I am trying to Unmarshal the following JSON object which is generated by couchDB and returns for a cURL request in Go, the cURL request code is not mentioned here as it is out of scope of this question and I have assigned it to the variable called mail in the code section.
the JSON data structure:
{
"total_rows": 4,
"offset": 0,
"rows": [{
"id": "36587e5d091a0d49f739c25c0b000c05",
"key": "36587e5d091a0d49f739c25c0b000c05",
"value": {
"rev": "1-92471472a3de492b8657d3103f5f6e0d"
}
}]
}
and here is my code to unmarshel the above JSON object,
package main
import (
"fmt"
"encoding/json"
)
type Couchdb struct {
TotalRows int `json:"total_rows"`
Offset int `json:"offset"`
Rows []struct {
ID string `json:"id"`
Key string `json:"key"`
Value struct {
Rev string `json:"rev"`
} `json:"value"`
} `json:"rows"`
}
func main() {
mail := []byte(`{"total_rows":4,"offset":0,"rows":[{"id":"36587e5d091a0d49f739c25c0b000c05","key":"36587e5d091a0d49f739c25c0b000c05","value":{"rev":"1-92471472a3de492b8657d3103f5f6e0d"}}]}`)
var s Couchdb
err := json.Unmarshal(mail, &s)
if err != nil {
panic(err)
}
//fmt.Printf("%v", s.TotalRows)
fmt.Printf("%v", s.Rows)
}
and the above code is working fine and you can access the working code here with this link in the Go Play Ground.
I need to get the 36587e5d091a0d49f739c25c0b000c05 value which is the id of rows so I am trying to do it like this
fmt.Printf("%v", s.Rows.ID)
and it returns this error
prog.go:33:25: s.Rows.ID undefined (type []struct { ID string "json:\"id\""; Key string "json:\"key\""; Value struct { Rev string "json:\"rev\"" } "json:\"value\"" } has no field or method ID)
but it works for fmt.Printf("%v", s.Rows) and it returns
[{36587e5d091a0d49f739c25c0b000c05 36587e5d091a0d49f739c25c0b000c05 {1-92471472a3de492b8657d3103f5f6e0d}}]
My ultimate goal is to get 36587e5d091a0d49f739c25c0b000c05 and assign it to GO variable but stuck getting that value using GO.
You have to call :
fmt.Println(s.Rows[0].ID)
You define Rows as slice of struct that means you should iterate Rows with for for execution of values.
for _, item := range s.Rows {
fmt.Println(item.ID)
}
Related
This is the Go code that I have:
func main(){
s := string(`{"Id": "ABC123",
"Name": "Hello",
"RelatedItems":[
{"RId":"TEST123","RName":"TEST1","RChildren":"Ch1"},
{"RId":"TEST234","RName":"TEST2","RChildren":"Ch2"}]
}`)
var result map[string]interface{}
json.Unmarshal([]byte(s), &result)
fmt.Println("Id:", result["Id"])
Rlist := result["RelatedItems"].([]map[string]interface{})
for key, pist := range pist {
fmt.Println("Key: ", key)
fmt.Println("RID:", pist["RId"])
}
}
The struct is down below
type Model struct {
Id string `json:"Id"`
Name string `json:"ModelName"`
RelatedItems []RelatedItems `json:"RelatedItems"`
}
type RelatedItems struct {
RId string `json:"PCId"`
RName string `json:"PCName"`
RChildren string `json:"string"`
}
How would I get an output that would let me choose a particular field from the above?
eg:
Output
Id: ABC123
key:0
RID:TEST123
key:1
RID:TEST234
I am seeing this error
panic: interface conversion: interface {} is nil, not []map[string]interface {}
Based on the posted content,
I'm clear that you are facing issues retrieving data from the nested JSON string.
I've taken your piece of code and tried to compile and reproduce the issue.
After observing, I have a few suggestions based on the way the code has been written.
When the datatype present in the s is known to be similar to the type Model, the result could have been declared as type Model.
That results in var result Model instead of map[string]interface{}.
When the data that's gonna be decoded from the interface{} is not known, the usage of switch would come into rescue without crashing the code.
