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

Question

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}

Answer 1

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 Go- Copy all common fields between structs for additional info about this particular situation.

Answer 2

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"`
}

Answer 3

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)