code: func (auup *AuthUserUserPermission) Insert(db XODB) error {
  	var err error
  
  	// if already exist, bail
  	if auup._exists {
  		return errors.New("insert failed: already exists")
  	}
  
  	// sql insert query, primary key provided by autoincrement
  	const sqlstr = `INSERT INTO django.auth_user_user_permissions (` +
  		`user_id, permission_id` +
  		`) VALUES (` +
  		`?, ?` +
  		`)`
  
  	// run query
  	XOLog(sqlstr, auup.UserID, auup.PermissionID)
  	res, err := db.Exec(sqlstr, auup.UserID, auup.PermissionID)
  	if err != nil {
  		return err
  	}
  
  	// retrieve id
  	id, err := res.LastInsertId()
  	if err != nil {
  		return err
  	}
  
  	// set primary key and existence
  	auup.ID = int(id)
  	auup._exists = true
  
  	return nil
  }
docs: // Insert inserts the AuthUserUserPermission to the database.