如何更改 Golang Struct 值的位置？

Question

How would I change the position of the json values?

What Im trying to achieve:

[{"key":"f","value":"f"},{"value":"f","key":"f"}]

Problem:

type Struct struct {
    Key   string `json:"key"`
    Value string `json:"value"`
}

func main() {
    test := []Struct{ {Key: "test",Value: "wep"}, {Value: "wep",Key: "test"}}


    bytes, _ := json.Marshal(test)
    fmt.Print(string(bytes))
}

Running this code prints [{"key":"test","value":"wep"},{"key":"test","value":"wep"}]

I have also tried doing something like this but it just printed empty values

type Struct struct {
    Key   string `json:"key"`
    Value string `json:"value"`
    Value2 string `json:"value"`
    Key2   string `json:"key"`
}

But how would I be able to switch the position of the key and value field around?

Answer 1

To the question "can I make a single struct type serialize its fields in a different order or different occasions ?" :
there isn't a simple way to do this.

Regarding struct fields : the code you write shows the assigning operations in a given order, but once your code is compiled, there is no trace of that order anymore.

If you really need this (side note : I would be curious to know about your use case ?), you could create a custom type, with its own .MarshalJSON() method, which would hold a value indicating "fields should be serialized in this order".

---

If what you need is to send an array of heterogeneous objects, use separate struct types, and an []interface{} array :

type Obj1 struct{
    Key string `json:"name"`
    Value string `json:"value"`
}

type Obj2 struct{
    Value string `json:"value"`
    Key string `json:"name"`
}

func main() {
    test := []interface{}{ Obj1{Key: "test",Value: "wep"}, Obj2{Value: "wep",Key: "test"}}


    bytes, _ := json.Marshal(test)
    fmt.Print(string(bytes))
}

https://play.golang.org/p/TOk28gL0eSK

Answer 2

If you're using json.Marshal provided by official package it's not passible to do that. In stead, you can implement your own MarhalJSON method so that you can decide the position of your struct fields.

Answer 3

type StructA struct {
    Key   string `json:"key"`
    Value string `json:"value"`
}

type StructB struct {
    Value string `json:"value"`
    Key   string `json:"key"`
}

func main() {
    test := []interface{}{
        StructA{Key: "test", Value: "wep"},
        StructB{Value: "wep", Key: "test"},
    }

    bytes, _ := json.Marshal(test)
    fmt.Print(string(bytes))
}

https://play.golang.org/p/72TWDU1BMaL