我尝试使用linqer，但是当我配置连接时它失败了，所以我自己写linq指令。最后我找到了答案。我没有提到实体之间的关系，但这在这里并不重要。

var summary = _context.FoundedAssets.Include(f => f.Manufacturer).
                Include(f => f.Asset).
                Include(f => f.PhisicalStockCheckSheet).ThenInclude(f => f.Inventory).
                Where(f => f.PhisicalStockCheckSheet.Inventory.ID == id).
                Select(x => new InventorySummaryModel()
                {
                    BarcodeNumber = x.BarcodeNumber.Value,
                    ManufacturerName = x.Manufacturer.Name,
                    Model = x.Model,
                    AssetsQuantity = x.Asset.Quantity,
                    FoundedAssetQuantity = x.Quantity
                }).ToList();

            var groupedSummary = summary.GroupBy(x => x.BarcodeNumber).Select(x => new InventorySummaryModel()
            {
                BarcodeNumber = x.First().BarcodeNumber,
                ManufacturerName = x.First().ManufacturerName,
                Model = x.First().Model,
                FoundedAssetQuantity = x.Sum(a => a.FoundedAssetQuantity),
                AssetsQuantity = x.First().AssetsQuantity
            }).ToList();

可能存在任何更简单的方法，但这一个工作正常。