I have an API response like this:
{
"Pass ✔": true
}
In Go I use this code:
type Status struct {
Pass bool `json:"Pass ✔"`
}
// ...
var s Status
json.Unmarshal(body, &s)
fmt.Println(s.Pass) // false, where it should be true
How can I correctly unmarshal this JSON document?
As others mentioned, it's not currently possible to do that. As a workaround, you could do something like this:
package main
import (
"encoding/json"
"fmt"
)
type status map[string]bool
func (s status) pass() bool {
return s["Pass ✔"]
}
func main() {
data := []byte(`{"Pass ✔": true}`)
var stat status
json.Unmarshal(data, &stat)
pass := stat.pass()
fmt.Println(pass) // true
}
Related
This question already has answers here:
Adding Arbitrary fields to json output of an unknown struct
(2 answers)
Closed 1 year ago.
Here's the response interface :
type Response interface{}
It's satisfied by a struct like this :
type CheckResponse struct {
Status string `json:"status"`
}
I am getting out []Response as an output which is to be consumed elsewhere.
I want to add a Version string to this JSON, before it's being sent. I've tried using anonymous structs ( but in vain ) :
for _, d := range out {
outd := struct {
Resp Response `json:",inline"`
Version string `json:",inline"`
}{
Resp: d,
Version: "1.1",
}
data, _ := json.Marshal(outd)
log.Infof("response : %s", data)
}
The output I am getting is :
response : {"Resp":{"status":"UP"},"Version":"1.1"}
What I want is
{"status":"UP","Version":"1.1"}
i.e. one single flat JSON.
Assert your d to CheckResponse type and then define dynamic struct like this
outd := struct {
Resp string `json:"status,inline"`
Version string `json:",inline"`
}
This is the full code for this.
package main
import (
"encoding/json"
"fmt"
)
type Response interface {}
type CheckResponse struct {
Status string `json:"status"`
}
func main() {
out := []Response{
CheckResponse{Status: "UP"},
}
for _, d := range out {
res, ok := d.(CheckResponse)
if !ok {
continue
}
outd := struct {
Resp string `json:"status,inline"`
Version string `json:",inline"`
}{
Resp: res.Status,
Version: "1.1",
}
data, _ := json.Marshal(outd)
fmt.Printf("response : %s", data)
}
}
You can run here
inline tag is not supported by encoding/json and embedding interfaces will also not produce the result you want. You'll have to declare a type for the out value and have that type implement the json.Marshaler interface, you can then customize how its fields are marshaled, for example you could marshal the two fields Resp and Version separately and then "merge the result" into a single json object.
type VersionedResponse struct {
Resp Response
Version string
}
func (r VersionedResponse) MarshalJSON() ([]byte, error) {
out1, err := json.Marshal(r.Resp)
if err != nil {
return nil, err
}
out2, err := json.Marshal(struct{ Version string }{r.Version})
if err != nil {
return nil, err
}
// NOTE: if Resp can hold something that after marshaling
// produces something other than a json object, you'll have
// to be more careful about how you gonna merge the two outputs.
//
// For example if Resp is nil then out1 will be []byte(`null`)
// If Resp is a slice then out1 will be []byte(`[ ... ]`)
out1[len(out1)-1] = ',' // replace '}' with ','
out2 = out2[1:] // remove leading '{'
return append(out1, out2...), nil
}
https://play.golang.org/p/66jIYXGUtWJ
One way that will work for sure is simply use a map[string]interface{}, iterate over fields in Response via reflect or use a library like structs, update your map with response fields, append your version field to map, and then marshal.
Here is an example
package main
import (
"encoding/json"
"fmt"
"github.com/fatih/structs"
)
type Response interface{}
type CheckResponse struct {
Status string `json:"status"`
}
func main() {
resp := CheckResponse{Status: "success"}
m := structs.Map(resp)
m["Version"] = "0.1"
out, _ := json.Marshal(m)
fmt.Println(string(out))
}
I have below program. I need to convert JSON data into object type cache which contains a single field of map[string]string type. There is something that I am doing wrong w.r.t. initialising map and unmarshalling JSON but unable to identify the syntax issue.
