Create user in database

db/user.go

@@ -0,0 +1,29 @@
+package db
+
+import (
+	"errors"
+
+	"gorm.io/gorm"
+)
+
+type User struct {
+	gorm.Model
+	Username string
+	Password string
+}
+
+var (
+	ERROR_USER_USERNAME_NOT_UNIQUE = errors.New("Username already persists in database")
+)
+
+func (u *User) BeforeCreate(ctx *gorm.DB) error {
+	var duplicate User
+	err := ctx.Find(&duplicate, User{Username: u.Username}).Error
+	if err != nil {
+		return err
+	}
+	if duplicate.ID != 0 {
+		return ERROR_USER_USERNAME_NOT_UNIQUE
+	}
+	return nil
+}