Something similar to:
switch dataType := result["RelatedItems"].(type){
case interface{}:
// Handle interface{}
case []map[string]interface{}:
// Handle []map[string]interface{}
default:
fmt.Println("Unexpected-Datatype", dataType)
// Handle Accordingly
When we try to Unmarshal, we make sure to look into the json tags that are provided for the fields of a structure. If the data encoded is not having the tags we provided, the data will not be decoded accordingly.
Hence, the result of decoding the data from s into result would result in {ABC123 [{ } { }]} as the tags of the fields Name, RId, RName, RChildren are given as ModelName, PCId, PCName, string respectively.
By the above suggestions and refining the tags given, the piece of code would be as following which would definitely retrieve data from nested JSON structures.
s := string(`{"Id": "ABC123",
"Name": "Hello",
"RelatedItems":[
{"RId":"TEST123","RName":"TEST1","RChildren":"Ch1"},
{"RId":"TEST234","RName":"TEST2","RChildren":"Ch2"}]
}`)
var result Model
json.Unmarshal([]byte(s), &result)
fmt.Println(result)
type Model struct {
Id string `json:"Id"`
Name string `json:"Name"`
RelatedItems []RelatedItems `json:"RelatedItems"`
}
type RelatedItems struct {
RId string `json:"RId"`
RName string `json:"RName"`
RChildren string `json:"RChildren"`
}
This results in the output: {ABC123 Hello [{TEST123 TEST1 Ch1} {TEST234 TEST2 Ch2}]}
Why would you unmarshal to a map anyway and go through type checks?
type Model struct {
Id string `json:"Id"`
Name string `json:"ModelName"`
RelatedItems []RelatedItems `json:"RelatedItems"`
}
type RelatedItems struct {
RId string `json:"PCId"`
RName string `json:"PCName"`
RChildren string `json:"string"`
}
s := `{"Id": "ABC123",
"Name": "Hello",
"RelatedItems":[
{"RId":"TEST123","RName":"TEST1","RChildren":"Ch1"},
{"RId":"TEST234","RName":"TEST2","RChildren":"Ch2"}]
}`
var result Model
if err := json.Unmarshal([]byte(s), &result); err != nil {
log.Fatal(err.Error())
}
fmt.Println("Id: ", result.Id)
for index, ri := range result.RelatedItems {
fmt.Printf("Key: %d\n", index)
fmt.Printf("RID: %s\n", ri.RId)
}
I'm working on a Go wrapper for an API and I noticed that two of the JSON fields stay empty when they don't have any data.
Basically the API returns a set of information on a given url, and if it was visited at least once, everything is okay and I get a full json that I then Unmarshal into a struct:
{
"stats":{
"status":1,
"date":"09.07.2019",
"title":"Test",
"devices":{
"dev":[
{
"tag":"Desktop"
}
],
"sys":[
{
"tag":"GNU/Linux "
},
{
"tag":"Windows 10"
}
],
"bro":[
{
"tag":"Firefox 67.0"
},
{
"tag":"Chrome 62.0"
}
]
},
"refs":[
{
"link":"www.google.com"
}
]
}
}
This is the struct I'm using:
type Stats struct {
Stats struct {
Status int `json:"status"`
Date string `json:"date"`
Title string `json:"title"`
Devices struct {
Dev []struct {
Tag string `json:"tag"`
} `json:"dev"`
Sys []struct {
Tag string `json:"tag"`
} `json:"sys"`
Bro []struct {
Tag string `json:"tag"`
} `json:"bro"`
} `json:"devices"`
Refs []struct {
Link string `json:"link"`
} `json:"refs"`
} `json:"stats"`
}
When a new url is given, then things become a little bit weird:
{
"stats": {
"status": 1,
"date": "09.07.2019",
"title": "Test2",
"devices": [
],
"refs": [
]
}
}
As you can see, the fields "dev", "sys" and "bro" just disappear because they're not used and when I try to Unmarshal the JSON into the same struct I get json: cannot unmarshal array into Go struct field Stats.device of type [...]
I tried to use two different structs to handle both the responses but I'm sure that there's a way to handle them gracefully with just one.
Any help would be appreciated, thanks!
I finally managed to make it work with an ugly workaround.
