我的查询表达式在执行时工作正常。

var topQuery1 = (
    from rov in context.Rocks
        .Where(x => eIds.Contains(x.RockId))

    join ro in context.Rocks
        .Where(x => x.Break == "OUT")
        .OrderByDescending(x => x.Timestamp)
        on
           new { rov.WorkerId, rov.Flatter } equals
           new { ro.WorkerId, ro.Flatter }
           into _rovOut

    from rovOut in _rovOut.DefaultIfEmpty()

    join ao in context.Workers()
        on rov.WorkerId equals ao.WorkerId
           into _profile

    from profile in _profile.DefaultIfEmpty()

    select new { rov, rovOut, profile }
);

字符串
我把上面的代码翻译成这个fluentAPI，并没有像预期的那样工作。

var topQuery2 = context.Rocks.Where(x => eIds.Contains(x.RockId))
.GroupJoin(context.Workers(),
    r => r.WorkerId,
    p => p.WorkerId,
    (a, b) => new { profile = b.SingleOrDefault(), rov = a })
.GroupJoin(context.Rocks.Where(x => x.Break == "OUT").OrderByDescending(x => x.Timestamp),
    a => new { a.rov.WorkerId, a.rov.Flatter },
    b => new { b.WorkerId, b.Flatter },
    (a, b) => new { rovOut = b.SingleOrDefault(), rov = a.rov, profile = a.profile });

型
它会产生错误：
创建查询字符串时出错：LINQ表达式'DbSet（）。其中（x => __eIds_0 .Contains（x.RockId））.GroupJoin（inner：DbSet（），outerKeySet：r => r.WorkerId，innerKeySet：p => p.WorkerId，resultValue：无法翻译（a，B）=> new { profile = B.SingleOrDefault（），rov = a }）“。请以可翻译的形式重写查询，或通过插入对“AsEnumerable”、“AsAsAsyncEnumerable”、“ToList”或“ToListAsync”的调用来显式切换到客户端计算。有关详细信息，请参阅https://go.microsoft.com/fwlink/?linkid=2101038。
[编辑]**
我最终从这个URL https://velog.io/@prediction/EF-CORE-Left-Join-Extension使用LeftJoin，现在一切都正常。