c# - 客户端评估 efcore 后无法处理集合操作

Question

Ef Core 接收错误

System.InvalidOperationException: Can't process set operations after client evaluation, consider moving the operation before the last Select() call (see issue #16243) at Microsoft.EntityFrameworkCore.Query.SqlExpressions.SelectExpression.ApplySetOperation(SetOperationType setOperationType, SelectExpression select2, Boolean distinct)

执行时

 public async Task<object> GetUnitsForDataTableAsync() =>
        
            await context.Units
             .Where(x => !x.TractUnitJunctions.Any())
              .Select(x => new
              {
                  x.Id,
                  x.UnitName,
                  x.UnitAcres,
                  TractNum = String.Empty,
                  Wells = String.Empty,
                  NumOfWells = 0,
              })
              .Union(
                        context.TractUnitJunctions
                        .Select(x => new
                         {
                            Id = x.UnitId,
                            x.Unit.UnitName,
                            x.Unit.UnitAcres,
                            x.Tract.TractNum,
                            Wells = string.Join(", ", x.TractUnitJunctionWellJunctions
                                              .Select(z => $"{z.Well.WellNum} ({z.Well.ApiNum})")
                                        ),
                            NumOfWells = x.TractUnitJunctionWellJunctions.Count()
                 }))
                .ToListAsync().ConfigureAwait(false);

但是，如果我将它分成两个查询，该函数可以正常工作。

 public async Task<object> GetUnitsForDataTableAsync()
        {
            var List1 = await context.Units
             .Where(x => !x.TractUnitJunctions.Any())
              .Select(x => new
              {
                  x.Id,
                  x.UnitName,
                  x.UnitAcres,
                  TractNum = String.Empty,
                  Wells = String.Empty,
                  NumOfWells = 0,
              })
             .ToListAsync().ConfigureAwait(false);

            var List2 = await context.TractUnitJunctions
                 .Select(x => new
                 {
                     Id = x.UnitId,
                     x.Unit.UnitName,
                     x.Unit.UnitAcres,
                     x.Tract.TractNum,
                     Wells = string.Join(", ", x.TractUnitJunctionWellJunctions
                                              .Select(z => $"{z.Well.WellNum} ({z.Well.ApiNum})")
                                        ),
                     NumOfWells = x.TractUnitJunctionWellJunctions.Count()
                 })
                .ToListAsync().ConfigureAwait(false);


            return List1.Concat(List2);
        }

我已经对该错误进行了一些研究，但我不确定如何重构第一个查询来解决该错误

Answer 1

在 .Union 之前为第一个查询添加 .AsEnumerable() 可以解决问题

如下

public async Task<object> GetUnitsForDataTableAsync() =>
    
        await context.Units
         .Where(x => !x.TractUnitJunctions.Any())
          .Select(x => new
          {
              x.Id,
              x.UnitName,
              x.UnitAcres,
              TractNum = String.Empty,
              Wells = String.Empty,
              NumOfWells = 0,
          }).AsEnumerable()
          .Union(
                    context.TractUnitJunctions
                    .Select(x => new
                     {
                        Id = x.UnitId,
                        x.Unit.UnitName,
                        x.Unit.UnitAcres,
                        x.Tract.TractNum,
                        Wells = string.Join(", ", x.TractUnitJunctionWellJunctions
                                          .Select(z => $"{z.Well.WellNum} ({z.Well.ApiNum})")
                                    ),
                        NumOfWells = x.TractUnitJunctionWellJunctions.Count()
             }))
            .ToListAsync().ConfigureAwait(false);