避免 MongoDB 聚合中的空花括号
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【中文标题】避免 MongoDB 聚合中的空花括号【英文标题】：Avoiding Empty Curly Braces in MongoDB Aggregation 【发布时间】：2021-12-18 08:44:49 【问题描述】：我正在尝试通过 react chartjs 显示 mongodb 聚合结果。我的部分问题是我没有在后端实现正确的聚合输出。
当前聚合输出，其中包含不需要的空花括号
[
"_id":"Fubar",
"A_set":["A":"Y","A":"N",,],
"A_count_set":["A_count":1,"A_count":1,,],
"B_set":[,,"B":"N","B":"Y"],
"B_count_set":[,,"B_count":1,"B_count":1],
"_id":"Fubar2",
"A_set":["A":"Y","A":"N",,],
"A_count_set":["A_count":1,"A_count":1,,],
"B_set":[,,"B":"N","B":"Y"],
"B_count_set":[,,"B_count":1,"B_count":1]
]
我正在尝试实现缺少空花括号的 目标聚合输出
[
"_id":"Fubar",
"A_set":["A":"Y","A":"N"],
"A_count_set":["A_count":1,"A_count":1],
"B_set":["B":"N","B":"Y"],
"B_count_set":["B_count":1,"B_count":1],
"_id":"Fubar2",
"A_set":["A":"Y","A":"N"],
"A_count_set":["A_count":1,"A_count":1],
"B_set":["B":"N","B":"Y"],
"B_count_set":["B_count":1,"B_count":1]
]
管道操作
$facet:
A_branch: [
$group:
_id:
Q_id: "$A_id",
A_id: "$A_id"
,
A_count: $sum: 1
],
B_branch: [
$group:
_id:
Q_id: "$Q_id",
B_id: "$B_id"
,
B_count: $sum: 1
]
,
$project:
combined_group: $setUnion: ['$A_branch','$B_branch']
,
$unwind: '$combined_group',
$lookup:
from: "Q",
localField: "combined_group._id.Q_id",
foreignField: "_id",
as: "QRef"
,
$unwind: "$QRef" ,
$lookup:
from: "A",
localField: "combined_group._id.A_id",
foreignField: "_id",
as: "ARef"
,
$unwind: path:"$ARef", preserveNullAndEmptyArrays: true ,
$lookup:
from: "B",
localField: "combined_group._id.B_id",
foreignField: "_id",
as: "BRef"
,
$unwind: path:"$BRef", preserveNullAndEmptyArrays: true ,
$group:
_id: "$QRef.text",
A_set:
$push:
A: "$ARef.value"
,
A_count_set:
$push:
A_count: "$combined_group.A_count"
,
B_set:
$push:
B: "$BRef.value"
,
B_count_set:
$push:
B_count: "$combined_group.B_count"
聚合输入
"_id" : ObjectId("618..."),
"Q_id" : ObjectId("618..."),
"B_id" : ObjectId("618..."),
"A_id" : ObjectId("618...")
"_id" : ObjectId("618..."),
"Q_id" : ObjectId("618..."),
"B_id" : ObjectId("618..."),
"A_id" : ObjectId("618...")
"_id" : ObjectId("618..."),
"Q_id" : ObjectId("618..."),
"B_id" : ObjectId("618..."),
"A_id" : ObjectId("618...")
"_id" : ObjectId("618..."),
"Q_id" : ObjectId("618..."),
"B_id" : ObjectId("618..."),
"A_id" : ObjectId("618...")
【问题讨论】：
【参考方案1】：在管道末尾使用$filter
db.collection.aggregate([
"$set":
"A_set":
"$filter":
"input": "$A_set",
"as": "x",
"cond": "$ne": [ "$$x", ]
,
"$set":
"A_count_set":
"$filter":
"input": "$A_count_set",
"as": "x",
"cond": "$ne": [ "$$x", ]
,
"$set":
"B_set":
"$filter":
"input": "$B_set",
"as": "x",
"cond": "$ne": [ "$$x", ]
,
"$set":
"B_count_set":
"$filter":
"input": "$B_count_set",
"as": "x",
"cond": "$ne": [ "$$x", ]
])
mongoplayground
【讨论】：
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