I have to unmarshal a series of Json objects, but one of the objects contain a json array which is not really structured in a good way.
"labels": [
{
"key": "owner",
"value": "harry"
},
{
"key": "group",
"value": "student"
}
]
I am unmarshalling it using this struct -
type StudentDetails struct {
Id string `json:"id"`
Name string `json:"name"`
Labels []Label `json:"labels,omitempty"`
}
type Label struct {
Key string `json:"key"`
Value string `json:"value"`
}
And I have to access it using x.Labels[0].key == "owner" inside a for loop which is very annoying.
I want to be able to do x.Labels.Owner == "harry" instead. How do I go about achieving this? The rest of JSON is unmarshalled fine using the default unmarshal function, so I don't think writing custom function will be good option.
With the constraints you have here, this is about as close as you will get (run in playground):
package main
import (
"encoding/json"
"fmt"
)
func main() {
j := `
{
"id": "42",
"name": "Marvin",
"labels": [
{
"key": "owner",
"value": "harry"
},
{
"key": "group",
"value": "student"
}
]
}`
d := StudentDetails{}
err := json.Unmarshal([]byte(j), &d)
if err != nil {
panic(err)
}
fmt.Println(d.Labels["owner"])
fmt.Println(d.Labels["group"])
}
type StudentDetails struct {
Id string `json:"id"`
Name string `json:"name"`
Labels Labels `json:"labels"`
}
type Labels map[string]string
func (l *Labels) UnmarshalJSON(b []byte) error {
a := []map[string]string{}
err := json.Unmarshal(b, &a)
if err != nil {
return err
}
t := map[string]string{}
for _, m := range a {
t[m["key"]] = m["value"]
}
*l = t
return nil
}
How about to define custom []Label type and add function on it.
For instance
type Labels []Label
func (l Labels) Owner() string {
if len(l) > 1 {
return l[0].Value
}
return ""
}
Related
I have a json file sample.json containing a json array as follows:
[
{
"time": "2021-01-04T00:11:32.362Z",
"extra_data": {
"id": "123"
},
"info": "event123"
},
{
"time": "2021-01-05T00:11:32.362Z",
"extra_data": {
"id": "456"
},
"info": "event456"
},
{
"time": "2021-01-06T00:11:32.362Z",
"extra_data": {
"id": "789"
},
"info": "event789"
}
]
I am trying to unmarshal this json array so that for each json object (i.e. event), I can access the id and info values. This is what I have so far:
func main() {
file, err := ioutil.ReadFile("/Users/janedoe/Downloads/sample.json")
var events Event
json.Unmarshal([]byte(file), &events)
fmt.Println(reflect.TypeOf(events))
// Reading each value by its key for each event
fmt.Println("Event123_Time :", events.Timestamp,
"\nEvent123_ExtraData_Id :", events.ExtraData.Id,
"\nEvent123_Info :", events.Info)
}
type Event struct {
Time string `json:"time"`
ExtraData ExtraData `json:"extra_data"`
Info string `json:"info"`
}
type ExtraData struct {
Id string `json:"id"`
}
The output that I am getting is:
main.Event
Event123_Time :
Event123_ExtraData_Id :
Event123_Info :
I am not getting any values, implying that the marshalling is not happening as expected. How can I fix this?
Since your json is an array, I think you want:
var events []Event
not
var events Event
Here's a version with that change:
func main() {
file, err := ioutil.ReadFile("/Users/janedoe/Downloads/sample.json")
if err != nil {
panic(err)
}
var events []Event
if err := json.Unmarshal([]byte(file), &events); err != nil {
panic(err)
}
fmt.Println(reflect.TypeOf(events))
for i, event := range events {
// Reading each value by its key for each event
fmt.Println(i, "Event123_Time :", event.Time,
"\nEvent123_ExtraData_Id :", event.ExtraData.Id,
"\nEvent123_Info :", event.Info)
}
}
type Event struct {
Time string `json:"time"`
ExtraData ExtraData `json:"extra_data"`
Info string `json:"info"`
}
type ExtraData struct {
Id string `json:"id"`
}
I have a json stream as follows ...
