如果struct golang中的值是nil,0,false,则更新字段吗? [英] Update field if value is nil, 0, false in struct golang?
本文介绍了如果struct golang中的值是nil,0,false,则更新字段吗?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我有一个结构:
type User struct {
ID int `json:"id"`
Username string `json:"username"`
About string `json:"about"`
IsAdmin bool `json:"is_admin"`
Status int `json:"status"`
......
}
A:= User{1,"admin", "I am a admin",status: 1,....}
B:= User{ID:1, Username: "UserBBBB"}
...enter code here...
B is {1, "UserBBBB", "I am a admin", 1, ...(same value in A)}
对象B具有一些属性,分别为nil(字符串),false(布尔),0(整数),...我想检查B的字段是否为未分配值,该字段将接收A中相同字段的值,
object B has a few properties with nil (string), false (bool), 0 (int),... I want to check if a field of B is unassigned value, that field will receive value of the same field in A,
示例:
B的关于"字段为nil;
B's About field is nil;
A的关于"字段是我是管理员"我要B的关于"字段为我是管理员".
A's About field is "I am a admin" I want to B's About field is "I am a admin".
我可以写代码:
if len(B.About) == 0 {
B.About = A.About
}与其他字段类似,我不想逐步检查所有字段.
} Similar to other fields, I don't want check step by step with all of fields.
推荐答案
package main
import (
"errors"
"fmt"
"log"
"reflect"
"time"
)
type User struct {
ID int `json:"id"`
Username string `json:"username"`
About string `json:"about"`
IsAdmin bool `json:"is_admin"`
Status int `json:"status"`
Date *time.Time
}
func main() {
now := time.Now()
ua := User{
ID: 1,
Username: "admin",
About: "I am an admin",
IsAdmin: true,
Status: 1,
Date: &now,
}
ub := User{
Username: "user",
}
fmt.Printf("ua: %+v\n", ua)
fmt.Printf("ub: %+v\n", ub)
err := Replace(ua, &ub)
if err != nil {
log.Fatal(err)
}
fmt.Printf("\nua: %+v\n", ua)
fmt.Printf("ub: %+v\n", ub)
}
// IsZeroOfUnderlyingType return wether x is the is
// the zero-value of its underlying type.
func IsZeroOfUnderlyingType(x interface{}) bool {
return reflect.DeepEqual(x, reflect.Zero(reflect.TypeOf(x)).Interface())
}
// Replace replaces all fields of struct b that have a
// zero-value with the corresponding field value from a.
// b must be a pointer to a struct.
func Replace(a, b interface{}) error {
// Check a.
va := reflect.ValueOf(a)
if va.Kind() != reflect.Struct {
return errors.New("a is not a struct")
}
// Check b.
vb := reflect.ValueOf(b)
if vb.Kind() != reflect.Ptr {
return errors.New("b is not a pointer")
}
// vb is a pointer, indirect it to get the
// underlying value, and make sure it is a struct.
vb = vb.Elem()
if vb.Kind() != reflect.Struct {
return errors.New("b is not a struct")
}
for i := 0; i < vb.NumField(); i++ {
field := vb.Field(i)
if field.CanInterface() && IsZeroOfUnderlyingType(field.Interface()) {
// This field have a zero-value.
// Search in a for a field with the same name.
name := vb.Type().Field(i).Name
fa := va.FieldByName(name)
if fa.IsValid() {
// Field with name was found in struct a,
// assign its value to the field in b.
if field.CanSet() {
field.Set(fa)
}
}
}
}
return nil
}
输出
ua: {ID:1 Username:admin About:I am an admin IsAdmin:true Status:1 Date:2017-05-11 17:47:30.805657327 +0200 CEST}
ub: {ID:0 Username:user About: IsAdmin:false Status:0 Date:<nil>}
ua: {ID:1 Username:admin About:I am an admin IsAdmin:true Status:1 Date:2017-05-11 17:47:30.805657327 +0200 CEST}
ub: {ID:1 Username:user About:I am an admin IsAdmin:true Status:1 Date:2017-05-11 17:47:30.805657327 +0200 CEST}
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