我正在处理遗留系统,该系统返回带有嵌套结构和一些可选字段的JSON(并且以随机顺序)。像这样:
type A struct {
/* simple struct, can be unmarshalled normally */
AF1 string `json:"AF1"`
}
type B struct {
/* simple struct, can be unmarshalled normally */
BF1 string `json:"BF1"`
}
type X struct {
Things []A `json:"things"` /* mandatory */
Thangs []B `json:"thangs"` /* mandatory */
/* some individual string values may or may not appear, eg:
Item1 string
Item2 string
*/
}
如果出现项目[12],我想将它们藏在地图或类似地方。
是否有任何优雅的解组X方式?有没有办法为X编写自定义UnmarshalJSON函数(处理选项字符串字段),然后切换到A和B的默认JSON unmarshaller?
答案 0 :(得分:0)
根据json.Unmarshal(...)
中的JSON对象类型将Items1 / 2声明为map[string]interface{}
。如果它们丢失,则只需将其设置为nil
:
type X struct {
// ...
Item1 string map[string]interface{}
Item2 string map[string]interface{}
另请注意,如果字段名称与JSON密钥名称匹配(不区分大小写),则无需为其包含json:"..."
名称标记。
type A struct {
AF1 string // Will look for keys named "AF1", "af1", etc.
}
答案 1 :(得分:0)
如果我从您的其他评论中正确理解了问题,
然后输入可能包含任何任意名称未知的额外字段(和类型?)
你想要/需要访问这些。
如果它只是为了以后的重新编组,那么json.RawMessage
类型会引起人们的兴趣。
理想情况下,encoding/json
会有一个特殊标记
(例如",any"
encoding/xml
标记
这将自动收集任何额外/未引用的JSON项目到a
map[string]interface{}
或map[string]json.RawMessage
字段。
但是,我找不到任何这样的功能,也没有找到一种用匿名结构模拟它的明显方法(但我并没有非常努力)。
编辑:有an open issue in the Go project for this feature。显然,在Go 1.2中提交了一项变更并进行了部分审核,但最终没有被接受。
如果做不到这一点,有几种方法可以完全按照你的建议去做,
为X创建自定义(un)marshaller并回调到json包中以处理[]A
和[]B
。
这是一个快速拼凑的例子, 可能有更好/更清晰/更安全的方法来做到这一点。 (在这个例子中,A和B可以是任意复杂的,可能包含自己有自定义(非)编组方法的类型。)
package main
import (
"encoding/json"
"fmt"
)
type A struct {
AF1 string
}
type B struct {
BF1 string
}
type X struct {
Things []A
Thangs []B
// Or perhaps json.RawMessage if you just
// want to pass them through.
// Or map of string/int/etc if the value type is fixed.
Extra map[string]interface{}
}
// Marshal Way 1: call unmarshal twice on whole input
type xsub struct {
Things []A `json:"things"`
Thangs []B `json:"thangs"`
}
func (x *X) _UnmarshalJSON(b []byte) error {
// First unmarshall the known keys part:
var tmp xsub
if err := json.Unmarshal(b, &tmp); err != nil {
return err
}
// Then unmarshall the whole thing again:
var vals map[string]interface{}
if err := json.Unmarshal(b, &vals); err != nil {
return err
}
// Everything worked, chuck the map entries for
// "known" fields and store results.
delete(vals, "things")
delete(vals, "thangs")
x.Things = tmp.Things
x.Thangs = tmp.Thangs
x.Extra = vals
return nil
}
// Way 2:
func (x *X) UnmarshalJSON(b []byte) error {
// Only partially decode:
var tmp map[string]json.RawMessage
if err := json.Unmarshal(b, &tmp); err != nil {
return err
}
// Now handle the known fields:
var things []A
if err := json.Unmarshal(tmp["things"], &things); err != nil {
return err
}
var thangs []B
if err := json.Unmarshal(tmp["thangs"], &thangs); err != nil {
return err
}
// And the unknown fields.
var extra map[string]interface{}
// Either:
if true {
// this has more calls to Unmarshal, but may be more desirable
// as it completely skips over the already handled things/thangs.
delete(tmp, "things")
delete(tmp, "thangs")
// If you only needed to store the json.RawMessage for use
// in MarshalJSON then you'd just store "tmp" and stop here.
extra = make(map[string]interface{}, len(tmp))
for k, raw := range tmp {
var v interface{}
if err := json.Unmarshal(raw, &v); err != nil {
return err
}
extra[k] = v
}
} else { // Or:
// just one more call to Unmarshal, but it will waste
// time with things/thangs again.
if err := json.Unmarshal(b, &extra); err != nil {
return err
}
delete(extra, "things")
delete(extra, "thangs")
}
// no error, we can store the results
x.Things = things
x.Thangs = thangs
x.Extra = extra
return nil
}
func (x X) MarshalJSON() ([]byte, error) {
// abusing/reusing x.Extra, could copy map instead
x.Extra["things"] = x.Things
x.Extra["thangs"] = x.Thangs
result, err := json.Marshal(x.Extra)
delete(x.Extra, "things")
delete(x.Extra, "thangs")
return result, err
}
func main() {
inputs := []string{
`{"things": [], "thangs": []}`,
`
{
"things": [
{
"AF1": "foo"
},
{
"AF1": "bar"
}
],
"thangs": [
{
"BF1": "string value"
}
],
"xRandomKey": "not known ahead of time",
"xAreValueTypesKnown": 172
}`,
}
for _, in := range inputs {
fmt.Printf("\nUnmarshal(%q):\n", in)
var x X
err := json.Unmarshal([]byte(in), &x)
if err != nil {
fmt.Println("unmarshal:", err)
} else {
fmt.Printf("\tas X: %+v\n", x)
fmt.Printf("\twith map: %v\n", x.Extra)
out, err := json.Marshal(x)
if err != nil {
fmt.Println("marshal:", err)
continue
}
fmt.Printf("\tRemarshals to: %s\n", out)
}
}
}
答案 2 :(得分:0)
作为Dace C答案的附加答案。 我想实现与您相同的目的,但是我想重用该函数,而不是对值进行硬编码。
这就是我做的:
type DynamicFieldsUnmarshaller interface {
WithExtraFields(map[string]interface{})
Unmarshal([]byte) error
}
type TestObject struct {
Name string `json:"name"`
CustomFields map[string]interface{} `json:"-"`
}
func (o *TestObject) Unmarshal(data []byte) error {
return UnmarshalCustomJSON(data,o)
}
func (o *TestObject) WithExtraFields(f map[string]interface{}) {
o.CustomFields = f
}
func UnmarshalCustomJSON(b []byte, o DynamicFieldsUnmarshaller) error {
if err := json.Unmarshal(b, &o); err != nil {
return err
}
// unmarshal everything to a map
var vals map[string]interface{}
if err := json.Unmarshal(b, &vals); err != nil {
return err
}
if len(vals)== 0 {
return nil
}
fields := reflect.TypeOf(o).Elem()
num := fields.NumField()
for i := 0; i < num; i++ {
field := fields.Field(i)
jsonTag := field.Tag.Get("json")
if jsonTag != "" && jsonTag != "-" {
delete(vals, jsonTag)
}
}
o.WithExtraFields(vals)
return nil
}
这只能将不在结构中的值添加到map[string]interface{}
字段中。
例如:
body := []byte(`
{
"name":"kilise",
"age": 40
}
`)
var dto TestObject
err := dto.Unmarshal(body)
if err != nil {
panic(err)
}
只会在dto.CustomFields映射中添加“年龄”。
请注意,此解决方案可能并不总是最好的,因为它没有实现json.Unmarshaler