C#groupby使用AsQueryable的报错

问题描述

var commodity = _appDbContext.ArchivesCcommodity.Where(lambda)
          .GroupJoin(_appDbContext.ArchivesCcommoditySpecification,a => a.Code,b => b.commodity,(a,b) => new { a,b })
          .SelectMany(a => a.b.DefaultIfEmpty(),b) => new { a.a,b })
          .GroupJoin(_appDbContext.ArchivesCSpecificationDetail,a => a.a.a.b.SpecificationDetail,d => d.Code,d) => new { a,d })
          .SelectMany(a => a.d.DefaultIfEmpty(),d) => new
          {
              commodity = a.a.a.Code,commodityName = a.a.a.Name,SpecificationDetailName = d.Name,OrderSN = d.OrderSN
          }).AsQueryable().OrderBy(a => a.OrderSN).GroupBy(a => new { a.commodity,a.commodityName })
           .Select(a => new
           {
               commodity = a.Key.commodity,commodityName = a.Key.commodityName,SpecificationDetailName = string.Join(" - ",a.Select(a => a.SpecificationDetailName)),SpecificationDetailTotal = string.Join(" - ",a.Select(a => a.SpecificationDetailName)) == "" ? 0 : a.Count()
           });

其中 .AsQueryable() 会导致错误

.AsQueryable()
.OrderBy(a => a.OrderSN)
.GroupBy(a => new { a.commodity,a.commodityName })

改成AsEnumerable()不会报错

.ASEnumerable()
.OrderBy(a => a.OrderSN)
.GroupBy(a => new { a.commodity,a.commodityName })

但是我暂时不想把这段代码发送到数据库中，因为它会在分页查询后发送。不知道怎么处理？

////////////我把我的完整代码贴出来，说说我的实际需求

查询代码，逐页查询数据库。例如，只检查一页和 10 行记录。这里没问题。

            var AA= _appDbContext.ArchivesCcommodity.Where(lambda)
              .GroupJoin(_appDbContext.ArchivesCcommoditySpecification,b })
              .SelectMany(a => a.b.DefaultIfEmpty(),b })
              .GroupJoin(_appDbContext.ArchivesCSpecificationDetail,a => a.a.b.SpecificationDetail,d })
              .SelectMany(a => a.d.DefaultIfEmpty(),d) => new
              {
                  commodity = a.a.a.a.a.Code,commodityName = a.a.a.a.a.Name,OrderSN = d.OrderSN
              });

            PageHealper<object> page = new PageHealper<object>();

            page.Start(pageNum,pageSize);

            page = await page.RestPage(AA);

这时候又分组整理了一下，现在发现：

不是操作分页查询结果，而是查询所有AA数据库。
根据之前的分页查询，得到行数和页码。这里，通过分组和合并来改变行数。这就是为什么我想把分组和排序放在一起，最后是分页。

  var BB = AA.AsEnumerable().OrderBy(a => a.OrderSN).GroupBy(a => new { a.commodity,a.commodityName,a.Specification,a.SpecificationName })
               .Select(a => new
               {
                   commodity = a.Key.commodity,a.Select(a => a.SpecificationDetailName)) == "" ? 0 : a.Count()
               }); ;

            page.Data = BB.ToList<object>();
            return page;

解决方法

查看这篇文章https://weblogs.asp.net/zeeshanhirani/using-asqueryable-with-linq-to-objects-and-linq-to-sql，了解 AsQueryable 的作用。

我认为你真的不需要 AsQueryable ...... LINQ to SQL 不喜欢该查询的某些内容。

它不喜欢 String.Join(...) 因为它无法翻译它。

所以你可以做的一件事是将 .AsEnumerable() 放在 GroupBy() 之后，这将在 SQL 中执行所有操作，然后在内存中执行所有操作。

例如：

var commodity = _appDbContext.ArchivesCCommodity.Where(lambda)
        .GroupJoin(_appDbContext.ArchivesCCommoditySpecification,a => a.Code,b => b.Commodity,(a,b) => new { a,b })
        .SelectMany(a => a.b.DefaultIfEmpty(),b) => new { a.a,b })
        .GroupJoin(_appDbContext.ArchivesCSpecificationDetail,a => a.a.a.b.SpecificationDetail,d => d.Code,d) => new { a,d })
        .SelectMany(a => a.d.DefaultIfEmpty(),d) => new
        {
            Commodity = a.a.a.Code,CommodityName = a.a.a.Name,SpecificationDetailName = d.Name,OrderSN = d.OrderSN
        }).OrderBy(a => a.OrderSN).GroupBy(a => new { a.Commodity,a.CommodityName })
        .AnEnumerable()
        .Select(a => new
        {
            Commodity = a.Key.Commodity,CommodityName = a.Key.CommodityName,SpecificationDetailName = string.Join(" - ",a.Select(a => a.SpecificationDetailName)),SpecificationDetailTotal = string.Join(" - ",a.Select(a => a.SpecificationDetailName)) == "" ? 0 : a.Count()
        });

asqueryable c#c#