Why can this data not be properly unmarshalled into my object model? - json

Question

I have a (non)working example here: https://play.golang.org/p/qaYhKvJ65J3
I'm not sure why the following data:
alertData := `{
"Id": 0,
"Version": 0,
"OrgId": 1,
"DashboardId": 61,
"PanelId": 84,
"Name": "{qa-dev}{stats-pipeline} Topology Message Age (aggregator) alert",
"Message": "",
"Severity": "",
"State": "",
"Handler": 1,
"Silenced": false,
"ExecutionError": "",
"Frequency": 10,
"EvalData": null,
"NewStateDate": "0001-01-01T00:00:00Z",
"PrevStateDate": "0001-01-01T00:00:00Z",
"StateChanges": 0,
"Created": "0001-01-01T00:00:00Z",
"Updated": "0001-01-01T00:00:00Z",
"Settings": {
"conditions": [
{
"evaluator": {
"params": [
10000
],
"type": "gt"
},
"operator": {
"type": "and"
},
"query": {
"datasourceId": 2,
"model": {
"hide": true,
"refCount": 0,
"refId": "C",
"textEditor": false
},
"params": [
"C",
"5m",
"now"
]
},
"reducer": {
"params": [],
"type": "avg"
},
"type": "query"
}
],
"executionErrorState": "keep_state",
"frequency": "10s",
"handler": 1,
"name": "{qa-dev}{stats-pipeline} Topology Message Age (aggregator) alert",
"noDataState": "keep_state",
"notifications": []
}
}`
Can't be unmarshalled into the following object model:
type Condition struct {
Evaluator struct {
Params []int `json:"params"`
Type string `json:"type"`
} `json:"evaluator"`
Operator struct {
Type string `json:"type"`
} `json:"operator"`
Query struct {
Params []string `json:"params"`
} `json:"query"`
Reducer struct {
Params []interface{} `json:"params"`
Type string `json:"type"`
} `json:"reducer"`
Type string `json:"type"`
}
When I do the following:
condition := Condition{}
err := json.Unmarshal([]byte(alertData), &condition)
if err != nil {
panic(err)
}
fmt.Printf("\n\n json object:::: %+v", condition)
I just get: json object:::: {Evaluator:{Params:[] Type:} Operator:{Type:} Query:{Params:[]} Reducer:{Params:[] Type:} Type:}
Ideally I'd be able to parse it into something like type Conditions []struct{ } but I'm not sure if you can define models as lists?

Answer 1

It looks like you are trying to access the "conditions" property nested under the root "Settings" property. As such, you need to define that root-level type and enough fields to tell the unmarshaler how to find your target property. As such, you would just need to create a new "AlertData" type with the necessary "Settings/conditions" fields.
For example (Go Playground):
type AlertData struct {
Settings struct {
Conditions []Condition `json:"conditions"`
}
}
func main() {
alert := AlertData{}
err := json.Unmarshal([]byte(alertData), &alert)
if err != nil {
panic(err)
}
fmt.Printf("OK: conditions=%#v\n", alert.Settings.Conditions)
// OK: conditions=[]main.Condition{main.Condition{Evaluator:struct { Params []int "json:\"params\""; Type string "json:\"type\"" }{Params:[]int{10000}, Type:"gt"}, Operator:struct { Type string "json:\"type\"" }{Type:"and"}, Query:struct { Params []string "json:\"params\"" }{Params:[]string{"C", "5m", "now"}}, Reducer:struct { Params []interface {} "json:\"params\""; Type string "json:\"type\"" }{Params:[]interface {}{}, Type:"avg"}, Type:"query"}}
}
Note that the printed listing includes so much type information because the "Condition" type uses anonymous structs as field types. If you were to extract them into named structs it will be easier to work with the data, e.g.:
type Condition struct {
Evaluator Evaluator `json:"evaluator"`
Operator Operator `json:"operator"`
// ...
}
type Evaluator struct {
Params []int `json:"params"`
Type string `json:"type"`
}
type Operator struct {
Type string `json:"type"`
}
//...
// OK: conditions=[]main.Condition{
// main.Condition{
// Evaluator:main.Evaluator{Params:[]int{10000}, Type:"gt"},
// Operator:main.Operator{Type:"and"},
// Query:main.Query{Params:[]string{"C", "5m", "now"}},
// Reducer:main.Reducer{Params:[]interface {}{}, Type:"avg"},
// Type:"query",
// },
// }
Go Playground example here...