I changed my struct to
type Stats struct {
Status int `json:"status"`
Date string `json:"date"`
Title string `json:"title"`
Devices interface{} `json:"devices"`
Refs interface{} `json:"refs"`
}
Then I can finally Unmarshal the JSON in both cases, but I get a map[string]interface{} when an object is passed and an empty interface{} when an empty array is passed. In order to fix this inconsistency, I simply check for the data type and force the use of a JSON intermediate conversion in order to unpack the map[string]interface{} value inside a custom Devices struct:
// Devices contains devices information
type Devices struct {
Dev []struct {
Tag string `json:"tag"`
Clicks string `json:"clicks"`
} `json:"dev"`
Sys []struct {
Tag string `json:"tag"`
Clicks string `json:"clicks"`
} `json:"sys"`
Bro []struct {
Tag string `json:"tag"`
Clicks string `json:"clicks"`
} `json:"bro"`
}
The algorithms I use are the following:
//ForceDevicesToRightType uses a json conversion as intermediary for filling the Stats.Devices
// struct with map[string]interface{} values
func ForceDevicesToRightType(dev interface{}) (Devices, error) {
temp, err := json.Marshal(dev)
if err != nil {
return Devices{}, err
}
// Use a temporary variable of the right type
var devices Devices
err = json.Unmarshal(temp, &devices)
if err != nil {
return Devices{}, err
}
return devices, nil
}
// ForceRefsToRightType uses a json conversion as intermediary for filling the Stats.Refs
// struct with map[string]interface{} values
func ForceRefsToRightType(refs interface{}) (Refs, error) {
temp, err := json.Marshal(refs)
if err != nil {
return Refs{}, err
}
// Use a temporary variable of the right type
var references Refs
err = json.Unmarshal(temp, &references)
if err != nil {
return Refs{}, err
}
return references, nil
}
Since the compiler knows that both Devices and Refs fields are interface{} I cannot simply access any methods after the conversion, so I simply make a cast of the right type and everything works fine.
For example, if I wanted to access the Dev sub-struct, this is the proper way:
y, _ := GetStats()
fmt.Println(y.Devices.(Devices).Dev)
It's ugly, but it works.
Thank you very much for your help, I hope that this method will save you an headache!
I'm trying to convert a JSON that contains only 1 field which apparently an array to a complex struct in Golang but unfortunately I'm not getting the data back, instead, I got:
{Result:[]}
Anyone knows why? (code below)
package main
import (
"encoding/json"
"fmt"
)
type Account struct {
AccountId string
}
type Response struct {
Result []Account
}
func main() {
input := []byte(`{
"result": [
{"account_id" : "1"},
{"account_id" : "2"},
{"account_id" : "3"},
]
}
`)
var resp Response
json.Unmarshal(input, &resp)
fmt.Printf("%+v\n", resp)
}
use a explicit tag in your stucture type.
type Account struct {
AccountId string `json:"account_id, omitempty"`
}
If you are a novice, keep in mind the JSON size, if is large then use a stream library (jstream or easyjson etc),
other advice is check nullables or omit when they are empty anyway you can use nullable library like https://github.com/guregu/null
Cheers!
I have a JSON string I want to unmarshal:
{
"id":1720,
"alertId":1,
"alertName":"{stats} Test Lambda Alert",
"dashboardId":5,
"panelId":2,
"userId":0,
"newState":"alerting",
"prevState":"ok",
"time":1523983581000,
"text":"",
"regionId":0,
"tags":[],
"login":"",
"email":"",
"avatarUrl":"",
"data":{
"evalMatches":[
{
"metric":"{prod}{stats} Lambda Alert Test",
"tags":null,
"value":16.525333333333332
}
]
}
}
I get the raw stream via a request: bodyBytes, err := ioutil.ReadAll(resp.Body)
I was hoping I could just specify a struct that pulls the values I care about, e.g.,
type Result struct {
ID string `json:"id"`
Time int64 `json:"time"`
}
However, when I try this, I get errors.
type Result struct {
ID string `json:"id"`
Time string `json:"time"`
}
var result Result
err2 := json.Unmarshal(bodyBytes, &result)
if err2 != nil {
log.Fatal(fmt.Sprintf(`Error Unmarshalling: %s`, err2))
}
fmt.Println(result.ID)
Error Unmarshalling: json: cannot unmarshal array into Go value of type main.Result
I suspect this error may be due to what's actually returned from ioutil.ReadAll(), since it has the above JSON string wrapped in [ ] if I do a fmt.Println(string(bodyBytes)), but if I try to json.Unmarshal(bodyBytes[0], &result), I just get compile errors, so I'm not sure.