Note: I have marshalled data just for convenience sake to have sample JSON data.
package main
import (
"fmt"
"encoding/json"
"strconv"
)
const data = `{"Mode":{"ID-1":"ON","ID-2":"OFF","ID-3":"ON"}}`
type Cache struct {
Mode map[string]string `json:"Mode"`
}
func main() {
jsonData, _ := json.Marshal(data)
fmt.Println(strconv.Unquote(string(jsonData)))
var c Cache
c.Mode = make(map[string]string) //I want to initialise map so that I can store data in next step, but this is wrong I know
c.Mode["ID-4"] = "ON" //Want to store data like this
json.Unmarshal(jsonData, &c)
fmt.Println(c) //I am getting output as nil map i.e. {map[]}
for k, v := range c.Mode {
fmt.Println(k, v) //I am getting NO output i.e. blank
}
}
Here is your your code fixed https://play.golang.org/p/5ftaiz_Q5wl (attaching blow the copy)
package main
import (
"encoding/json"
"fmt"
"log"
)
const data = `{"Mode":{"ID-1":"ON","ID-2":"OFF","ID-3":"ON"}}`
type Cache struct {
Mode map[string]string `json:"Mode"`
}
func main() {
c := Cache{}
err := json.Unmarshal([]byte(data), &c)
if err != nil {
log.Println(err)
}
c.Mode["ID-4"] = "ON" //Want to store data like this
fmt.Println(c)
for k, v := range c.Mode {
fmt.Println(k, v)
}
}
Here is the output:
{map[ID-1:ON ID-2:OFF ID-3:ON ID-4:ON]}
ID-2 OFF
ID-3 ON
ID-4 ON
ID-1 ON
I am a newbie at GO Programming. Here is scenario :-
There exists a JSON file that looks like this :-
{
"template": "linuxbase1",
"checkname": ["check_disk"],
"checkmethod": ["check_disk"]
}
I am Unmarshalling this data into a structure :-
package func1
import (
"io/ioutil"
"os"
"encoding/json"
"fmt"
)
type pluginfunc func() string
type Plugindata struct {
Template string `json:"template"`
Checkname []string `json:"checkname"`
Checkmethod []pluginfunc `json:"checkmethod"`
}
var (
Templatepath = "json_sample1.json"
Templateitems Plugindata
)
func Gettemplatedata() {
tdata, err := ioutil.ReadFile(Templatepath)
if err != nil {
fmt.Printf("Unable to read file %s. Error - %v\n",Templatepath, err.Error())
os.Exit(3)
}
json.Unmarshal(tdata, &Templateitems)
}
The "check_disk" function is here :-
package func1
func check_disk() string {
return "Called check_disk"
}
This is the program with main() :-
package main
import (
"fmt"
"checksexpt/func1"
)
func main() {
func1.Gettemplatedata()
fmt.Printf("Templateitems in Main() => %v\n",func1.Templateitems)
for index,funcname := range func1.Templateitems.Checkmethod {
fmt.Printf("%d = %s\n",index,funcname())
}
}
As expected, when I run main(); I see the error :-
Templateitems in Main() => {linuxbase1 [check_cpu check_disk] [<nil> <nil>]}
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x40115e]
goroutine 1 [running]:
panic(0x50e980, 0xc82000a100)
/opt/go/src/runtime/panic.go:481 +0x3e6
So, I am trying to grab a string from the JSON file and treat it as a function call. That obviously fails ! But, the primary constraint here is that the function names have to be picked from the JSON file. How can I do this ? I know that I can create a static map as follows :-
type checkfunc func() string
var (
Templateitems = map[string]map[string]checkfunc {
"linuxbase1": {
"check_disk": check_disk,
},
}
)
So, A call like - Templateitems["linuxbase1"]["check_disk"]() would work just fine. But, I dont want to create any such static map as the elements in that map needs to keep growing. Any ideas on this?
There is no direct way to parse a function directly from a JSON value. Also, you cannot use string values to refer to variables. So a string check_cpu would not be able to refer to the function with the same name directly.
What you can do instead is parse the json string as is and have a global map for functions. That way, you can call your functions like so:
var funcMap = map[string]pluginfunc{
"check_disk": check_disk,
"check_cpu": check_cpu
}
In your main loop:
for index, funcname := range func1.Templateitems.Checkmethod {
fmt.Printf("%d = %s\n", index, funcMap[funcname]())
}
If however, you really need to put the value in your structure, you can try implementing UnmarshalJSON from the json.Unmarshaler interface. A simple example would be:
type pf map[string]pluginfunc
type Plugindata struct {
Template string `json:"template"`
Checkname []string `json:"checkname"`
Checkmethod pf `json:"checkmethod"`
}
func (p *pf) UnmarshalJSON(data []byte) error {
d := []string{}
if err := json.Unmarshal(data, &d); err != nil {
return err
}
*p = make(pf)
for _, s := range d {
(*p)[s] = funcMap[s]
}
return nil
}
var funcMap = pf{
"check_disk": check_disk,
"check_cpu": check_cpu
}
func main() {
json.Unmarshal(tdata, &Templateitems)
for k, f := range Templateitems.Checkmethod {
fmt.Printf("%s -- %s\n", k, f())
}
}
Working code
Note that this way is not as readable or simple as the first method and it still relies on a function map.
