在Serde中处理混合对象数组

Question

扩展我之前的问题,你如何处理包含混合的数组structs？我试过看serde_json::Value源头.但是它没有处理两种不同的情况structs.

我不能简单地合并它们,并且在它们的属性上使用Options,因为这会使单个struct变得难以处理,并且它们必须是不同的.

锈结构

#[derive(Clone, Debug, Deserialize)]
struct WebResponse {
    foo: Vec<Structs>,
}

enum Structs {
    Foo(Foo),
    Bar(Bar),
}

#[derive(Clone, Debug, Deserialize)]
struct Foo {
    name: String,
    baz: Vec<String>,
}

#[derive(Clone, Debug, Deserialize)]
struct Bar {
    quux: u64
}

示例JSON

{
    "foo": [
        {
            "name": "John",
            "baz": ["Lorem", "Ipsum"]
        },
        {
            "quux": 17
        }
    ]
}

Answer 1

有几种方法可以解决这个问题.如果你有几个变种,最简单的方法是简单地Deserialize手动实现,如下所示:

impl serde::de::Deserialize for Structs {
    fn deserialize<D>(deserializer: &mut D) -> Result<Self, D::Error>
        where D: serde::Deserializer,
    {
        deserializer.deserialize(Visitor)
    }
}

struct Visitor;

impl serde::de::Visitor for Visitor {
    type Value = Structs;

    fn visit_map<V>(&mut self, mut visitor: V) -> Result<Structs, V::Error>
        where V: serde::de::MapVisitor,
    {
        let s: String = try!(visitor.visit_key()).expect("got struct with no fields");
        let val = match &s as &str {
            "name" => {
                Ok(Structs::Foo(Foo {
                    name: try!(visitor.visit_value()),
                    baz: {
                        let s: String = try!(visitor.visit_key()).expect("baz field");
                        assert_eq!(&s, "baz");
                        try!(visitor.visit_value())
                    },
                }))
            },
            "baz" => {
                Ok(Structs::Foo(Foo {
                    baz: try!(visitor.visit_value()),
                    name: {
                        let s: String = try!(visitor.visit_key()).expect("name field");
                        assert_eq!(&s, "name");
                        try!(visitor.visit_value())
                    },
                }))
            },
            "quux" => {
                Ok(Structs::Bar(Bar {
                    quux: try!(visitor.visit_value())
                }))
            },
            other => panic!("no struct has field `{}`", other),
        };
        try!(visitor.end());
        val
    }
}

这种实现的问题在于它显然不能扩展.你可以做的是创建一个新的Deserializer,你给出第一个找到的字段名称,并覆盖deserialize_map通过自定义处理各种结构的方法MapVisitor.

如果您认为这是其他序列化框架支持的常见情况,请随时在serde存储库或serde-json存储库上发布错误报告.我确信有一种方法可以自动生成这样的实现,但这肯定不是微不足道的.