JSON字段设置为null vs字段不存在 [英] JSON field set to null vs field not there

问题描述

在golang中，有没有一种方法可以查看是否可以将解编为结构的json字段与设置为null的json字段区分开?因为两者都将struct中的值设置为nil，但是我需要知道该字段是否以该字段开头，并查看是否有人将其设置为null.

Is there a way, in golang, to see if I can differentiate between a json field being set to null vs a json field not being there when unmarshalled into a struct? Because both set the value in the struct to be nil, but I need to know if the field was there to begin with and to see if someone set it to null.

{
  "somefield1":"somevalue1",
  "somefield2":null
}

VS

{
  "somefield1":"somevalue1",
}

两个jsons在解组为结构时都将为零. 任何有用的资源将不胜感激！

Both jsons will be nil when unmarshalled into a struct. Any useful resources will be very appreciated!

推荐答案

在决定做某事之前，使用json.RawMessage延迟"解编组过程以确定原始字节:

Use json.RawMessage to "delay" the unmarshaling process to determine the raw byte before deciding to do something:

var data = []byte(`{
        "somefield1":"somevalue1",
        "somefield2": null
}`)

type Data struct {
    SomeField1 string          
    SomeField2 json.RawMessage
}

func main() {
    d := &Data{}

    _ = json.Unmarshal(data, &d)

    fmt.Println(d.SomeField1)

    if len(d.SomeField2) > 0 {
        if string(d.SomeField2) == "null" {
            fmt.Println("somefield2 is there but null")
        } else {
            fmt.Println("somefield2 is there and not null")
            // Do something with the data
        }
    } else {
        fmt.Println("somefield2 doesn't exist")
    }
}

参观游乐场 https://play.golang.org/p/Wganpf4sbO

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