You can read more about json.Unmarshaler here.
I want to convert a struct to map in Golang. It would also be nice if I could use the JSON tags as keys in the created map (otherwise defaulting to field name).
Edit Dec 14, 2020
Since structs repo was archived, you can use mapstructure instead.
Edit TL;DR version, Jun 15, 2015
If you want the fast solution for converting a structure to map, see the accepted answer, upvote it and use that package.
Happy coding! :)
Original Post
So far I have this function, I am using the reflect package but I don't understand well how to use the package, please bear with me.
func ConvertToMap(model interface{}) bson.M {
ret := bson.M{}
modelReflect := reflect.ValueOf(model)
if modelReflect.Kind() == reflect.Ptr {
modelReflect = modelReflect.Elem()
}
modelRefType := modelReflect.Type()
fieldsCount := modelReflect.NumField()
var fieldData interface{}
for i := 0; i < fieldsCount; i++ {
field := modelReflect.Field(i)
switch field.Kind() {
case reflect.Struct:
fallthrough
case reflect.Ptr:
fieldData = ConvertToMap(field.Interface())
default:
fieldData = field.Interface()
}
ret[modelRefType.Field(i).Name] = fieldData
}
return ret
}
Also I looked at JSON package source code, because it should contain my needed implementation (or parts of it) but don't understand too much.
I also had need for something like this. I was using an internal package which was converting a struct to a map. I decided to open source it with other struct based high level functions. Have a look:
https://github.com/fatih/structs
It has support for:
Convert struct to a map
Extract the fields of a struct to a []string
Extract the values of a struct to a []values
Check if a struct is initialized or not
Check if a passed interface is a struct or a pointer to struct
You can see some examples here: http://godoc.org/github.com/fatih/structs#pkg-examples
For example converting a struct to a map is a simple:
type Server struct {
Name string
ID int32
Enabled bool
}
s := &Server{
Name: "gopher",
ID: 123456,
Enabled: true,
}
// => {"Name":"gopher", "ID":123456, "Enabled":true}
m := structs.Map(s)
The structs package has support for anonymous (embedded) fields and nested structs. The package provides to filter certain fields via field tags.
From struct to map[string]interface{}
package main
import (
"fmt"
"encoding/json"
)
type MyData struct {
One int
Two string
Three int
}
func main() {
in := &MyData{One: 1, Two: "second"}
var inInterface map[string]interface{}
inrec, _ := json.Marshal(in)
json.Unmarshal(inrec, &inInterface)
// iterate through inrecs
for field, val := range inInterface {
fmt.Println("KV Pair: ", field, val)
}
}
go playground here
Here is a function I've written in the past to convert a struct to a map, using tags as keys
// ToMap converts a struct to a map using the struct's tags.
//
// ToMap uses tags on struct fields to decide which fields to add to the
// returned map.
func ToMap(in interface{}, tag string) (map[string]interface{}, error){
out := make(map[string]interface{})
v := reflect.ValueOf(in)
if v.Kind() == reflect.Ptr {
v = v.Elem()
}
// we only accept structs
if v.Kind() != reflect.Struct {
return nil, fmt.Errorf("ToMap only accepts structs; got %T", v)
}
typ := v.Type()
for i := 0; i < v.NumField(); i++ {
// gets us a StructField
fi := typ.Field(i)
if tagv := fi.Tag.Get(tag); tagv != "" {
// set key of map to value in struct field
out[tagv] = v.Field(i).Interface()
}
}
return out, nil
}
Runnable example here.
Note, if you have multiple fields with the same tag value, then you will obviously not be able to store them all within a map. It might be prudent to return an error if that happens.
I like the importable package for the accepted answer, but it does not translate my json aliases. Most of my projects have a helper function/class that I import.
Here is a function that solves my specific problem.
// Converts a struct to a map while maintaining the json alias as keys
func StructToMap(obj interface{}) (newMap map[string]interface{}, err error) {
data, err := json.Marshal(obj) // Convert to a json string
if err != nil {
return
}
err = json.Unmarshal(data, &newMap) // Convert to a map
return
}
And in the main, this is how it would be called...
