Use custom types in structs¶

SQLair makes it very easy to serialise to and from structs. But one case that may cause issues is when you have a user-defined type in your struct. For example:

type MyModel struct {
  ID  int    `db:"uuid"`
  Key *MyKey `db:"key"`
}

type MyKey [32]int

For this example, MyKey could be any user-defined type that can be serialised to a database row type. The problem is that SQLair and its underlying libraries do not know how to serialise the MyKey type.

Luckily, there are two very useful interfaces you can use to get around this problem: the Valuer and Scanner. The Valuer interface tells the driver how to serialise the type for putting in the database and the Scanner tells it how to deserialise it.

For example:

func (k *MyKey) Value() (driver.Value, error) {
  return k[:], nil
}

func (k *MyKey) Scan(src any) error {
  bs, ok := src.([]byte)
  if !ok {
    return fmt.Errorf("unexpected type %T", src)
  }
  if len(bs) != len(k) {
    return fmt.Errorf("invalid key found in db")
  }
  copy(k[:], bs) 
  return nil
}

Go | Valuer, Go | Scanner