struct ConvCompany : Convert
{
        Value Format(const Value &q) const
        {
			SQL * Select(COM_NAME).From(COMPANY).Where(COM_ID == q);
			String company;
			if(SQL.Fetch())
				company = SQL[COM_NAME];
			else
				company = "";
			return q.IsNull() ? Null : company;
        }
};

.....
.....

projects.AddColumn(VPR_COMPANYID, t_("Customer")).SetConvert(Single<ConvCompany>());

projects.SetTable(PROJECTV),Leftjoined(COMPANY,VPR_COMPANYID),AS_PREFIX(VCOM_);
projects.AddColumn(VCOM_COMPANYNAME, t_("Customer"));