[
{
"page": 1,
"pages": 7,
"per_page": "2000",
"total": 13200
},
[
{
"indicator": {
"id": "SP.POP.TOTL",
"value": "Population, total"
},
"country": {
"id": "1A",
"value": "Arab World"
},
"value": null,
"decimal": "0",
"date": "2019"
},
{
"indicator": {
"id": "SP.POP.TOTL",
"value": "Population, total"
},
"country": {
"id": "1A",
"value": "Arab World"
},
"value": "419790588",
"decimal": "0",
"date": "2018"
},
...
]
]
And I'm trying to decode it ... so I have the following struct ... but I keep getting
"cannot unmarshal array into Go value of type struct { P struct ... "
type Message []struct {
P struct {
Page int
}
V []struct {
Indicator struct {
Id string
Value string
}
Country struct {
Value string
}
Value string
Decimal string
Date string
}
}
My struct looks to match the json ... but obviously not! Any ideas?
Since your JSON array have two different types first unmarshal them into a slice of json.RawMessage which is []byte as underlying type so that we can unmarshal again JSON array data.
So unmarshal data for P and V struct type using index directly (predict) or detect if object(starting with '{') then unmarshal into P and array(starting with '[') then unmarshal into V. Now prepare your Message using those data.
type Message struct {
PageData P
ValData []V
}
type P struct {
Page int
}
type V struct {
Indicator struct {
Id string
Value string
}
Country struct {
Value string
}
Value string
Decimal string
Date string
}
func main() {
var rawdata []json.RawMessage
json.Unmarshal([]byte(jsonData), &rawdata)
var pageData P
json.Unmarshal(rawdata[0], &pageData)
var valData []V
json.Unmarshal(rawdata[1], &valData)
res := Message{pageData, valData}
fmt.Println(res)
}
var jsonData = `[...]` //your json data
Full code in Go Playground
As poWar said, the JSON you actually have is a list of objects whose types do not conform to each other. You must therefore unmarshal into something capable of holding different object types, such as interface{} or—since there is an outer array—[]interface{}.
You can also, if you like, decode into a []json.RawMessage. The underlying json.RawMessage itself has underlying type []byte so that it's basically the undecoded "inner" JSON. In at least some cases this is going to be more work than just decoding directly to []interface{} and checking each resulting interface, but you can, if you wish, decode to struct once you have the JSON separated out. For instance:
func main() {
var x []json.RawMessage
err := json.Unmarshal(input, &x)
if err != nil {
fmt.Printf("err = %v\n", err)
return
}
if len(x) != 2 {
fmt.Println("unexpected input")
return
}
var page struct {
Page int
}
err = json.Unmarshal(x[0], &page)
if err != nil {
fmt.Printf("unable to unmarshal page part: %v\n", err)
return
}
fmt.Printf("page = %d\n", page.Page)
// ...
}
Here on the Go Playground is a more complete example. See also Eklavya's answer.
Looking at your struct, your corresponding JSON should look something like this.
[
{
"P": {"page": 1},
"V": [
{
"Indicator": {"Id": ...},
"Country": {"Value":""},
"Value": "",
...
}
]
},
...
]
The JSON structure you are trying to Unmarshal looks like a list of objects where each object is not of the same type. You can start unmarshalling them into interfaces and defining each interface based on the object being unmarhsalled.
package main
import (
"encoding/json"
"log"
)
type Message []interface{}
func main() {
data := `[{"page":1,"pages":7,"per_page":"2000","total":13200},[{"indicator":{"id":"SP.POP.TOTL","value":"Population, total"},"country":{"id":"1A","value":"Arab World"},"value":null,"decimal":"0","date":"2019"},{"indicator":{"id":"SP.POP.TOTL","value":"Population, total"},"country":{"id":"1A","value":"Arab World"},"value":"419790588","decimal":"0","date":"2018"}]]`
var m Message
if err := json.Unmarshal([]byte(data), &m); err != nil {
log.Fatalf("could not unmarshal")
}
log.Printf("message: %v", m)
}
Output:
message: [map[page:1 pages:7 per_page:2000 total:13200] [map[country:map[id:1A value:Arab World] date:2019 decimal:0 indicator:map[id:SP.POP.TOTL value:Population, total] value:<nil>] map[country:map[id:1A value:Arab World] date:2018 decimal:0 indicator:map[id:SP.POP.TOTL value:Population, total] value:419790588]]]
[Edit]: Ideally you should change your JSON to be structured better for unmarshalling. If you do not have control on it, then your corresponding Go structure is just embedded maps of string to interfaces, which you will have to manually type cast and access.
