Repo/Dao/Account.php
public function updateBalance($accountId, $delta)
    {
        if ($delta < 0) {
            $exp = '(`' . Entity::A_BALANCE . '`-' . abs($delta) . ')';
        } else {
            $exp = '(`' . Entity::A_BALANCE . '`+' . abs($delta) . ')';
        }
        $exp = new \Praxigento\Core\App\Repo\Query\Expression($exp);
        $bind = [Entity::A_BALANCE => $exp];
        $rowsUpdated = $this->updateById($accountId, $bind);
        return $rowsUpdated;
    }
public function updateBalance($accountId, $delta)
    {
        if ($delta < 0) {
            $exp = '(`' . Entity::A_BALANCE . '`-' . abs($delta) . ')';
        } else {
            $exp = '(`' . Entity::A_BALANCE . '`+' . abs($delta) . ')';
        }
        $exp = new \Praxigento\Core\App\Repo\Query\Expression($exp);
        $bind = [Entity::A_BALANCE => $exp];
        $rowsUpdated = $this->updateById($accountId, $bind);
        return $rowsUpdated;
    }
Add/subtract value to/from account current balance.

@param int $accountId
@param float $delta change value (negative or positive)
@return int number of updated rows in DB