在MongoDb Schema中只获取数组中所需的元素

Question

我只想从notes数组中获取那些与notes中tags数组中给定的tag匹配的元素。

例如：如果我只想从标签数组中有lrn标签的notes数组中获取那些注释，但我得到的要么是整个对象，要么是第一个匹配的注释。

我的模式：

const mongoose = require('mongoose');
const noteSchema = new mongoose.Schema({
user : {
type: String,
required: true,
unique : true
},
notes : {
type : [{
title : {
type: String,
required: true
},
tags : {
type : [String],
required: true
},
note: {
type: String,
required: true
}
}],
required: true
}
});
const Notebook = mongoose.model('NOTEBOOK', noteSchema);
module.exports = Notebook;

我的样本数据：

{ _id: ObjectId("621c3a41fa2fe3c07f43edc9"),
user: '620c81434d8a65c1aa36e0d4',
notes: 
[ { title: 'Eraning',
tags: [ 'ern', 'lrn', 'dik', 'pik', 'sik' ],
note: 'Prior to his return, Craig worked at NeXT, followed by Apple, and then spent a decade at Ariba, an internet e-commerce pioneer where he held several roles including chief technology officer.nPrior to his return, Craig worked at NeXT, followed by Apple, and then spent a decade at Ariba, an internet e-commerce pioneer where he held several roles including chief technology officer.n',
_id: ObjectId("62205a32bab7aed6315195e9") },
{ title: 'Lerningngs',
tags: [ 'lrn', 'eat', 'drink' ],
note: 'Prior to his return, Craig worked at NeXT, followed by Apple, and then spent a decade at Ariba, an internet e-commerce pioneer where he held several roles including chief technology officer.n',
_id: ObjectId("6220583cbab7aed63151958b") },
{ title: 'Learning',
tags: [ 'learn', 'eran', 'buy', 'sell' ],
note: 'Prior to his return, Craig worked at NeXT, followed by Apple, and then spent a decade at Ariba, an internet e-commerce pioneer where he held several roles including chief technology officer.Solving DSA from Maths.in and SolveMaths.org using great techniques by INDIA and RUSSIA.n',
_id: ObjectId("6220532dbab7aed631519531") },
{ title: 'Biology',
tags: [ 'tissue', 'cell', 'myto', 'energy', 'glycogen', 'hydrogen' ],
note: 'Prior to his return, Craig worked at NeXT, followed by Apple, and then spent a decade at Ariba, an internet e-commerce pioneer where he held several roles including chief technology officer.Solving DSA from Maths.in and SolveMaths.org using great techniques by INDIA and RUSSIA.nn',
_id: ObjectId("621f88d4c189c6b5501c3d5f") },
{ title: 'Chemistry',
tags: [ 'this', 'is', 'great', 'thing', 'to', 'do', 'by', 'time' ],
note: '          Prior to his return, Craig worked at NeXT, followed by Apple, n          and then spent a decade at Ariba, an internet e-commerce pioneer n          where he held several roles including chief technology officer.n',
_id: ObjectId("621f85e9c189c6b5501c3d49") },
{ title: 'Physics',
tags: 
[ 'newtonlawsofmotion',
'ktg',
'thermo',
'fluid',
'mechanice',
'bernaulii' ],
note: 'P' + hrg + 1/2rv^2 = constant',
_id: ObjectId("621f8520c189c6b5501c3d3f") },
{ title: 'Maths',
tags: [ 'trignometry', 'llp', 'continuity', 'tags', 'circle' ],
note: 'Solving DSA from Maths.in and SolveMaths.org using great techniques by INDIA and RUSSIA.',
_id: ObjectId("621f84d7c189c6b5501c3d37") },
{ title: 'DSA from Net',
tags: [ 'dp', 'stack', 'queue', 'heaps', 'sorting' ],
note: 'Solving DSA from Leetcode.in and GeeksforGeeks.org',
_id: ObjectId("621c3a41fa2fe3c07f43edca") } ],
__v: 7 }

Answer 1

您可以使用$filter获取给定标签的文档，如下所示：

Notebook.findOne({
user: "620c81434d8a65c1aa36e0d4" // user ID
},
{
notes: {
$filter: {
input: "$notes",
as: "note",
cond: {
$in: [
"ern", // Tag to search
"$$note.tags"
]
}
}
}
})

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