将数据从一个 golang slice struct 复制到另一个 slice strcut

Question

Hi I have json data which I Unmarshal to machines slice. Now I am looking to copy/append each hostname from machines slice struct to service Struct []hosts. I have tried few methods but struggling to iterate over []hosts slice in service struct.

Just wondering what is the best way to copy the value from one slice struct to another slice value inside some other struct.

package main

import (
    "encoding/json"
    "fmt"
)

type Machine struct {
    hostname  string
    Ip   string
    Name string
}

type Host struct {
    HostName string `json:"host_name"`
    Vars Var `json:"vars"`
}

type Service struct {
    ServiceName string `json:"service_name"`
    Required    bool   `json:"required"`
    Hosts       []Host `json:"hosts"`
    Vars        Var    `json:"vars"`
}


func main() {
    machineInfo := `[{"dns":"1.1.1.1.eu-south-1.compute.amazonaws.com","ip":"1.1.1.1","name":"Machine-1"},{"dns":"1.1.1.2.eu-south-1.compute.amazonaws.com","ip":"1.1.1.2","name":"Machine-2"}]`

    var machines []Machine
    var mService *Service
    //convert the json to byts slice and then

    json.Unmarshal([]byte(machineInfo), &machines)

    //Data is now add to the structs



    for i, _ := range machines {
        mService.Hosts = append(mService.Hosts, machines[i].hostname)
    }
    fmt.Printf("Machines : %v", mService)
    
    data, _ := json.Marshal(mService)


    fmt.Println(string(data))
}

Answer 1

Let's take it from the top:

Export the hostname field by capitalizing it. The JSON decoder ignores unexpected fields. Also, add a tag so the field matches the document:

type Machine struct {
    Hostname string `json:"name"`
    Ip       string
    Name     string
}

Declare mServices as a value to avoid nil pointer panic:

var mService Service

Use a composite literal expression to create a host for append to the slice:

    mService.Hosts = append(mService.Hosts, Host{HostName: machines[i].Hostname})

https://go.dev/play/p/nTBVwM3l9Iw