MongoDB聚合$elemMatch内$lookup阶段

我有一个MongoDB系列，看起来像这样：

{
    players: [
        {uuid: "A"},
        {uuid: "B"}
    ]
},
{
    players: [
        {uuid: "A"},
        {uuid: "C"}
    ]
},
{
    players: [
        {uuid: "D"},
        {uuid: "E"}
    ]
}

{ 
    "playerId" : "A"
}
{ 
    "playerId" : "B"
}
{ 
    "playerId" : "C"
}

我想使用上一个聚合阶段的结果，现在使用

$lookup

阶段查找播放器显示的所有文档：

from: "collection",
pipeline: [
    {
        $match: {
            players: {
                $elemMatch: {
                    uuid: "$playerId" 
                }
            }
            //using "players.uuid": "$playerId" doesn't work either
        }
    }
],
as: "field"

my

$lookup

阶段的输入如下所示：

{
    players: [
        {uuid: "A"},
        {uuid: "B"}
    ]
},
{
    players: [
        {uuid: "A"},
        {uuid: "C"}
    ]
},
{
    players: [
        {uuid: "D"},
        {uuid: "E"}
    ]
}

{ 
    "playerId" : "A"
}
{ 
    "playerId" : "B"
}
{ 
    "playerId" : "C"
}

此查询在

字段中返回一个空数组。似乎
$uuid
的计算结果不正确，因为如果我用硬编码值（例如
a
）交换
$uuid
，此查询将返回结果

我也尝试过使用
let
属性，这给了我同样的结果。
我做错了什么？
使用您提供的文档。我相信这可能对你有用：

我使用了
$lookup
对包含
playerId
的集合进行联接，该集合创建了一个名为
字段的
数组。然后我使用
$unwind
从
字段
和
播放器
中提取所有数组元素。最后，我使用
$cond
交叉检查两个值是否匹配

db.getCollection('foo').aggregate([
{ $lookup : {
    from: "bar",
    localField: "players.uuid",
    foreignField: "playerId",
    as: "field"
    } },
    { $unwind : "$players" },
    { $unwind : "$field" },
    { $project : { 
      "players": 1, 
      "field" : 1, 
      "isMatch": { 
      "$cond": [ { "$eq": ["$players.uuid", "$field.playerId"] }, 1, 0 ] 
      } } }
    ])

我故意让输出冗长

/* 1 */
{
    "_id" : ObjectId("5a7f534b337e8d2b97ff2ffb"),
    "players" : {
        "uuid" : "A"
    },
    "field" : {
        "_id" : ObjectId("5a7f5374337e8d2b97ff2ffe"),
        "playerId" : "A"
    },
    "isMatch" : 1.0
}

/* 2 */
{
    "_id" : ObjectId("5a7f534b337e8d2b97ff2ffb"),
    "players" : {
        "uuid" : "A"
    },
    "field" : {
        "_id" : ObjectId("5a7f539b337e8d2b97ff2fff"),
        "playerId" : "B"
    },
    "isMatch" : 0.0
}

/* 3 */
{
    "_id" : ObjectId("5a7f534b337e8d2b97ff2ffb"),
    "players" : {
        "uuid" : "B"
    },
    "field" : {
        "_id" : ObjectId("5a7f5374337e8d2b97ff2ffe"),
        "playerId" : "A"
    },
    "isMatch" : 0.0
}

/* 4 */
{
    "_id" : ObjectId("5a7f534b337e8d2b97ff2ffb"),
    "players" : {
        "uuid" : "B"
    },
    "field" : {
        "_id" : ObjectId("5a7f539b337e8d2b97ff2fff"),
        "playerId" : "B"
    },
    "isMatch" : 1.0
}

/* 5 */
{
    "_id" : ObjectId("5a7f5356337e8d2b97ff2ffc"),
    "players" : {
        "uuid" : "A"
    },
    "field" : {
        "_id" : ObjectId("5a7f5374337e8d2b97ff2ffe"),
        "playerId" : "A"
    },
    "isMatch" : 1.0
}

/* 6 */
{
    "_id" : ObjectId("5a7f5356337e8d2b97ff2ffc"),
    "players" : {
        "uuid" : "A"
    },
    "field" : {
        "_id" : ObjectId("5a7f53a8337e8d2b97ff3000"),
        "playerId" : "C"
    },
    "isMatch" : 0.0
}

/* 7 */
{
    "_id" : ObjectId("5a7f5356337e8d2b97ff2ffc"),
    "players" : {
        "uuid" : "C"
    },
    "field" : {
        "_id" : ObjectId("5a7f5374337e8d2b97ff2ffe"),
        "playerId" : "A"
    },
    "isMatch" : 0.0
}

/* 8 */
{
    "_id" : ObjectId("5a7f5356337e8d2b97ff2ffc"),
    "players" : {
        "uuid" : "C"
    },
    "field" : {
        "_id" : ObjectId("5a7f53a8337e8d2b97ff3000"),
        "playerId" : "C"
    },
    "isMatch" : 1.0
}

你能用样本文档从集合发帖吗？我的帖子的顶部包含样本文档。这是我想加入的字段名，但似乎不起作用。@Joba你能用这个集合的示例更新你的OP吗。然后我可以设置一个测试，看看我是否能提供帮助。目前我只有你一半的问题：-）更新了OP并澄清了我的示例，但为什么按主题开始的初始请求不起作用？