I have json as following
"data": [
{
"id": "recent_search",
"items": [],
"name": ""
},
{
"id": "popular_search",
"items": [],
"name": ""
},
{
"id": "digital",
"items": [],
"name": "DIGITAL"
}
]
and the structs are as follows:
type universeTypeData struct {
Recent universeSearchInfo
Popular universeSearchInfo
Digital universeSearchInfo
}
type universeSearchInfo struct {
ID string `json:"id"`
Name string `json:"name"`
Items []universeSearchItem `json:"items"`
}
I want to unmarshal my json as "id" with value "recent_search" map to Recent, "id" with value "popular_search" map to Popular. Is there any way of doing this in golang?
My approach of doing it is
for _, v := range result.Data {
if v.ID == "in_category" {
finalResult.Universe.InCategory.ID = v.ID
finalResult.Universe.InCategory.Name = v.Name
for _, abc := range v.Items {
finalResult.Universe.InCategory.Items = append(finalResult.Universe.InCategory.Items, abc)
}
}
if v.ID == "recent_search" {
finalResult.Universe.Recent.ID = v.ID
finalResult.Universe.Recent.Name = v.Name
for _, abc := range v.Items {
finalResult.Universe.Recent.Items = append(finalResult.Universe.Recent.Items, abc)
}
}
if v.ID == "popular_search" {
finalResult.Universe.Popular.ID = v.ID
finalResult.Universe.Popular.Name = v.Name
for _, abc := range v.Items {
finalResult.Universe.Popular.Items = append(finalResult.Universe.Popular.Items, abc)
}
}
Is there any better way of doing it?
You want to unmurshal JSON array into Go struct which is not natural mapping. Any way, you most likely should be first unmurshal in slice and then parse this slice. Some workaround is to use json.Decoder
dec := json.NewDecoder(JSONdataReader)
var res universeTypeData
// read open bracket
dec.Token()
// while the array contains values
for dec.More() {
var m universeSearchInfo
// decode an array value
dec.Decode(&m)
switch m.ID {
case "recent_search":
res.Recent = m
case "popular_search":
res.Popular = m
case "digital":
res.Digital = m
}
}
// read closing bracket
dec.Token()
which allow you to decode on the fly, in one pass, without consuming intermediate slice representation. Working example
Implement Unmarshaler interface:
Unmarshaler is the interface implemented by types that can unmarshal a
JSON description of themselves. The input can be assumed to be a valid
encoding of a JSON value. UnmarshalJSON must copy the JSON data if it
wishes to retain the data after returning.
json unmarshaler interface assign the value from json to struct after parsing the result and applying conditions to fetch the value.
package main
import (
"encoding/json"
"fmt"
)
type Details struct {
Data []universeSearchInfo `json:"data"`
}
type universeTypeData struct {
Recent universeSearchInfo
Popular universeSearchInfo
Digital universeSearchInfo
}
type universeSearchInfo struct {
ID string `json:"id"`
Name string `json:"name"`
Items []string `json:"items"`
}
func main() {
var result universeTypeData
jsonBytes := []byte(`{"data": [
{
"id": "recent_search",
"items": [],
"name": ""
},
{
"id": "popular_search",
"items": [],
"name": ""
},
{
"id": "digital",
"items": [],
"name": "DIGITAL"
}
]}`)
if err := json.Unmarshal(jsonBytes, &result); err != nil {
fmt.Println(err)
}
fmt.Println(result)
}
func (universeData *universeTypeData) UnmarshalJSON(data []byte) error {
var result Details
if err := json.Unmarshal(data, &result); err != nil {
return err
}
for _,value := range result.Data{
switch value.ID {
case "recent_search":
universeData.Recent = value
}
}
return nil
}
Working code on Go Playground
I am trying to unmarshal JSON of the following format:
{
"fixedString": {
"uselessStuff": {},
"alsoUseless": {},
"dynamicField": [
{ "name": "jack" }
],
"dynamicToo": [
{ "name": "jill" }
]
}
}
I would like to drop the fields "uselessStuff" and "alsoUseless", and get everything else. The other keys are user-defined and can take any value.
