code: func (q *Query) WherePK() *Query {
  	if !q.hasModel() {
  		q.err(errModelNil)
  		return q
  	}
  
  	if err := q.model.Table().checkPKs(); err != nil {
  		q.err(err)
  		return q
  	}
  
  	q.where = append(q.where, wherePKQuery{q})
  	return q
  }
docs: // WherePK adds condition based on the model primary keys.
  // Usually it is the same as:
  //
  //    Where("id = ?id")