[英]Mongo DB query to return count?
我有兩個集合Course
和File
。 這是我從Course
集合中獲得的數據
[{
_id: 1,
name: "Course1",
price: "100"
},
{
_id: 2,
name: "Course2",
price: "200"
}]
這是我的文件收集數據
[{
_id: 1,
name: "File1",
isFree: true,
courseId: 1
}
{
_id: 2,
name: "File2",
isFree: false,
courseId: 1
}
{
_id: 3,
name: "File3",
isFree: false,
courseId: 1
}]
我想用Course name
、 Count of files which are free
Count of files which are not free
Count of files which are free
檢索課程 1。
我的嘗試:
Course.aggregate([
{$lookup:{
from:"files",
localField: "_id",
foreignField: "courseId",
as: "files"
}},
])
如果我執行上述查詢,這是我的回應:
[
{
"_id": "6161bdcc0aada09d81598840",
"name": "Course1",
"files": [
{
"_id": "6166a0814ad3f56b71232b9c",
"name": "File1.jpeg",
"isFree":true
},
{
"_id": "6166a0814ad3f56b71232b9d",
"name": "File2.jpeg",
"isFree":false
},
{
"_id": "6166a0814ad3f56b71232b9v",
"name": "File3.jpeg",
"isFree":false
}
]
}
]
我希望我的輸出為:
[
{
"_id": "6161bdcc0aada09d81598840",
"name": "Course1",
"files": {"free": 1,"paid": 2}
}
]
您可以嘗試使用管道查找,
$lookup
與管道,在let
傳遞courseId
$match
courseId
條件$group
by isFeee
並獲得總數$project
以 k(key) 和 v(value) 格式顯示必填字段$cond
檢查isFree
是否isFree
真,然后返回“free”,否則返回“paid”$addFields
更新files
數組$arrayToObject
將files
鍵值數組轉換為對象$ifNull
檢查屬性是否不存在然后設置 0await Course.aggregate([
{
$lookup: {
from: "files",
let: { courseId: "$_id" },
pipeline: [
{ $match: { $expr: { $eq: ["$$courseId", "$courseId"] } } },
{
$group: {
_id: "$isFree",
count: { $sum: 1 }
}
},
{
$project: {
_id: 0,
k: { $cond: ["$_id", "free", "paid"] },
v: "$count"
}
}
],
as: "files"
}
},
{
$addFields: {
files: { $arrayToObject: "$files" }
}
},
{
$addFields: {
"files.free": { $ifNull: ["$files.free", 0] },
"files.paid": { $ifNull: ["$files.paid", 0] }
}
}
])
嘗試以下操作:
db.course.aggregate([
{
$lookup: {
from: "files",
localField: "_id",
foreignField: "courseId",
as: "files",
},
},
{
$unwind: {
path: "$files",
preserveNullAndEmptyArrays: true,
},
},
{
$group: {
_id: "$_id",
name: {
$first: "$name",
},
price: {
$first: "$price",
},
free: {
$sum: {
$cond: [
{
$eq: ["$files.isFree", true],
},
1,
0,
],
},
},
paid: {
$sum: {
$cond: [
{
$eq: ["$files.isFree", false],
},
1,
0,
],
},
},
},
},
{
$addFields: {
"files.free": "$free",
"files.paid": "$paid",
},
},
{
$project: {
_id: 1,
name: 1,
files: 1,
price: 1,
},
},
]);
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