[ "london", "paris" ]
    });

    let b = json!({
        "title": "This is another title",
        "person" : {
            "firstName" : "Jane",
            "lastName": null
        },
        "cities":[ "colombo" ]
    });

    merge(&mut a, b);
    println!("{:#}", a);
}

预期输出为

{
  "cities": [
    "colombo"
  ],
  "person": {
    "firstName": "Jane"
  },
  "title": "This is another title"
}

通知 person.lastName 已取消设置。

如何将两个 JSON 对象与 Rust 合并？

How can I merge two JSON objects with Rust?

json

rust

serde

json-patch

serde-json