MongoDb.Linq 条件聚合器的等效查询

Question

我按以下方式将我的数据与 MongoDb.Linq 分组：

group r1 by new { r1.SupId, r1.SupFullName } into g2
select new
{
    g2.Key.SupFullName,
    Volunteers = from v0 in g2
                 where v0.VolId != g2.Key.SupId
                 select new { v0.VolFullName, v0.VolPeopleCount }
}

也就是说，我只想要 Volunteers 中 Id 与组密钥不同的那些。我期待驱动程序生成条件 $push，但它给出了一个简单的条件：

"$push" : { 
    "VolFullName" : "$VolFullName", 
    "VolPeopleCount" : "$VolPeopleCount" 
}

现在，通过阅读本文，我能够将上述查询转换为以下查询：

"$push": {
    "$cond": [
        { "$ne": [ "$VolId", "$SupId" ] },
        { 
            "VolFullName": "$VolFullName",
            "VolPeopleCount": "$VolPeopleCount"
        },
        null
     ]
 }

这给了我想要的结果。我想知道如何（如果可能的话）指示 csharp 驱动程序生成如上所述的查询。提前致谢！

编辑： 按照@mickl 的建议，我能够生成一个条件 $push（以及一个条件 $sum），但结果并不像预期的。假设我的 collection:

中有以下文档

{ N: "P_1", S: { I: "S_1", FN: "S_1" }, C: { I: "S_1", FN: "S_1" } }
{ N: "P_2", S: { I: "S_1", FN: "S_1" }, C: { I: "S_1", FN: "S_1" } }
{ N: "P_3", S: { I: "S_1", FN: "S_1" }, C: { I: "S_1", FN: "S_1" } }
{ N: "P_4", S: { I: "S_1", FN: "S_1" }, C: { I: "C_2", FN: "C_2" } }
{ N: "P_5", S: { I: "S_1", FN: "S_1" }, C: { I: "C_2", FN: "C_2" } }
{ N: "P_6", S: { I: "S_1", FN: "S_1" }, C: { I: "C_2", FN: "C_2" } }
{ N: "P_7", S: { I: "S_1", FN: "S_1" }, C: { I: "C_3", FN: "C_3" } }
{ N: "P_8", S: { I: "S_1", FN: "S_1" }, C: { I: "C_3", FN: "C_3" } }
{ N: "P_9", S: { I: "S_1", FN: "S_1" }, C: { I: "C_3", FN: "C_3" } }

这里的N、I、FN、S和C分别表示姓名、id、全名、主管和创建者。因此，正如您所看到的，主管 S_1 正在监督每个文档，已经创建了 3 个文档，并且有 6 个文档由 2 个其他创建者创建，他们也受到 S_1 的监督。我想做的是由主管总结这些文档，然后由创建者总结文档（人）的数量。所以，我的 LINQ 查询看起来像：

var q = from p in col.AsQueryable()
        group p by new
        {
           SupFullName = p.S.FN,
           SupId = p.S.I,
           CtorFullName = p.C.FN,
           CtorId = p.C.I
        } into g1
        select new
        {
            g1.Key.SupFullName,
            g1.Key.SupId,
            VolFullName = g1.Key.CtorFullName,
            VolId = g1.Key.CtorId,
            VolPeopleCount = g1.LongCount()
        } into r1
        group r1 by new { r1.SupId, r1.SupFullName } into g2
        select new
        {
           g2.Key.SupFullName,
           g2.Key.SupId,
           Volunteers = g2.Select(v => v.VolId != g2.Key.SupId
                           ? new { v.VolId, v.VolFullName, v.VolPeopleCount }
                           : null),
          SupPeopleCount = g2.Select(v => v.VolId == g2.Key.SupId 
                               ? v.VolPeopleCount 
                               : 0).Sum()
        } into r2
        orderby r2.SupPeopleCount descending
        select r2;

查询给我的输出是：

Supervisor: S_1, PeopleCount: 0
   Creator: C_3, PeopleCount: 3
   Creator: C_2, PeopleCount: 3
   Creator: S_1, PeopleCount: 3

这不是我想要的。正确的输出是

Supervisor: S_1, PeopleCount: 3
   Creator: C_3, PeopleCount: 3
   Creator: C_2, PeopleCount: 3

它按以下方式生成条件聚合器（如果我删除条件中的前缀 $_id 并只留下 $SupId 它就像一个魅力）：

"__agg0": {
      "$push": {
         "$cond": [
             { "$ne": [ "$VolId", "$_id.SupId" ] },
             {
                "VolId": "$VolId",
                "VolFullName": "$VolFullName",
                "VolPeopleCount": "$VolPeopleCount"
             },
             null
         ]
      }
},
"__agg1": {
    "$sum": {
       "$cond": [
           { "$eq": [ "$VolId", "$_id.SupId" ] },
           "$VolPeopleCount",
           NumberLong(0)
       ]
   }
}

谢谢！

Answer 1

您可以运行 Select 并在 LINQ 语句中使用三元运算符：

group r1 by new { r1.SupId, r1.SupFullName } into g2
select new
{
    g2.Key.SupFullName,
    Volunteers = g2.Select(x => x.VolId != x.SupId ? new { x.VolFullName, x.VolPeopleCount }: null)  
};

这被翻译成以下聚合管道：

{ 
    "$group" : { 
        "_id" : { "SupId" : "$SupId", "SupFullName" : "$SupFullName" }, 
        "__agg0" : { 
            "$push" : { 
                "$cond" : [
                        { "$ne" : ["$VolId", "$SupId"] }, 
                        { "VolFullName" : "$VolFullName", "VolPeopleCount" : "$VolPeopleCount" }, 
                        null
                    ] 
                } 
            } 
        } 
}, 
{ "$project" : { "SupFullName" : "$_id.SupFullName", "Volunteers" : "$__agg0", "_id" : 0 } }

MongoDb.Linq 条件聚合器的等效查询

MongoDb.Linq equivalent query for conditional aggregator

c#

linq

mongodb

aggregation-framework

mongodb-.net-driver