public class StringTools
{
    
    /// <summary>
    /// Первый символ заглавной буквы
    /// </summary>
    /// <param name="value"></param>
    /// <returns></returns>
    public static string ToFirstUpperPinYin(string value)
    {
        if (!string.IsNullOrEmpty(value))
            return PinyinHelper.GetInitial(value).ToUpper();
        return value;
    }
}

var methodInfo = typeof(StringTools).GetMethod("ToFirstUpperPinYin");
var query = _db.Queryable<GoodsInventory, Goods, Manufacturer, GoodsPrice>(
                (a, b, c, d) => new JoinQueryInfos(
                    JoinType.Left, a.GoodsId == b.Id,
                    JoinType.Left, c.Id == b.ManufacturerId,
                    JoinType.Left, d.GoodsId == b.Id
                ))
               .Select((a, b, c, d) => new GoodsInventoryOut()
               {
                   GoodsInventoryId = a.Id,
                   GoodsCode = b.Code,
                   GoodsName = b.Name,
                   GoodsHelperCode = SqlFunc.OnlyInSelectConvertToString(b.Name, methodInfo),
                   //Пропустить остальное
               }, true)
               .MergeTable();