How can i add enum in gorm?

Question

I am writing PostgreSQL table schema.

type TestTable struct {
    ID        int    `gorm:"column:id;primaryKey;autoIncrement"`
    CarType   string `gorm:"column:car_type"`
}

So how can i add car types like "SEDAN", "HATCHBACK", "MINIVAN" as enum data type

Answer 1

Assuming you are using GORM. First in your database create a type.

CREATE TYPE car_type AS ENUM (
    'SEDAN',
    'HATCHBACK',
    'MINIVAN');

Then you will need to define the following model:

type carType string

const (
    SEDAN  carType = "SEDAN"
    HATCHBACK carType = "HATCHBACK"
    MINIVAN carType = "MINIVAN"
)

func (ct *carType) Scan(value interface{}) error {
    *ct = carType(value.([]byte))
    return nil
}

func (ct carType) Value() (driver.Value, error) {
    return string(ct), nil
}

type MyTable struct {
    gorm.Model
    CarType carType `sql:"car_type"`
}

func (MyTable) TableName() string {
    return "my_table"
}

Answer 2

in order to extend Nick's answer I am adding the following for automation:

Assuming you have DBClient struct, you can create a method that creates this car type:

func (psqlClient *DBClient) CreateCarTypeEnum() error {
    result := psqlClient.db.Exec("SELECT 1 FROM pg_type WHERE typname = 'car_type';")

    switch {
    case result.RowsAffected == 0:
        if err := psqlClient.db.Exec("CREATE TYPE car_type AS ENUM ('SEDAN', 'HATCHBACK', 'MINIVAN');").Error; err != nil {
            log.Error().Err(err).Msg("Error creating car_type ENUM")
            return err
        }

        return nil
    case result.Error != nil:
        return result.Error

    default:
        return nil
    }
}

Answer 3

on a side note- if you decide to go with slightly different approach: you can define your enums as int, and leverage iota. then you can use code generator to create sql Scaner/Valuer but also json/text representations. for example: https://github.com/dmarkham/enumer