如何在EF中实现left join（左联接）查询

var list = from a in context.Set<Table1>()
                               join b in context.Set<Table2>()
                               on a.Id equals b.Id into ab
                               from abi in ab.DefaultIfEmpty()
                               join c in context.Set<Table3>()
                               on a.SubId equals c.Id into ac
                               from aci in ac.DefaultIfEmpty()
                               where a.IsValid
                               select new OutXXXDto()
                               {
                                   Barcode = abi.Barcode,
                                   CustomerName = abi.CustomerName,
                                   HandlingTime = a.HandlingTime.ToString("yyyy-MM-dd hh:mm:ss"),
                                   Products = aci == null ? string.Empty : string.Join(",", aci.Sublist.Where(p => p.IsValid && p.Id.Equals(aci.Id)).Select(p => p.ProductName)),
                                   SubBarcode = aci == null ? string.Empty : aci.Barcode,
                               };