golang unmarshal using db tags - sql

Question

I have a sql query which fetches the list of cities nested inside provinces nested inside countries
SELECT
C.*,
P.provinces
FROM
countries AS C
LEFT JOIN (
SELECT
P.country_id,
json_agg(json_build_object(
'id', P.id,
'name', P.name,
'slug', P.slug,
'cities', Ci.cities
)) AS provinces
FROM
provinces AS P
LEFT JOIN (
SELECT
Ci.province_id,
json_agg(json_build_object(
'id', Ci.id,
'name', Ci.name,
'slug', Ci.slug
)) AS cities
FROM
cities AS Ci
GROUP BY Ci.province_id
) AS Ci ON Ci.province_id = P.id
GROUP BY P.country_id
) AS P ON P.country_id = C.id
I am fetching this data into slice of countries
type Country struct {
Id int64 `json:"id" db:"id"`
ISOCode2 string `json:"isoCode2" db:"iso_code_2"`
ISOCode3 string `json:"isoCode3" db:"iso_code_3"`
ISONumCode string `json:"isoNumCode" db:"iso_num_code"`
Name string `json:"name" db:"name"`
Slug string `json:"slug" db:"slug"`
Provinces SliceProvince `json:"provinces" db:"provinces"`
}
type SliceProvince []Province
func (provinces *SliceProvince) Scan(src any) (err error) {
if src == nil {
return
}
var source []byte
switch src := src.(type) {
case []byte:
source = src
case string:
source = []byte(src)
default:
return fmt.Errorf("unsupported type in scan:%v", src)
}
err = json.Unmarshal(source, provinces)
return
}
type Province struct {
Id int64 `json:"id" db:"id"`
Name string `json:"name" db:"name"`
Slug string `json:"slug" db:"slug"`
Cities SliceCity `json:"cities" db:"cities"`
}
type SliceCity []City
func (cities *SliceCity) Scan(src any) (err error) {
if src == nil {
return
}
var source []byte
switch src := src.(type) {
case []byte:
source = src
case string:
source = []byte(src)
default:
return fmt.Errorf("unsupported type in scan")
}
err = json.Unmarshal(source, cities)
return
}
type City struct {
Id int64 `json:"id" db:"id"`
Name string `json:"name" db:"name"`
Slug string `json:"slug" db:"slug"`
}
Now, my main query is that in the scan methods for these models, I want to do unmarshalling using db tags instead of json tags. Is there any workaround which I can do for this.
I came up with a thought of unmarshalling it to a map, then change their keys from db tag ones to json tag ones, then marshal and unmarshal it to the corresponding struct. But when there would be nesting of models, or slices involved, that would increase the complexity