Write Struct to Json File using Struct Fields (not json keys)

How can I read a json file into a struct, and then Marshal it back out to a json string with the Struct fields as keys (rather than the original json keys)?

(see Desired Output to Json File below...)

Code:

package main

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

type Rankings struct {
	Keyword  string `json:"keyword"`
	GetCount uint32 `json:"get_count"`
	Engine   string `json:"engine"`
	Locale   string `json:"locale"`
	Mobile   bool   `json:"mobile"`
}

func main() {
	var jsonBlob = []byte(`
		{"keyword":"hipaa compliance form", "get_count":157, "engine":"google", "locale":"en-us", "mobile":false}
	`)
	rankings := Rankings{}
	err := json.Unmarshal(jsonBlob, &rankings)
	if err != nil {
		// nozzle.printError("opening config file", err.Error())
	}

	rankingsJson, _ := json.Marshal(rankings)
	err = ioutil.WriteFile("output.json", rankingsJson, 0644)
	fmt.Printf("%+v", rankings)
}

Output on screen:

{Keyword:hipaa compliance form GetCount:157 Engine:google Locale:en-us Mobile:false}

Output to Json File:

{"keyword":"hipaa compliance form","get_count":157,"engine":"google","locale":"en-us","mobile":false}

Desired Output to Json File:

{"Keyword":"hipaa compliance form","GetCount":157,"Engine":"google","Locale":"en-us","Mobile":false}

If I understand your question correctly, all you want to do is remove the json tags from your struct definition.

So:

package main

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

type Rankings struct {
    Keyword  string 
    GetCount uint32 
    Engine   string 
    Locale   string 
    Mobile   bool   
}

func main() {
    var jsonBlob = []byte(`
        {"keyword":"hipaa compliance form", "get_count":157, "engine":"google", "locale":"en-us", "mobile":false}
    `)
    rankings := Rankings{}
    err := json.Unmarshal(jsonBlob, &rankings)
    if err != nil {
        // nozzle.printError("opening config file", err.Error())
    }

    rankingsJson, _ := json.Marshal(rankings)
    err = ioutil.WriteFile("output.json", rankingsJson, 0644)
    fmt.Printf("%+v", rankings)
}

Results in:

{Keyword:hipaa compliance form GetCount:0 Engine:google Locale:en-us Mobile:false}

And the file output is:

{"Keyword":"hipaa compliance form","GetCount":0,"Engine":"google","Locale":"    en-us","Mobile":false}

Running example at http://play.golang.org/p/dC3s37HxvZ

Note: GetCount shows 0, since it was read in as "get_count". If you want to read in JSON that has "get_count" vs. "GetCount", but output "GetCount" then you'll have to do some additional parsing.

See https://stackoverflow.com/q/11527935/1162491 for additional info about this particular situation.

Try to change the json format in the struct

type Rankings struct {
    Keyword  string `json:"Keyword"`
    GetCount uint32 `json:"Get_count"`
    Engine   string `json:"Engine"`
    Locale   string `json:"Locale"`
    Mobile   bool   `json:"Mobile"`
}

An accourance happened by just using json.Marshal() / json.MarshalIndent().
It overwrites the existing file, which in my case was suboptimal. I just wanted to add content to current file, and keep old content.

This writes data through a buffer, with bytes.Buffer type.

This is what I gathered up so far:

package srf

import (
	"bytes"
	"encoding/json"
	"os"
)

func WriteDataToFileAsJSON(data interface{}, filedir string) (int, error) {
	//write data as buffer to json encoder
	buffer := new(bytes.Buffer)
	encoder := json.NewEncoder(buffer)
	encoder.SetIndent("", "\t")

	err := encoder.Encode(data)
	if err != nil {
		return 0, err
	}
	file, err := os.OpenFile(filedir, os.O_RDWR|os.O_CREATE, 0755)
	if err != nil {
		return 0, err
	}
	n, err := file.Write(buffer.Bytes())
	if err != nil {
		return 0, err
	}
	return n, nil
}

This is the execution of the function, together with the standard json.Marshal() or json.MarshalIndent() which overwrites the file

package main

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

	minerals "./minerals"
	srf "./srf"
)

func main() {

	//array of Test struct
	var SomeType [10]minerals.Test

	//Create 10 units of some random data to write
	for a := 0; a < 10; a++ {
		SomeType[a] = minerals.Test{
			Name:   "Rand",
			Id:     123,
			A:      "desc",
			Num:    999,
			Link:   "somelink",
			People: []string{"John Doe", "Aby Daby"},
		}
	}

	//writes aditional data to existing file, or creates a new file
	n, err := srf.WriteDataToFileAsJSON(SomeType, "test2.json")
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println("srf printed ", n, " bytes to ", "test2.json")
	
	//overrides previous file
	b, _ := json.MarshalIndent(SomeType, "", "\t")
	ioutil.WriteFile("test.json", b, 0644)

}

Why is this useful?
File.Write() returns bytes written to the file! So this is perfect if you want to manage memory or storage.

WriteDataToFileAsJSON() (numberOfBytesWritten, error)