douguanya4248
2016-03-02 03:44
浏览 872

在Golang中执行JSON Unmarshal时如何设置默认值到映射值?

I have a struct like this:

package main

import (
    "encoding/json"
    "fmt"
)

type request struct {
    Version    string               `json:"version"`
    Operations map[string]operation `json:"operations"`
}
type operation struct {
    Type   string `json:"type"`
    Width  int    `json:"width"`
    Height int    `json:"height"`
}

func main() {
    jsonStr := "{\"version\": \"1.0\", \"operations\": {\"0\": {\"type\": \"type1\", \"width\": 100}, \"1\": {\"type\": \"type2\", \"height\": 200}}}"
    req := request{
         Version: "1.0",
    }
    err := json.Unmarshal([]byte(jsonStr), &req)
    if err != nil {
        fmt.Println(err.Error())
    } else {
        fmt.Println(req)
    }
}

I can set Version = "1.0" as its default value, but how can I set default value to Width and Height?

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1条回答 默认 最新

  • douci4026 2016-03-02 04:08
    已采纳

    Write an unmarshal function to set the default values:

    func (o *operation) UnmarshalJSON(b []byte) error {
        type xoperation operation
        xo := &xoperation{Width: 500, Height: 500}
        if err := json.Unmarshal(b, xo); err != nil {
            return err
        }
        *o = operation(*xo)
        return nil
    }
    

    I created a playground example with modifications to the JSON to make it runnable.

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