I can remove the fields I don't want using a custom UnmarshalJSON (based on this answer), but I have a feeling that this is unnecessarily complicated:
package main
import (
"encoding/json"
"fmt"
)
type Response struct {
Things map[string]interface{} `json:"fixedString"`
}
type _R Response
func (f *Response) UnmarshalJSON(bs []byte) (err error) {
foo := _R{}
if err = json.Unmarshal(bs, &foo); err == nil {
*f = Response(foo)
}
delete(f.Things, "uselessStuff")
delete(f.Things, "alsoUseless")
return err
}
func main() {
j := []byte(`{ "fixedString": { "uselessStuff": {}, "alsoUseless": {}, "dynamicField": [ { "name": "jack" } ], "dynamicToo": [ { "name": "jill" } ] } }`)
var r Response
err := json.Unmarshal(j, &r)
if err != nil {
panic(err.Error())
}
for x, y := range r.Things {
fmt.Println(x, y)
}
}
Is there a way to ignore those two keys using annotations, rather than deleting them in a custom UnmarshalJSON function (and having to add the extra type alias _R to avoid a stack overflow)?
You could remove your "uselessStuff" and "alsoUseless" from the map and use them as unexported (lowercase) fields in your struct. Most likely not interface{}
json package ignores unexported fields
type Response struct {
Things map[string]interface{} `json:"fixedString"`
uselessStuff interface{}
alsoUseless interface{}
}
I am having difficulty understanding how to correctly unmarshal some JSON data that goes in to an array of type inteface and then use it. I tried to make this example code as simple as possible to illustrate the problem I am having. The code can be found in the playground here: https://play.golang.org/p/U85J_lBJ7Zr
The output looks like:
[map[ObjectType:chair ID:1234 Brand:Blue Inc.] map[ID:5678
Location:Kitchen ObjectType:table]] { } false { } false
Code
package main
import (
"fmt"
"encoding/json"
)
type Chair struct {
ObjectType string
ID string
Brand string
}
type Table struct {
ObjectType string
ID string
Location string
}
type House struct {
Name string
Objects []interface{}
}
func main() {
var h House
data := returnJSONBlob()
err := json.Unmarshal(data, &h)
if err != nil {
fmt.Println(err)
}
fmt.Println(h.Objects)
s1, ok := h.Objects[0].(Table)
fmt.Println(s1, ok)
s2, ok := h.Objects[0].(Chair)
fmt.Println(s2, ok)
}
func returnJSONBlob() []byte {
s := []byte(`
{
"Name": "house1",
"Objects": [
{
"ObjectType": "chair",
"ID": "1234",
"Brand": "Blue Inc."
},
{
"ObjectType": "table",
"ID": "5678",
"Location": "Kitchen"
}
]
}
`)
return s
}
I'm not sure if this is practical, since this is a simplified version of your scenario. However, one way to do this is combine the two object types to a new one, Object, and then unmarshal them directly to Object instead of using interface{}:
package main
import (
"encoding/json"
"fmt"
)
type Object struct {
ObjectType string
ID string
Brand string
Location string
}
type House struct {
Name string
Objects []Object
}
func returnJSONBlob() []byte {
s := []byte(`
{
"Name": "house1",
"Objects": [
{
"ObjectType": "chair",
"ID": "1234",
"Brand": "Blue Inc."
},
{
"ObjectType": "table",
"ID": "5678",
"Location": "Kitchen"
}
]
}
`)
return s
}
func main() {
var h House
data := returnJSONBlob()
err := json.Unmarshal(data, &h)
if err != nil {
fmt.Println(err)
}
fmt.Println(h.Objects[0].Brand)
fmt.Println(h.Objects[1].Location)
}
Prints:
Blue Inc.
Kitchen
Example here: https://play.golang.org/p/91F4UrQlSjJ