If I want to unmarshal a JSON string, do I have to specify the full structure in my type Result struct? Is there a way around this? I don't want to be bound to the JSON object I receive (if the API changes upstream, it requires us to modify our code to recognize that, etc.).
You can unmarshal into structs that represent only some fields of your JSON document, but the field types have to match, as the error clearly states:
cannot unmarshal number into Go struct field Result.id of type string
You cannot unmarshal a number into a string. If you define the ID field as any numeric type it'll work just fine:
package main
import (
"encoding/json"
"fmt"
)
var j = []byte(`
{
"id":1720,
"prevState":"ok",
"time":1523983581000,
"text":"",
"regionId":0
}
`)
type Result struct {
ID int `json:"id"` // or any other integer type, or float{32,64}, or json.Number
Time int64 `json:"time"`
}
func main() {
var r Result
err := json.Unmarshal(j, &r)
fmt.Println(r, err)
}
Try it on the playground: https://play.golang.org/p/lqsQwLW2dHZ
Update
You have just edited your question with the actual error you receive. You have to unmarshal JSON arrays into slices. So if the HTTP response in fact returns a JSON array, unmarshal into []Result:
var j = []byte(`
[
{
"id":1720,
"prevState":"ok",
"time":1523983581000,
"text":"",
"regionId":0
}
]
`)
var r []Result
err := json.Unmarshal(j, &r)
fmt.Println(r[0], err)
https://play.golang.org/p/EbOVA8CbcFO
To generate Go types that match your JSON document pretty well, use https://mholt.github.io/json-to-go/.
I'm calling a REST API from my Go program which takes n number of hotel ids in the request and returns their data as a JSON. The response is like the following when say I pass 2 ids in the request, 1018089108070373346 and 2017089208070373346 :
{
"data": {
"1018089108070373346": {
"name": "A Nice Hotel",
"success": true
},
"2017089208070373346": {
"name": "Another Nice Hotel",
"success": true
}
}
}
Since I'm new to Golang I using a JSON Go tool available at http://mholt.github.io/json-to-go/ to get the struct representation for the above response. What I get is:
type Autogenerated struct {
Data struct {
Num1017089108070373346 struct {
Name string `json:"name"`
Success bool `json:"success"`
} `json:"1017089108070373346"`
Num2017089208070373346 struct {
Name string `json:"name"`
Success bool `json:"success"`
} `json:"2017089208070373346"`
} `json:"data"`
}
I cannot use the above struct because the actual id values and the number of ids I pass can be different each time, the JSON returned will have different keys. How can this situation be mapped to a struct ?
Thanks
Use a map:
type Item struct {
Name string `json:"name"`
Success bool `json:"success"`
}
type Response struct {
Data map[string]Item `json:"data"`
}
Run it on the playground
Here is some sample code that utilizes Mellow Marmots answer and shows how to iterate over the items in the response.
test.json
{
"data": {
"1018089108070373346": {
"name": "A Nice Hotel",
"success": true
},
"2017089208070373346": {
"name": "Another Nice Hotel",
"success": true
}
}
}
test.go
package main
import (
"encoding/json"
"fmt"
"os"
)
// Item struct
type Item struct {
Name string `json:"name"`
Success bool `json:"success"`
}
// Response struct
type Response struct {
Data map[string]Item `json:"data"`
}
func main() {
jsonFile, err := os.Open("test.json")
if err != nil {
fmt.Println("Error opening test file\n", err.Error())
return
}
jsonParser := json.NewDecoder(jsonFile)
var filedata Response
if err = jsonParser.Decode(&filedata); err != nil {
fmt.Println("Error while reading test file.\n", err.Error())
return
}
for key, value := range filedata.Data {
fmt.Println(key, value.Name, value.Success)
}
}
Which outputs:
1018089108070373346 A Nice Hotel true
2017089208070373346 Another Nice Hotel true