Unmarshal JSON with many layers of nested maps - json

Question

I realize that this question is very similar to others on stackoverflow but I have not been able to model the other questions to my use case.
I have JSON that looks like this (simplified for this post)
{
"somekey": "string",
"state": {
"groups": {
"host:host1": {
"status": "OK",
"morethings": "blah"
},
"host:host2": {
"status": "Alert",
"morethings": "blah"
}
}
}
}
I am trying to get the hashes under groups into an array so I can iterate through and check the status of the hosts.
Based on some of the other posts here I felt I was on the correct track with this example:
package main
import (
"encoding/json"
"fmt"
)
const jsonStream = `
{
"state": {
"groups": {
"host:i-b3a6cea5": {
"status": "OK",
"last_triggered_ts": null,
"last_nodata_ts": null,
"name": "host:i-b3a6cea5",
"last_notified_ts": null,
"last_resolved_ts": null
},
"host:i-4d81ca7c": {
"status": "OK",
"last_triggered_ts": null,
"last_nodata_ts": null,
"name": "host:i-4d81ca7c",
"last_notified_ts": null,
"last_resolved_ts": null
},
"host:i-a03a7758": {
"status": "Alert",
"triggering_value": {
"to_ts": 1475092440,
"value": 2,
"from_ts": 1475092380
},
"last_triggered_ts": 1475092440,
"last_nodata_ts": null,
"name": "host:i-a03a7758",
"last_notified_ts": 1475092440,
"last_resolved_ts": null
}
}
}
}`
type hostDetails struct {
Status string `json:"status"`
Name string `json:"name"`
}
type GroupsData struct {
Groups map[string]hostDetails `json:"groups"`
}
type Data struct {
State map[string]GroupsData `json:"state"`
}
func main() {
var data Data
err := json.Unmarshal([]byte(jsonStream), &data)
if err != nil {
fmt.Println(err)
}
fmt.Println(data)
}
but I only end up with an empty data structure:
{map[groups:{map[]}]}
To see if I was even on the correct track I modified my JSON and took out the state key so that groups was the at the top level.
When I do that it populates the data structure as seen here
I'm struggling to understand why I can deal with the 1 level of nesting but not the second level?
My caveman brain thinks I should be able to reuse the pattern for as many levels of nesting I have.
At this point I've been fiddling most of the day and feel like I'm missing something that's right in front of me but can't see it.
Any pointers would be appreciated on how to handle the additional layer of nesting.

Answer 1

1 - You may remove one extra level by using:
var data map[string]GroupsData
Try it on The Go Playground:
package main
import (
"encoding/json"
"fmt"
)
func main() {
var data map[string]GroupsData
err := json.Unmarshal([]byte(jsonStream), &data)
if err != nil {
fmt.Println(err)
}
fmt.Println(data)
}
type GroupsData struct {
Groups map[string]HostDetails `json:"groups"`
}
type HostDetails struct {
Status string `json:"status"`
Name string `json:"name"`
}
const jsonStream = `
{
"state": {
"groups": {
"host:i-b3a6cea5": {
"status": "OK",
"last_triggered_ts": null,
"last_nodata_ts": null,
"name": "host:i-b3a6cea5",
"last_notified_ts": null,
"last_resolved_ts": null
},
"host:i-4d81ca7c": {
"status": "OK",
"last_triggered_ts": null,
"last_nodata_ts": null,
"name": "host:i-4d81ca7c",
"last_notified_ts": null,
"last_resolved_ts": null
},
"host:i-a03a7758": {
"status": "Alert",
"triggering_value": {
"to_ts": 1475092440,
"value": 2,
"from_ts": 1475092380
},
"last_triggered_ts": 1475092440,
"last_nodata_ts": null,
"name": "host:i-a03a7758",
"last_notified_ts": 1475092440,
"last_resolved_ts": null
}
}
}
}`
output:
map[state:{map[host:i-b3a6cea5:{OK host:i-b3a6cea5} host:i-4d81ca7c:{OK host:i-4d81ca7c} host:i-a03a7758:{Alert host:i-a03a7758}]}]
2 - You may use:
type Data struct {
State GroupsData `json:"state"`
}
Try it on The Go Playground:
package main
import (
"encoding/json"
"fmt"
)
func main() {
var data Data
err := json.Unmarshal([]byte(jsonStream), &data)
if err != nil {
fmt.Println(err)
}
fmt.Println(data)
}
type Data struct {
State GroupsData `json:"state"`
}
type GroupsData struct {
Groups map[string]hostDetails `json:"groups"`
}
type hostDetails struct {
Status string `json:"status"`
Name string `json:"name"`
}
const jsonStream = `
{
"state": {
"groups": {
"host:i-b3a6cea5": {
"status": "OK",
"last_triggered_ts": null,
"last_nodata_ts": null,
"name": "host:i-b3a6cea5",
"last_notified_ts": null,
"last_resolved_ts": null
},
"host:i-4d81ca7c": {
"status": "OK",
"last_triggered_ts": null,
"last_nodata_ts": null,
"name": "host:i-4d81ca7c",
"last_notified_ts": null,
"last_resolved_ts": null
},
"host:i-a03a7758": {
"status": "Alert",
"triggering_value": {
"to_ts": 1475092440,
"value": 2,
"from_ts": 1475092380
},
"last_triggered_ts": 1475092440,
"last_nodata_ts": null,
"name": "host:i-a03a7758",
"last_notified_ts": 1475092440,
"last_resolved_ts": null
}
}
}
}`
output:
{{map[host:i-b3a6cea5:{OK host:i-b3a6cea5} host:i-4d81ca7c:{OK host:i-4d81ca7c} host:i-a03a7758:{Alert host:i-a03a7758}]}}
Your code works with one extra level "state": {} in JSON data: The Go Playground

Answer 2

Your mistake is that Data.State shouldn't be a map. If you change the definition to
type Data struct {
State GroupsData `json:"state"`
}
it works: https://play.golang.org/p/oRjSJMDzU8.