如何动态获取结构中的字段

Question

I have the below struct. I have the method csv which will return concatenate the fields in a string with comma separated value.

package main

import (
    "bytes"
    "strconv"
)

type Event struct {
    B_id string
    B_nam string
    B_typ int
    B_uuid string
    B_mj_id int
    B_mi_id int
    B_uid string
    B_url string
    B_mac string
    E_typ string
    E_time string
    C_id string
    D_os string
    D_os_v string
    D_nam string
    D_v string
    Br_nam string
    Br_v string
    A_pkg string
    A_id string
    M_u_id string
    bn_id string
}

func (e *Event) Csv() string {
    var buffer bytes.Buffer
    var comma string = ","

    buffer.WriteString(e.B_id)
    buffer.WriteString(comma)
    buffer.WriteString(e.B_nam)
    buffer.WriteString(comma)
    buffer.WriteString(strconv.Itoa(e.B_typ))
    buffer.WriteString(comma)
    buffer.WriteString(e.B_uuid)
    buffer.WriteString(comma)
    buffer.WriteString(strconv.Itoa(e.B_mj_id))
    buffer.WriteString(comma)
    buffer.WriteString(strconv.Itoa(e.B_mi_id))
    buffer.WriteString(comma)
    buffer.WriteString(e.B_uid)
    buffer.WriteString(comma)
    buffer.WriteString(e.B_url)
    buffer.WriteString(comma)
    buffer.WriteString(e.B_mac)
    buffer.WriteString(comma)
    buffer.WriteString(e.E_typ)
    buffer.WriteString(comma)
    buffer.WriteString(e.E_time)
    buffer.WriteString(comma)
    buffer.WriteString(e.C_id)
    buffer.WriteString(comma)
    buffer.WriteString(e.D_os)
    buffer.WriteString(comma)
    buffer.WriteString(e.D_os_v)
    buffer.WriteString(comma)
    buffer.WriteString(e.D_nam)
    buffer.WriteString(comma)
    buffer.WriteString(e.D_v)
    buffer.WriteString(comma)
    buffer.WriteString(e.Br_nam)
    buffer.WriteString(comma)
    buffer.WriteString(e.Br_v)
    buffer.WriteString(comma)
    buffer.WriteString(e.A_pkg)
    buffer.WriteString(comma)
    buffer.WriteString(e.A_id)
    buffer.WriteString(comma)
    buffer.WriteString(e.M_u_id)
    buffer.WriteString(comma)
    buffer.WriteString(e.bn_id)

    return buffer.String()
}

Here you can see that I adding each fields in a buffer and returning it as a string. This code does not looks nice.

Is it possible to get the field value dynamically? Something like,

func (e *Event) Csv() string {
    var buffer bytes.Buffer
    var comma string = ","

    var x [22]string fieldValues = //Somehow get the field Values
    for i := 0; i < 22; i++ {
      buffer.WriteString(B_id)
      buffer.WriteString(comma)
    }

    return buffer.String()
}

Answer 1

Use reflect to iterate the struct fields.

Here is the example:

package main

import (
    "fmt"
    "reflect"
    "strings"
)

type Event struct {
    B_id    string
    B_nam   string
    B_typ   string
    B_uuid  string
    B_mj_id string
    B_mi_id string
    B_uid   string
    B_url   string
    B_mac   string
    E_typ   string
    E_time  string
    C_id    string
    D_os    string
    D_os_v  string
    D_nam   string
    D_v     string
    Br_nam  string
    Br_v    string
    A_pkg   string
    A_id    string
    M_u_id  string
    // bn_id   string  //FIXME: unexported fields not work for reflection?
}

func main() {
    // initialize your struct, I only take a few of fields as example.
    e := Event{A_id: "hah", M_u_id: "dadas"}
    v := reflect.ValueOf(e)

    values := make([]string, v.NumField())
    for i := 0; i < v.NumField(); i++ {
        values[i] = v.Field(i).String()
    }

    fmt.Println(strings.Join(values, ","))
}

May this be helpful.

You can run it online: http://play.golang.org/p/ZheOnMFRnI