如何使用动态/任意字段在 golang 中创建结构/模型

Question

Is it possible to create a struct with dynamic/arbitrary fields and values?

My app will receive request with JSON body:

{
"Details": {
  "Id": “123”,
 },
"Event": {
  "Event": "Event",
 },
“RequestValues”: [
  {
    “Name": "Name1",
    "Value": "Val1"
  },
  {
    "Name": "Name2",
    "Value": 2
  },
  {
    "Name": “Foo”,
    "Value": true
  }
    ]
  }

This will be unmarshalled to my model 'Request':

type Request struct {
    Details         Details          `json:"Details"`
    Event           Event            `json:"Event"`
    RequestValues []RequestValues    `json:"RequestValues"`
}

type Details struct {
    Id     string `json:"Id"`
}

type Event struct {
    Event      string `json:"Event"`
}

type RequestValues struct {
    Name  string `json:"Name"`
    Value string `json:"Value"`
}

I have to re-map model 'Request' to a new model 'Event' with arbitrary fields in "Values". After marshalling new re- mapped model 'Event' I should get this JSON output that corresponds to the request:

{
"Event": "Event"
"Values": {
  “Id": "123",      <= non arbitrary mapping from Request.Detail.Id
  "Name1": "Val1",  <= arbitrary 
  "Name2": 2,       <= arbitrary
  “Foo”: true       <= arbitrary
}

}

Arbitrary values will be mapped from "RequestValues". Names of those fields should be the values of Request.RequestValues.Name and their values should be the values of Request.RequestValues.Value

Here is my 'Event' model:

type Event struct {
    Event             string `json:"Event"`
    Values            Values `json:"Values"`
}

type Values struct{
    Id      string  `json:"Id"`
}

Answer 1

Firstly, here's a JSON-valid copy of your JSON:

{
    "Details": {
        "Id": "123"
    },
    "Event": {
        "Event": "Event"
    },
    "RequestValues": [
        {
            "RequestValueName": "Name1",
            "RequestValue": "Val1"
        },
        {
            "RequestValueName": "Name2",
            "RequestValue": 2
        },
        {
            "RequestValueName": "Foo",
            "RequestValue": true
        }
    ]
}

Start by creating a type Input struct{} to describe the JSON that you're looking to parse, and a type Output struct{} for the JSON that you're looking to generate, and write a little code to convert from one to the other. You don't have to add all of the fields right away - you can start with just Event for example and add more until you've got them all.

I've done this in https://play.golang.org/p/PvpKnFMrJjN to show you, but I would recommend having only a quick read of it before trying to recreate it yourself.

A useful tool to convert JSON into Go structs is https://mholt.github.io/json-to-go/ but it will trip on RequestValue in your example which has several data types (and is therefore where we use interface{} ).

Answer 2

I thing that you can use map like this:

package main

import (
    "fmt"
)

type Event struct {
    event  string
    values map[string]string
}

func main() {
    eventVar := Event{event: "event", values: map[string]string{}}
    eventVar.values["Id"] = "12345"
    eventVar.values["vale1"] = "value"
    fmt.Println(eventVar)
}

You just need to validate somehow that the id it's in there, this if you need values in the same level.

I hope this works for you.