yii getter/setter

getset.php

<?php

class MyClass extends \yii\base\Component
{
    private $_value;

    public function getValue()
    {
        if ($this->_value === null) {
            $this->_value = /* your sql query here */;
        }
        return $this->_value;
    }

    // setter is optional, if not present, this will be a read only property
    public function setValue($value)
    {
          $this->_value = $value;
    }
}