使用外连接的 Linq 查询没有 return 预期结果

Question

这可能很简单，但我就是做不对。这是我的接线 - 事件与规则有多对多关系。事件可能有也可能没有规则。规则将有自己的详细信息。总之，我需要这样的对象：

object
- event
- rule (null)
- list of mappings (null)

所以，我将这些关系硬编码如下

Dim eventList As new List(Of [Event])
eventList.Add(new [Event]() With {.EventId = 1, .ClassId = 1, .TypeId = 1, .EventSequence = 2}) ' this is event without rules
eventList.Add(new [Event]() With {.EventId = 2, .ClassId = 1, .TypeId = 1, .EventSequence = 1})
eventList.Add(new [Event]() With {.EventId = 3, .ClassId = 1, .TypeId = 1, .EventSequence = 3})


Dim ruleEventList As New List(Of RuleEvent)
ruleEventList.Add(new RuleEvent() With {.Id = 1, .EventId = 2, .RuleId = 1})
ruleEventList.Add(new RuleEvent() With {.Id = 2, .EventId = 3, .RuleId = 1})


Dim ruleList As New List(Of Rule)
ruleList.Add(new Rule() With {.Id = 1, .EntityId = 1, .SearchId = 1})


Dim ruleDetailList As New List(Of RuleDetail)
ruleDetailList.Add(new RuleDetail() With {.Id = 1, .RuleId = 1, .Value = "aaa"})
ruleDetailList.Add(new RuleDetail() With {.Id = 2, .RuleId = 1, .Value = "bbb"})

这似乎是正确的，因为 2/3 工作正常。但这里是 LINQ

Dim eventRuleDetailList = _
    From ev In eventList
    From re In ruleEventList.Where(Function(r) r.EventId = ev.EventId).DefaultIfEmpty()
    From rule In ruleList.Where(Function(r) re IsNot Nothing AndAlso r.Id = re.RuleId).DefaultIfEmpty()
    From det In ruleDetailList.Where(Function(r) rule IsNot Nothing AndAlso r.RuleId = rule.Id).DefaultIfEmpty()
    Group ev, rule, det By ev.EventId, ev.ClassId, ev.TypeId, ev.EventSequence
        Into g = Group
    Order By ClassId, TypeId, EventSequence
    Select New With
        {
            .EventId = EventId,
            .Event = g.First().ev,
            .Rule = g.First().rule,
            .Details = g.Select(Function(itm) itm.det) '<-- This is my glitch 
        }

结果似乎几乎正确，但有一个问题。我好像听不懂"Details"

For Each erd In eventRuleDetailList
    Console.WriteLine("Event Id: {0}; Event Seq: {1}; Rule Id: {2}; Details: {3}", 
        erd.EventId, 
        erd.Event.EventSequence, 
        If (erd.Rule Is Nothing,  "No Rules", erd.Rule.Id),
        If (erd.Details Is Nothing,  "No Details",  "Yes Details")
    )

Next

输出：

Event Id: 2; Event Seq: 1; Rule Id: 1; Details: Yes Details
Event Id: 1; Event Seq: 2; Rule Id: No Rules; Details: Yes Details
Event Id: 3; Event Seq: 3; Rule Id: 1; Mapped Details: Yes Details

问题来了。我做错了，因为 Event Id: 1 应该说 "No Details"。它有 "No Rules"

谢谢

Answer 1

以与规则相同的方式指示详细信息：

            .Rule = g.First().rule,
            .Details = g.First().det,

Answer 2

我成功了

这是 Select 需要稍微调整的部分

Select New With
    {
        .EventId = EventId,
        .Event = g.First().ev,
        .Rule = g.First().rule,
        .Details = if(g.First().rule is nothing, nothing, g.Select(Function(itm) itm.det)) 
    }

输出为

Event Id: 2; Event Seq: 1; Rule Id: 1; Details: Yes Details
Event Id: 1; Event Seq: 2; Rule Id: No Rules; Details: No Details
Event Id: 3; Event Seq: 3; Rule Id: 1; Mapped Details: Yes Details

使用外连接的 Linq 查询没有 return 预期结果

Linq query with outer join doesn't return expected result

linq

vb.net

linq-to-objects