package main
import (
"fmt"
"encoding/json"
"github.com/fatih/structs"
)
type MyStructObject struct {
Email string `json:"email_address"`
}
func main() {
obj := &MyStructObject{Email: "test#test.com"}
// My solution
fmt.Println(StructToMap(obj)) // prints {"email_address": "test#test.com"}
// The currently accepted solution
fmt.Println(structs.Map(obj)) // prints {"Email": "test#test.com"}
}
package main
import (
"fmt"
"reflect"
)
type bill struct {
N1 int
N2 string
n3 string
}
func main() {
a := bill{4, "dhfthf", "fdgdf"}
v := reflect.ValueOf(a)
values := make(map[string]interface{}, v.NumField())
for i := 0; i < v.NumField(); i++ {
if v.Field(i).CanInterface() {
values[v.Type().Field(i).Name] = v.Field(i).Interface()
} else {
fmt.Printf("sorry you have a unexported field (lower case) value you are trying to sneak past. I will not allow it: %v\n", v.Type().Field(i).Name)
}
}
fmt.Println(values)
passObject(&values)
}
func passObject(v1 *map[string]interface{}) {
fmt.Println("yoyo")
}
I'm a bit late but I needed this kind of feature so I wrote this. Can resolve nested structs. By default, uses field names but can also use custom tags. A side effect is that if you set the tagTitle const to json, you could use the json tags you already have.
package main
import (
"fmt"
"reflect"
)
func StructToMap(val interface{}) map[string]interface{} {
//The name of the tag you will use for fields of struct
const tagTitle = "kelvin"
var data map[string]interface{} = make(map[string]interface{})
varType := reflect.TypeOf(val)
if varType.Kind() != reflect.Struct {
// Provided value is not an interface, do what you will with that here
fmt.Println("Not a struct")
return nil
}
value := reflect.ValueOf(val)
for i := 0; i < varType.NumField(); i++ {
if !value.Field(i).CanInterface() {
//Skip unexported fields
continue
}
tag, ok := varType.Field(i).Tag.Lookup(tagTitle)
var fieldName string
if ok && len(tag) > 0 {
fieldName = tag
} else {
fieldName = varType.Field(i).Name
}
if varType.Field(i).Type.Kind() != reflect.Struct {
data[fieldName] = value.Field(i).Interface()
} else {
data[fieldName] = StructToMap(value.Field(i).Interface())
}
}
return data
}
map := Structpb.AsMap()
// map is the map[string]interface{}
I am trying to convert a Go struct to JSON using the json package but all I get is {}. I am certain it is something totally obvious but I don't see it.
package main
import (
"fmt"
"encoding/json"
)
type User struct {
name string
}
func main() {
user := &User{name:"Frank"}
b, err := json.Marshal(user)
if err != nil {
fmt.Printf("Error: %s", err)
return;
}
fmt.Println(string(b))
}
Then when I try to run it I get this:
$ 6g test.go && 6l -o test test.6 && ./test
{}
You need to export the User.name field so that the json package can see it. Rename the name field to Name.
package main
import (
"fmt"
"encoding/json"
)
type User struct {
Name string
}
func main() {
user := &User{Name: "Frank"}
b, err := json.Marshal(user)
if err != nil {
fmt.Println(err)
return
}
fmt.Println(string(b))
}
Output:
{"Name":"Frank"}
Related issue:
I was having trouble converting struct to JSON, sending it as response from Golang, then, later catch the same in JavaScript via Ajax.
Wasted a lot of time, so posting solution here.
In Go:
// web server
type Foo struct {
Number int `json:"number"`
Title string `json:"title"`
}
foo_marshalled, err := json.Marshal(Foo{Number: 1, Title: "test"})
fmt.Fprint(w, string(foo_marshalled)) // write response to ResponseWriter (w)
In JavaScript:
// web call & receive in "data", thru Ajax/ other
var Foo = JSON.parse(data);
console.log("number: " + Foo.number);
console.log("title: " + Foo.title);
This is an interesting question, it is very easy using the new go versions. You should do this:
package main
import (
"fmt"
"encoding/json"
)
type User struct {
Name string `json:"name"`
}
func main() {
user := &User{name:"Frank"}
b, err := json.Marshal(user)
if err != nil {
fmt.Printf("Error: %s", err)
return;
}
fmt.Println(string(b))
}
Change this name to Name.
You can define your own custom MarshalJSON and UnmarshalJSON methods and intentionally control what should be included, ex:
package main
import (
"fmt"
"encoding/json"
)
type User struct {
name string
}
func (u *User) MarshalJSON() ([]byte, error) {
return json.Marshal(&struct {
Name string `json:"name"`
}{
Name: "customized" + u.name,
})
}
func main() {
user := &User{name: "Frank"}
b, err := json.Marshal(user)
if err != nil {
fmt.Println(err)
return
}
fmt.Println(string(b))
}
Struct values encode as JSON objects. Each exported struct field becomes
a member of the object unless:
the field's tag is "-", or
the field is empty and its tag specifies the "omitempty" option.
The empty values are false, 0, any nil pointer or interface value, and any array, slice, map, or string of length zero. The object's default key string is the struct field name but can be specified in the struct field's tag value. The "json" key in the struct field's tag value is the key name, followed by an optional comma and options.