golang 中判断结构体中某一个属性是否存在（以区分零值）

原问题地址：validate-struct field if it exists

有定义结构

package mainimport ("fmt""encoding/json"
)type User struct {Name     string  `json:"name,omitempty"`Username *string `json:"username,omitempty"`Email    string  `json:"email,omitempty"`Town     string  `json:"town,omitempty"`//more fields here
}func main() {var u, u2 Userjson.Unmarshal([]byte(`{"username":"hi"}`), &u)fmt.Println("username set:", u.Username != nil, *u.Username)json.Unmarshal([]byte(`{}`), &u2)fmt.Println("username set:", u2.Username != nil)fmt.Println("Hello, playground")
}

反射方式

import ("log""reflect"
)func main() {type test struct {A boolB boolC bool}v := new(test)metaValue := reflect.ValueOf(v).Elem()for _, name := range []string{"A", "C", "Z"} {field := metaValue.FieldByName(name)if field == (reflect.Value{}) {log.Printf("Field %s not exist in struct", name)}}
}

借助 json 库

package mainimport ("fmt""encoding/json"
)func main() {fmt.Println("Hello, World!")type Meta struct{FcTag struct{Name string `json:"name"`Value json.Number `json:"value"`} `json:"fc_tag"`}template := `{"fc_tag": {"name": "tiger"}}`var meta1 Metaerr := json.Unmarshal([]byte(template), &meta1)if err != nil {fmt.Println("err=", err.Error())}else{fmt.Printf("meta1=%#v\n", meta1.FcTag.Value)}template = `{"fc_tag": {"name": "tiger", "value": 1}}`var meta2 Metaerr2 := json.Unmarshal([]byte(template), &meta2)if err2 != nil {fmt.Println("err=", err2.Error())}else{fmt.Printf("meta2=%#v\n", meta2.FcTag.Value)}
}/*Hello, World!meta1=""meta2="1"
*/