英文:
golang: "json: cannot unmarshal array into Go value of type string"
问题
我有一个 protobuf 消息：
message Event {
string type = 1;
string names = 2;
}
在底层数据源中，'names' 的类型最近从 string 改变为 []string，其中旧数据仍然是字符串，但新数据将是 []string。因此，当数据返回时，一些记录可能是字符串，而其他记录可能是 []string。为了保持响应格式的一致性，以防止客户端出错，我需要自定义解组（使用 jsonpb.Unmarshaler 将 json.Rawmessage 解组为 Event 类型），如果 'names' 是 []string，则将其转换为字符串（通过连接数组/切片中的值）。
在解组时，我遇到了以下错误：
json: 无法将数组解组为类型为 string 的 Go 值
请问有人可以提供关于如何解决这个问题的建议吗？
我尝试过使用 google.protobuf.Any，如下所示，但无法完全弄清楚解组部分：
message Event {
string type = 1;
google.protobuf.Any names = 2;
}
解组代码片段：
evnt := new(pb.Event)
unmarshaler := jsonpb.Unmarshaler{AllowUnknownFields: true}
unmarshaler.Unmarshal(bytes.NewReader(*<json.RawMessage>*), evnt)
英文:
I have a protobuf message
message Event {
string type = 1;
string names = 2;
}
The type for ‘names’ has recently changed from string to []string in the underlying data source where older data is still a string but new data is going to be []string.
So, when the data is returned, some records can have string and the rest can have []string.
I need to customize the unmarshaling (jsonpb.Unmarshaler is being used to unmarshal json.Rawmessage to Event type) and convert the ‘names’ to a string if it’s an []string (by concatenating the values from array/slice) in order to keep the response format consistent so client doesn't break.
I get this error while unmarshaling:
> json: cannot unmarshal array into Go value of type string
Can anyone please suggest on how this can be done?
I tried google.protobuf.Any like below but couldn’t completely figure the unmarshaling part.
message Event {
string type = 1;
google.protobuf.Any names = 2;
}
Unmarshall snippet:
evnt := new(pb.Event)
unmarshaler = jsonpb.Unmarshaler{AllowUnknownFields: true}
unmarshaler.Unmarshal(bytes.NewReader(*<json.RawMessage>*), evnt)
答案1
得分: 1
将名称转换为类型，然后给它一个自定义的UnmarshalJSON方法。示例：
package main
import (
"encoding/json"
"fmt"
"os"
"strings"
)
type name struct {
New []string
Old string
}
type event struct {
Type string `json:"type"`
Name name `json:"name"`
}
func do(j string) {
var e event
err := json.Unmarshal([]byte(j), &e)
if err != nil {
fmt.Fprintf(os.Stderr, "Failed to unmarshall %s: %s\n", j, err)
return
}
fmt.Printf("%v\n", e)
}
func (n *name) UnmarshalJSON(text []byte) error {
t := strings.TrimSpace(string(text))
if strings.HasPrefix(t, "[") {
return json.Unmarshal(text, &n.New)
}
return json.Unmarshal(text, &n.Old)
}
func main() {
jsonstring := `{"type":"a","name":"rodney"}`
jsonarray := `{"type":"a","name":["rodney","dangerfield"]}`
do(jsonstring)
do(jsonarray)
}
Playground: https://go.dev/play/p/sNtUZKHC_Rt
英文:
Make the name into a type then give it a custom UnmarshalJSON method. Example:
package main
import (
"encoding/json"
"fmt"
"os"
"strings"
)
type name struct {
New []string
Old string
}
type event struct {
Type string `json:"type"`
Name name `json:"name"`
}
func do(j string) {
var e event
err := json.Unmarshal([]byte(j), &e)
if err != nil {
fmt.Fprintf(os.Stderr, "Failed to unmarshall %s: %s\n", j, err)
return
}
fmt.Printf("%v\n", e)
}
func (n *name) UnmarshalJSON(text []byte) error {
t := strings.TrimSpace(string(text))
if strings.HasPrefix(t, "[") {
return json.Unmarshal(text, &n.New)
}
return json.Unmarshal(text, &n.Old)
}
func main() {
jsonstring := `{"type":"a","name":"rodney"}`
jsonarray := `{"type":"a","name":["rodney","dangerfield"]}`
do(jsonstring)
do(jsonarray)
}
Playground: https://go.dev/play/p/sNtUZKHC_Rt
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