How to Add Choices to database field using GORM - database

Question

I'm very new to Golang as I mostly code in Python, so came across one problem that I'm not able to solve. I want to add choices to a field in Golang Struct via GORM or any other way if I can achieve that.
My model looks like this
type User struct{
FirstName string `gorm:"size:100" json:"first_name"`
LastName string `gorm:"size:100" json:"last_name"`
Email *string `gorm:"size:250;index;not null;index:email;unique" json:"email"`
Role string `gorm:"default:User;not null" json:"is_active"` // TODO Add Choice
}
I want to add choices to my Role Field in User Models from ['Admin', 'User', 'Guest']. Is there a way to achieve it using GORM or any other method that will solve my problem? I can make it a Foreign key if there is no direct way to do it. I'm using PostgreSQL to store tables. Thanks in Advance!

Answer 1

Assuming you have a one-to-one relation between roles and users, one approach with the foreign keys would be something like this:
type User struct{
ID int64 `json:"id"`
FirstName string `gorm:"size:100" json:"first_name"`
LastName string `gorm:"size:100" json:"last_name"`
Email *string `gorm:"size:250;index;not null;index:email;unique" json:"email"`
RoleID int64 `json:"role_id"`
Role *Role `json:"role"`
}
type Role struct {
ID int64 `json:"id"`
Name string `json:"name"`
}
//load data
var users []User
err := db.Preload("Role").Find(&users).Error
EDIT: solution for many-to-many
relationship
Assuming that you would have a table like users_roles that links the users and roles tables, one solution might look like this:
type User struct{
ID int64 `json:"id"`
FirstName string `gorm:"size:100" json:"first_name"`
LastName string `gorm:"size:100" json:"last_name"`
Email *string `gorm:"size:250;index;not null;index:email;unique" json:"email"`
Roles []*Role `gorm:"many2many:users_roles;" json:"roles"`
}
type Role struct {
ID int64 `json:"id"`
Name string `json:"name"`
}
//load data
var users []User
err := db.Preload("Roles").Find(&users).Error

Answer 2

For PostGreSQL First create enum manually in your database
CREATE TYPE user_access AS ENUM (
'admin',
'user'
);
Then
type Role string
const (
Admin Role = "admin"
User Role = "user"
)
func (r *Role) Scan(value interface{}) error {
*r = Role(value.([]byte))
return nil
}
func (r Role) Value() (driver.Value, error) {
return string(r), nil
}
type User struct{
ID int64 `json:"id"`
FirstName string `gorm:"size:100" json:"first_name"`
LastName string `gorm:"size:100" json:"last_name"`
Email *string `gorm:"size:250;index;not null;index:email;unique" json:"email"`
Role Role `sql:"type:user_access"` // PostGreSQL
Role Role `json:"role" sql:"type:ENUM('admin', 'user')"` // MySQL
}
For more info you can check github issue and doc