我在Go中创建了一个API，在被调用时，执行查询，创建一个结构实例，然后在发送回调用者之前将该结构编码为JSON。现在，我想允许调用者通过传入“fields”GET参数来选择他们想要返回的特定字段。
这意味着根据字段的值，我的结构将会改变。是否有方法从结构中删除字段?或者至少动态地将它们隐藏在JSON响应中?(注:有时我有空值，所以JSON omitEmpty标签将不在这里工作)如果这些都不可能，有没有一个更好的方法来处理这个问题的建议?
下面是我正在使用的结构体的一个较小版本:
type SearchResult struct {
Date string `json:"date"`
IdCompany int `json:"idCompany"`
Company string `json:"company"`
IdIndustry interface{} `json:"idIndustry"`
Industry string `json:"industry"`
IdContinent interface{} `json:"idContinent"`
Continent string `json:"continent"`
IdCountry interface{} `json:"idCountry"`
Country string `json:"country"`
IdState interface{} `json:"idState"`
State string `json:"state"`
IdCity interface{} `json:"idCity"`
City string `json:"city"`
} //SearchResult
type SearchResults struct {
NumberResults int `json:"numberResults"`
Results []SearchResult `json:"results"`
} //type SearchResults
然后我编码并输出响应，就像这样:
err := json.NewEncoder(c.ResponseWriter).Encode(&msg)
为了扩展chhaileng的答案，这里有一个版本，删除所有出现的字段与递归
// GetJSONWithOutFields - Description: return a string representation of an interface with specified fields removed
func GetJSONWithOutFields(obj interface{}, ignoreFields ...string) (string, error) {
toJson, err := json.Marshal(obj)
if err != nil {
return "", err
}
if len(ignoreFields) == 0 {
return string(toJson), nil
}
toMap := map[string]interface{}{}
err = json.Unmarshal(toJson, &toMap)
if err != nil {
return "", err
}
for _, field := range ignoreFields {
DeleteField(toMap, field)
}
toJson, err = json.Marshal(toMap)
if err != nil {
return "", err
}
return string(toJson), nil
}
// DeleteField - Description: recursively delete field
func DeleteField(toMap map[string]interface{}, field string) {
delete(toMap, field)
for _, v := range toMap {
if m, isMap := v.(map[string]interface{}); isMap {
DeleteField(m, field)
}
}
}
为了扩展chhaileng的答案，这里有一个版本，删除所有出现的字段与递归
// GetJSONWithOutFields - Description: return a string representation of an interface with specified fields removed
func GetJSONWithOutFields(obj interface{}, ignoreFields ...string) (string, error) {
toJson, err := json.Marshal(obj)
if err != nil {
return "", err
}
if len(ignoreFields) == 0 {
return string(toJson), nil
}
toMap := map[string]interface{}{}
err = json.Unmarshal(toJson, &toMap)
if err != nil {
return "", err
}
for _, field := range ignoreFields {
DeleteField(toMap, field)
}
toJson, err = json.Marshal(toMap)
if err != nil {
return "", err
}
return string(toJson), nil
}
// DeleteField - Description: recursively delete field
func DeleteField(toMap map[string]interface{}, field string) {
delete(toMap, field)
for _, v := range toMap {
if m, isMap := v.(map[string]interface{}); isMap {
DeleteField(m, field)
}
}
}
我刚刚发布了sheriff，它将结构转换为基于结构字段上标注的标记的映射。然后可以编组(JSON或其他)生成的映射。它可能不允许您只序列化调用者请求的字段集，但我认为使用组集将允许您覆盖大多数情况。使用组而不是直接使用字段也很可能提高缓存能力。
例子:
package main
import (
"encoding/json"
"fmt"
"log"
"github.com/hashicorp/go-version"
"github.com/liip/sheriff"
)
type User struct {
Username string `json:"username" groups:"api"`
Email string `json:"email" groups:"personal"`
Name string `json:"name" groups:"api"`
Roles []string `json:"roles" groups:"api" since:"2"`
}
func main() {
user := User{
Username: "alice",
Email: "alice@example.org",
Name: "Alice",
Roles: []string{"user", "admin"},
}
v2, err := version.NewVersion("2.0.0")
if err != nil {
log.Panic(err)
}
o := &sheriff.Options{
Groups: []string{"api"},
ApiVersion: v2,
}
data, err := sheriff.Marshal(o, user)
if err != nil {
log.Panic(err)
}
output, err := json.MarshalIndent(data, "", " ")
if err != nil {
log.Panic(err)
}
fmt.Printf("%s", output)
}
I didn't have the same problem but similar. Below code solves your problem too, of course if you don't mind performance issue. Before implement that kind of solution to your system I recommend you to redesign your structure if you can. Sending variable structure response is over-engineering. I believe a response structure represents a contract between a request and resource and it should't be depend requests.(you can make un-wanted fields null, I do). In some cases we have to implement this design, if you believe you are in that cases here is the play link and code I use.
type User2 struct {
ID int `groups:"id" json:"id,omitempty"`
Username string `groups:"username" json:"username,omitempty"`
Nickname string `groups:"nickname" json:"nickname,omitempty"`
}
type User struct {
ID int `groups:"private,public" json:"id,omitempty"`
Username string `groups:"private" json:"username,omitempty"`
Nickname string `groups:"public" json:"nickname,omitempty"`
}
var (
tagName = "groups"
)
//OmitFields sets fields nil by checking their tag group value and access control tags(acTags)
func OmitFields(obj interface{}, acTags []string) {
//nilV := reflect.Value{}
sv := reflect.ValueOf(obj).Elem()
st := sv.Type()
if sv.Kind() == reflect.Struct {
for i := 0; i < st.NumField(); i++ {
fieldVal := sv.Field(i)
if fieldVal.CanSet() {
tagStr := st.Field(i).Tag.Get(tagName)
if len(tagStr) == 0 {
continue
}
tagList := strings.Split(strings.Replace(tagStr, " ", "", -1), ",")
//fmt.Println(tagList)
// ContainsCommonItem checks whether there is at least one common item in arrays
if !ContainsCommonItem(tagList, acTags) {
fieldVal.Set(reflect.Zero(fieldVal.Type()))
}
}
}
}
}
//ContainsCommonItem checks if arrays have at least one equal item
func ContainsCommonItem(arr1 []string, arr2 []string) bool {
for i := 0; i < len(arr1); i++ {
for j := 0; j < len(arr2); j++ {
if arr1[i] == arr2[j] {
return true
}
}
}
return false
}
func main() {
u := User{ID: 1, Username: "very secret", Nickname: "hinzir"}
//assume authenticated user doesn't has permission to access private fields
OmitFields(&u, []string{"public"})
bytes, _ := json.Marshal(&u)
fmt.Println(string(bytes))
u2 := User2{ID: 1, Username: "very secret", Nickname: "hinzir"}
//you want to filter fields by field names
OmitFields(&u2, []string{"id", "nickname"})
bytes, _ = json.Marshal(&u2)
fmt.Println(string(bytes))
}