Answer 2

Maerics explanation is correct, here is an alternative approach which wraps access around struct methods, the data structure is also fully defined. If you're new to Go it's good to get handle on creating the data structures yourself, but here is a handy utility for helping create structs from valid JSON
https://mholt.github.io/json-to-go/
package main
import (
"encoding/json"
"fmt"
"log"
"time"
)
type Data struct {
ID int `json:"Id"`
Version int `json:"Version"`
OrgID int `json:"OrgId"`
DashboardID int `json:"DashboardId"`
PanelID int `json:"PanelId"`
Name string `json:"Name"`
Message string `json:"Message"`
Severity string `json:"Severity"`
State string `json:"State"`
Handler int `json:"Handler"`
Silenced bool `json:"Silenced"`
ExecutionError string `json:"ExecutionError"`
Frequency int `json:"Frequency"`
EvalData interface{} `json:"EvalData"`
NewStateDate time.Time `json:"NewStateDate"`
PrevStateDate time.Time `json:"PrevStateDate"`
StateChanges int `json:"StateChanges"`
Created time.Time `json:"Created"`
Updated time.Time `json:"Updated"`
Settings struct {
Conditions []Condition `json:"conditions"`
ExecutionErrorState string `json:"executionErrorState"`
Frequency string `json:"frequency"`
Handler int `json:"handler"`
Name string `json:"name"`
NoDataState string `json:"noDataState"`
Notifications []interface{} `json:"notifications"`
} `json:"Settings"`
}
type Condition struct {
Evaluator struct {
Params []int `json:"params"`
Type string `json:"type"`
} `json:"evaluator"`
Operator struct {
Type string `json:"type"`
} `json:"operator"`
Query struct {
DatasourceID int `json:"datasourceId"`
Model struct {
Hide bool `json:"hide"`
RefCount int `json:"refCount"`
RefID string `json:"refId"`
TextEditor bool `json:"textEditor"`
} `json:"model"`
Params []string `json:"params"`
} `json:"query"`
Reducer struct {
Params []interface{} `json:"params"`
Type string `json:"type"`
} `json:"reducer"`
Type string `json:"type"`
}
func (d Data) GetFirstCondition() (Condition, error) {
if len(d.Settings.Conditions) > 0 {
return d.Settings.Conditions[0], nil
}
return Condition{}, fmt.Errorf("no conditions found")
}
func (d Data) GetConditionByIndex(index uint) (Condition, error) {
if len(d.Settings.Conditions) == 0 {
return Condition{}, fmt.Errorf("no conditions found")
}
if int(index) > len(d.Settings.Conditions)-1 {
return Condition{}, fmt.Errorf("index out of bounds")
}
return d.Settings.Conditions[index], nil
}
var alertData = `{
"Id": 0,
"Version": 0,
"OrgId": 1,
"DashboardId": 61,
"PanelId": 84,
"Name": "{qa-dev}{stats-pipeline} Topology Message Age (aggregator) alert",
"Message": "",
"Severity": "",
"State": "",
"Handler": 1,
"Silenced": false,
"ExecutionError": "",
"Frequency": 10,
"EvalData": null,
"NewStateDate": "0001-01-01T00:00:00Z",
"PrevStateDate": "0001-01-01T00:00:00Z",
"StateChanges": 0,
"Created": "0001-01-01T00:00:00Z",
"Updated": "0001-01-01T00:00:00Z",
"Settings": {
"conditions": [
{
"evaluator": {
"params": [
10000
],
"type": "gt"
},
"operator": {
"type": "and"
},
"query": {
"datasourceId": 2,
"model": {
"hide": true,
"refCount": 0,
"refId": "C",
"textEditor": false
},
"params": [
"C",
"5m",
"now"
]
},
"reducer": {
"params": [],
"type": "avg"
},
"type": "query"
}
],
"executionErrorState": "keep_state",
"frequency": "10s",
"handler": 1,
"name": "{qa-dev}{stats-pipeline} Topology Message Age (aggregator) alert",
"noDataState": "keep_state",
"notifications": []
}
}`
func main() {
var res Data
err := json.Unmarshal([]byte(alertData), &res)
if err != nil {
log.Fatal(err)
}
fmt.Println(res.GetFirstCondition())
fmt.Println(res.GetConditionByIndex(0))
// should fail :-)
fmt.Println(res.GetConditionByIndex(1))
}