Question

我有一个linq查询，我需要根据testTypeId，testTakerId，subAreaId，subjectName，testDate.Value.Month，testDate.Value.Year在一个月内选择最高测试日期进行分组。

我遇到的问题是嵌套列表的关注点。有没有办法将数据展平为testTakerId，testTypeId，subAreaId，subjectName，testDate.Value.Month，testDate.Value.Year。

非嵌套值（testTakerId，test.Value.Month等）工作正常，但是嵌套（subAreaId）值我遇到了麻烦。

        var q1 = from entry in result
                 let testDate = entry.result.TestDate
                 where testDate != null
                 group entry by new { entry.testTakerId, entry.testInstance.Select(
                sr => sr.Subject.Select(c => c.subArea.Id)), entry.testInstance.Select(
                sr => sr.Subject.Select(c => c.subArea.Name)),entry.testInstance.Select(
                sr => sr.testInstance.Test.TestType.Id), testDate.Value.Month, 
                   testDate.Value.Year } into g
                 select g.Where(entry => entry.result.TestDate == g.Max(e => e.result.TestDate));

Answer 1

您必须首先通过加入包含的集合（testInstance和Subject）来展平结果集，然后进行分组：

var q1 = from entry in result
        from ti in entry.testInstance  // translates to a SQL join
        from su in ti.Subject          // translates to a SQL join
        let testDate = entry.result.TestDate
        where testDate != null
        group entry by new 
        {
            entry.testTakerId,
            su.subArea.Id,
            su.subArea.Name,
            ti.Test.TestType.Id,
            testDate.Value.Month, 
            testDate.Value.Year
        } 
        into g
        select g.Where(entry => entry.result.TestDate == 
                                    g.Max(e => e.result.TestDate));

在流利（或方法）语法中，from ti in entry.testInstance之类的语句等同于SelectMany。

在linq中展平数据

1 个答案: