为什么JSON值是空的

Question

Can you see why json values dont get saved:

Update: And if you would like to explain why this is downgraded as "Off topic"?

package main

import (
    "encoding/json"
    "fmt"
    "io/ioutil"
)

type UsedInContext struct {
    UsedIn      string `json:"usedin"`
    ContextName string `json:"contextname"`
}

type ContextData struct {
    usedInContext []UsedInContext `json:"usedincontext"`
}

func saveData() {

    var jsonBlob = []byte(`{
        "usedincontext": 
        [
            {"usedin":"local", "contextname":"desktop"}
        ]
    }`)

    usedInContext := UsedInContext{}
    err := json.Unmarshal(jsonBlob, &usedInContext)
    if err != nil {
    }

    usedInContextJson, _ := json.Marshal(usedInContext)
    err = ioutil.WriteFile("data.json", usedInContextJson, 0644)
    fmt.Printf("%+v", usedInContext)
}

I get the following:

{"usedin":"","contextname":""}

Answer 1

You unmarshal your document to the type UsedInContext, while it matches the schema for ContextData:

type ContextData struct {
    UsedInContext []UsedInContext `json:"usedincontext"` // exported
}

var data ContextData
json.Unmarshal(jsonBlob, &data)
fmt.Printf("%+v", data)