how to convert map[string]interface{} data to struct - json

Question

I do not know how to ask, so i will ask with an example.
I have some data like that
{
..
"velocityStatEntries": {
"8753": {
"estimated": {"value": 23.0,"text": "23.0"},
"completed": {"value": 27.0,"text": "27.0"}
},
"8673": {
"estimated": {"value": 54.5,"text": "54.5"},
"completed": {"value": 58.5,"text": "58.5"}
},
.
.
.
}
..
}
I want to declare a type that takes map key to its "KEY" or any property that is given by me.
Is it possible without using map iteration?
Expected output:
{...
"velocityStatEntries": {
{
"key": "8753",
"estimated": {"value": 54.5,"text": "54.5"},
"completed": {"value": 58.5,"text": "58.5"}
},
{
"key": "8673",
"estimated": {"value": 54.5,"text": "54.5"},
"completed": {"value": 58.5,"text": "58.5"}
},
}
...
}
This is what i have done
type VelocityStatEntry struct {
Key string
Estimated struct {
Value float64 `json:"value"`
Text string `json:"text"`
} `json:"estimated"`
Completed struct {
Value float64 `json:"value"`
Text string `json:"text"`
} `json:"completed"`
}
type RapidChartResponse struct {
...
VelocityStatEntries map[string]VelocityStatEntry `json:"velocityStatEntries"`
..
}
But it is not working. I want to take that string map key to KEY property.

Answer 1

If the data originates from JSON then you should skip the map[string]interface{} and instead use a custom unmarshaler implemented by your desired struct that does what you want. Perhaps by utilizing a map[string]json.RawMessage. But map[string]interface{} to struct conversion is a pain, avoid it if possible.
For example:
type VelocityStatEntryList []*VelocityStatEntry
func (ls *VelocityStatEntryList) UnmarshalJSON(data []byte) error {
var m map[string]json.RawMessage
if err := json.Unmarshal(data, &m); err != nil {
return err
}
for k, v := range m {
e := &VelocityStatEntry{Key: k}
if err := json.Unmarshal([]byte(v), e); err != nil {
return err
}
*ls = append(*ls, e)
}
return nil
}
https://go.dev/play/p/VcaW_BWXRVr