Tell Gorm how to "read"/"write" an interface field in a struct

Imagine I have the following struct:

type User struct {
    ID   uuid.UUID
    Name string
    Hobbies []Hobby
}

where Hobby is an interface with several implementations, as an example:

type ReadingHobby struct {
    ID     uuid.UUID
    userID uuid.UUID
    User   *User
    Books  ...
}

type HikingHobby struct {
    ID     uuid.UUID
    userID uuid.UUID
    User   *User
    Routes ...
}

Each hobby is stored in its own table, so following the previous example, we would have a reading_hobby table, and a hiking_hobby table with their own table definition and foreign keys.

But then, when I try to load the Hobbies from an User using gorm, I get Unsopported Data type, which makes sense because gorm does not know how to serialize/deserialize that field.

How can I achieve that? I was checking to create my custom serializer (https://gorm.io/docs/serializer.html), but I don't have access to the db to "query" all the possible hobbies tables and get all the ones that belong to the user.

As a last solution I was thinking to use the AfterFind hook (https://gorm.io/docs/hooks.html#Querying-an-object), but I would also like to be able to use Preload("Hobbies") when I need the hobbies, instead of always retrieving them with the hook.

Any ideas?

Not sure if this would suit your needs, but I don't really see any easier way

I think I would go with two different models :

One reflecting the DB, with which you can more easily handle gorm :

type User struct {
    ID   uuid.UUID
    Name string
    ReadingHobbies []ReadingHobby
    HikingHobbies []HikingHobby
    ...
}

And your original struct with the interface :

type UserInterface struct {
    ID   uuid.UUID
    Name string
    Hobbies []Hobby
}

Then have a converter to the struct interfacing :

func (u User) ToInterface() UserInterface {
	return UserInterface{
        ID: u.ID,
        ...
    }
}