Question

我找不到为什么此IQueryable无法正常工作的原因，我尝试了一些不同的方法，但总是回退到同一错误，'InMemoryProjectionBindingExpressionVisitor'失败。这可能表示EF Core中存在错误或局限性

：

var q = _QueryService.GetSomeInformation(db, cp.Attributes, min, max);

        var query = q
            .Join(db.SomeTable
                    .Where(mc => mc.Attribute.Total >= minimumValue),
                s => s.Code,
                c => c.Code,
                (s, c) => new {s, c})
            //.AsEnumerable()
            .GroupBy(@t => new {@t.c.Year, @t.c.Month}, @t => @t.c)
            .Select(cg => new
            {

                cg.Key.Year,
                cg.Key.Month,
                P1 = cg.Average(i => i.Attribute.P1),
                P2 = cg.Average(i => i.Attribute.P2),
                P3 = cg.Average(i => i.Attribute.P3),
                P4 = cg.Average(i => i.Attribute.P4),
                P5 = cg.Average(i => i.Attribute.P5),
                P6 = cg.Average(i => i.Attribute.P6),
                Total = cg.Average(i => i.Attribute.Total),
                N = cg.Count(),
                NumberOfPeriods = 1

            })
            .OrderBy(@t => @t.Year)
            .ThenBy(@t => @t.Month);

如果我取消注释'.AsEnumerable（）'，它可以像在客户端执行的那样完美运行，但是如果没有在服务器端执行GroupBy，则联接的行数可能会太高，有时我会得到OutOfMemmory错误或超时错误。

有人知道如何将此查询转换为Entity Framework Core 3.1.5上的有效查询吗？预先感谢！

Answer 1

感谢@IvanStoev的提示，该错误已通过在GroupBy上显式投影所需的字段而消失：

var q = _QueryService.GetSomeInformation(db, cp.Attributes, min, max);

    var query = q
        .Join(db.SomeTable
                .Where(mc => mc.Attribute.Total >= minimumValue),
            s => s.Code,
            c => c.Code,
            (s, c) => new {s, c})
        .GroupBy(@t => new {@t.c.Year, @t.c.Month}, @t => @t.c.Attribute)
        .Select(cg => new
        {

            cg.Key.Year,
            cg.Key.Month,
            P1 = cg.Average(i => i.P1),
            P2 = cg.Average(i => i.P2),
            P3 = cg.Average(i => i.P3),
            P4 = cg.Average(i => i.P4),
            P5 = cg.Average(i => i.P5),
            P6 = cg.Average(i => i.P6),
            Total = cg.Average(i => i.Total),
            N = cg.Count(),
            NumberOfPeriods = 1

        })
        .OrderBy(@t => @t.Year)
        .ThenBy(@t => @t.Month);

EF核心“ InMemoryProjectionBindingExpressionVisitor”失败。这可能表示EF Core

1 个答案: