我有一个看起来像这样的 MongoDB 集合:
{
players: [
{uuid: "A"},
{uuid: "B"}
]
},
{
players: [
{uuid: "A"},
{uuid: "C"}
]
},
{
players: [
{uuid: "D"},
{uuid: "E"}
]
}
我想使用前一个聚合阶段的结果,现在使用
$lookup
查找玩家出现的所有文档。阶段:from: "collection",
pipeline: [
{
$match: {
players: {
$elemMatch: {
uuid: "$playerId"
}
}
//using "players.uuid": "$playerId" doesn't work either
}
}
],
as: "field"
我的
$lookup
的输入舞台看起来像这样:{
"playerId" : "A"
}
{
"playerId" : "B"
}
{
"playerId" : "C"
}
此查询在
field
中返回一个空数组.好像$uuid
没有得到正确评估,因为如果我交换 $uuid
使用硬编码值(例如 A
),此查询返回结果。我也试过使用
let
属性(property),这给了我同样的结果。我究竟做错了什么?
最佳答案
使用您提供的文件。我相信这可能对你有用:
我用过 $lookup
加入包含 playerId
的集合,这会创建一个 array
叫 field
.然后我使用 $unwind
从 field
中提取所有数组元素和 player
.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", "$field.playerId"] }, 1, 0 ]
} } }
])
我故意让输出详细..
/* 1 */
{
"_id" : ObjectId("5a7f534b337e8d2b97ff2ffb"),
"players" : {
"uuid" : "A"
},
"field" : {
"_id" : ObjectId("5a7f5374337e8d2b97ff2ffe"),
"playerId" : "A"
},
"isMatch" : 1.0
}
/* 2 */
{
"_id" : ObjectId("5a7f534b337e8d2b97ff2ffb"),
"players" : {
"uuid" : "A"
},
"field" : {
"_id" : ObjectId("5a7f539b337e8d2b97ff2fff"),
"playerId" : "B"
},
"isMatch" : 0.0
}
/* 3 */
{
"_id" : ObjectId("5a7f534b337e8d2b97ff2ffb"),
"players" : {
"uuid" : "B"
},
"field" : {
"_id" : ObjectId("5a7f5374337e8d2b97ff2ffe"),
"playerId" : "A"
},
"isMatch" : 0.0
}
/* 4 */
{
"_id" : ObjectId("5a7f534b337e8d2b97ff2ffb"),
"players" : {
"uuid" : "B"
},
"field" : {
"_id" : ObjectId("5a7f539b337e8d2b97ff2fff"),
"playerId" : "B"
},
"isMatch" : 1.0
}
/* 5 */
{
"_id" : ObjectId("5a7f5356337e8d2b97ff2ffc"),
"players" : {
"uuid" : "A"
},
"field" : {
"_id" : ObjectId("5a7f5374337e8d2b97ff2ffe"),
"playerId" : "A"
},
"isMatch" : 1.0
}
/* 6 */
{
"_id" : ObjectId("5a7f5356337e8d2b97ff2ffc"),
"players" : {
"uuid" : "A"
},
"field" : {
"_id" : ObjectId("5a7f53a8337e8d2b97ff3000"),
"playerId" : "C"
},
"isMatch" : 0.0
}
/* 7 */
{
"_id" : ObjectId("5a7f5356337e8d2b97ff2ffc"),
"players" : {
"uuid" : "C"
},
"field" : {
"_id" : ObjectId("5a7f5374337e8d2b97ff2ffe"),
"playerId" : "A"
},
"isMatch" : 0.0
}
/* 8 */
{
"_id" : ObjectId("5a7f5356337e8d2b97ff2ffc"),
"players" : {
"uuid" : "C"
},
"field" : {
"_id" : ObjectId("5a7f53a8337e8d2b97ff3000"),
"playerId" : "C"
},
"isMatch" : 1.0
}
关于$lookup 阶段内的 MongoDB 聚合 $elemMatch,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/48721925/