Using GORM with custom join table and foreign keys

I'm using GORM to create database models. I have three models that I am having troubles with. There are User, Email, and UserEmail models. I want a many2many relationship between the User and Email models, so that I can keep track of when a users change an email and when, without having to use log table. Since the UserEmail model exists, I see no reason for the User model to hold an EmailID. Otherwise, the UserEmail just becomes a typical log table.

The UserEmail table should only allow any User to have one email set at a time. For that reason, I want to se the UserID + DeletedAt fields to be the primary key. That way, only one row with a NULL DeletedAt can exist.

The problem I am having is that the migrator commands I am running is causing multiple errors. I've tried so many other things that cannot recount everything, however the other things I have tried wouldn't properly produce the correct foreign keys. I think I want two foreign keys in UserEmail for EmailID and UserID. I would also like GORM's Preload functionality should work if possible.

I have a migrate command, that when run, it essentially runs this:

func main() {
app.DB.Migrator().DropTable(&User{})
app.DB.Migrator().CreateTable(&User{})
app.DB.Migrator().DropTable(&Email{})
app.DB.Migrator().CreateTable(&Email{})
app.DB.Migrator().DropTable(&UserEmail{})
app.DB.Migrator().CreateTable(&UserEmail{})
}

I have also tried migrating each model in different orders. However every time, I get errors. The Email and UserEmail tables get created properly, however User always has some errors.

2023/07/21 16:38:50 Dropping table named 'users'...
2023/07/21 16:38:50 [...]/go/pkg/mod/gorm.io/driver/mysql@v1.3.6/migrator.go:126
[error] invalid field found for struct github.com/neekla/pmapi/api/database/model.User's field Email: define a valid foreign key for relations or implement the Valuer/Scanner interface
2023/07/21 16:38:50 [...]/go/pkg/mod/gorm.io/driver/mysql@v1.3.6/migrator.go:126
[error] failed to parse value &model.User{ID:0x0, Email:model.Email{ID:0x0, Address:"", IsBanned:false, IsRegistered:false, IsVerified:false, CreatedAt:time.Date(1, time.January, 1, 0, 0, 0, 0, time.UTC), UpdatedAt:time.Date(1, time.January, 1, 0, 0, 0, 0, time.UTC), DeletedAt:(*gorm.DeletedAt)(nil)}, PreviousEmails:[]model.Email(nil), Name:"", PasswordHash:"", CreatedAt:time.Date(1, time.January, 1, 0, 0, 0, 0, time.UTC), UpdatedAt:time.Date(1, time.January, 1, 0, 0, 0, 0, time.UTC), DeletedAt:(*gorm.DeletedAt)(nil)}, got error invalid field found for struct github.com/neekla/pmapi/api/database/model.User's field Email: define a valid foreign key for relations or implement the Valuer/Scanner interface
2023/07/21 16:38:50 [...]/go/pkg/mod/gorm.io/driver/mysql@v1.3.6/migrator.go:128
[0.515ms] [rows:0] SET FOREIGN_KEY_CHECKS = 0;
2023/07/21 16:38:50 [...]/go/pkg/mod/gorm.io/driver/mysql@v1.3.6/migrator.go:130
[error] invalid field found for struct github.com/neekla/pmapi/api/database/model.User's field Email: define a valid foreign key for relations or implement the Valuer/Scanner interface
2023/07/21 16:38:50 Creating table named 'users'...
2023/07/21 16:38:50 [...]/api/command/commandMigrate.go:132
[error] invalid field found for struct github.com/neekla/pmapi/api/database/model.User's field Email: define a valid foreign key for relations or implement the Valuer/Scanner interface
2023/07/21 16:38:50 [...]/api/command/commandMigrate.go:132
[error] failed to parse value &model.User{ID:0x0, Email:model.Email{ID:0x0, Address:"", IsBanned:false, IsRegistered:false, IsVerified:false, CreatedAt:time.Date(1, time.January, 1, 0, 0, 0, 0, time.UTC), UpdatedAt:time.Date(1, time.January, 1, 0, 0, 0, 0, time.UTC), DeletedAt:(*gorm.DeletedAt)(nil)}, PreviousEmails:[]model.Email(nil), Name:"", PasswordHash:"", CreatedAt:time.Date(1, time.January, 1, 0, 0, 0, 0, time.UTC), UpdatedAt:time.Date(1, time.January, 1, 0, 0, 0, 0, time.UTC), DeletedAt:(*gorm.DeletedAt)(nil)}, got error invalid field found for struct github.com/neekla/pmapi/api/database/model.User's field Email: define a valid foreign key for relations or implement the Valuer/Scanner interface
2023/07/21 16:38:50 [...]/api/command/commandMigrate.go:132
[error] invalid field found for struct github.com/neekla/pmapi/api/database/model.User's field Email: define a valid foreign key for relations or implement the Valuer/Scanner interface

Here is what the current models look like, which gives a glimpse the desired functionality.

func init() {
app.DB.SetupJoinTable(&User{}, "Emails", &UserEmail{})
}
// the user table should not have any EmailID column, that's what the UserEmail table is for, but it would be nice to still be able to preload the email values
// Email field should be the email in UserEmails that has NULL for for DeletedAt
// PreviousEmails field should be all the emails in UserEmails that have a non-NULL DeletedAt
type User struct {
ID             uint            `json:"id" gorm:"primarykey"`
Email          Email           `json:"email"`
PreviousEmails []Email         `json:"previous_emails"`
Name           string          `json:"name" gorm:"type:varchar(255);not null"`
PasswordHash   string          `json:"password_hash,omitempty" gorm:"type:binary(60);not null"`
CreatedAt      time.Time       `json:"created_at" gorm:"type:DATETIME;default:CURRENT_TIMESTAMP;not null"`
UpdatedAt      time.Time       `json:"updated_at" gorm:"type:DATETIME"`
DeletedAt      *gorm.DeletedAt `json:"deleted_at" gorm:"type:DATETIME;index"`
}
func (User) TableName() string {
return "users"
}

// emails do not get deleted, they are permanently stored
type Email struct {
ID           uint            `json:"id" gorm:"primarykey"`
Address      string          `json:"address" gorm:"type:varchar(320);unique;not null"`
IsBanned     bool            `json:"is_banned" gorm:"type:bit;default:0;not null"`
IsRegistered bool            `json:"is_registered" gorm:"type:bit;default:0;not null"`
IsVerified   bool            `json:"is_verified" gorm:"type:bit;default:0;not null"`
CreatedAt    time.Time       `json:"created_at" gorm:"type:DATETIME;default:CURRENT_TIMESTAMP;not null"`
UpdatedAt    time.Time       `json:"updated_at" gorm:"type:DATETIME"`
}
func (Email) TableName() string {
return "emails"
}

// when a user changes their email, the old one gets soft deleted
type UserEmail struct {
EmailID   uint            `json:"email_id"`
UserID    uint            `json:"user_id" gorm:"primarykey"`
CreatedAt time.Time       `json:"created_at" gorm:"type:DATETIME;default:CURRENT_TIMESTAMP;not null"`
DeletedAt *gorm.DeletedAt `json:"deleted_at" gorm:"primarykey;type:DATETIME"`
}
func (UserEmail) TableName() string {
return "user_emails"
}

How can I achieve the desired effects?

I fixed it. It was simple. All I had to do was run:

go get gorm.io/gorm@none