How to insert a map[string] into a jsonb field - postgresql

Question

I have a struct Huygens:
type Huygens struct {
Worlds map[string]World `json:"worlds" sql:"type:JSONB"`
}
type World struct {
Diameter int
Name string
}
When I try to insert into a Postgres DB using GORM I get:
sql: converting argument $1 type: unsupported type map[string]huygens.world, a map
To insert I simply use db.Create(&World{})
Does anyone know how to insert that column as a JSONB column and avoid that error?
Thanks

Answer 1

You need to specify that Huygens is a gorm.Model and dump your World struct to a []byte type.
import (
"encoding/json"
"fmt"
"gorm.io/datatypes"
)
type Huygens struct {
gorm.Model
Worlds datatypes.JSON
}
type World struct {
Diameter int
Name string
}
world := World{Diameter: 3, Name: Earth}
b, err := json.Marshal(world)
if err != nil {
fmt.Println("error:", err)
}
db.Create(&Huygens{Worlds: datatypes.JSON(b)})
You can see more here.

Answer 2

Another way, which makes the model more usable, is to create a type that implements Scan/Value, and in those Unmarshal from/Marshal to JSON:
type Huygens struct {
Worlds WorldsMap `json:"worlds"`
}
type World struct {
Diameter int
Name string
}
type WorldsMap map[string]World
func (WorldsMap) GormDataType() string {
return "JSONB"
}
func (w *WorldsMap) Scan(value interface{}) error {
var bytes []byte
switch v := value.(type) {
case []byte:
bytes = v
case string:
bytes = []byte(v)
default:
return errors.New(fmt.Sprint("Failed to unmarshal JSONB value:", value))
}
err := json.Unmarshal(bytes, w)
return err
}
func (w WorldsMap) Value() (driver.Value, error) {
bytes, err := json.Marshal(s)
return string(bytes), err
}
Then you can use the Worlds field in your code like a map, as opposed to an awkward byte slice.