Mongodb$unwind删除对象。如果$lookup没有';我没有参考资料
如果国家没有参考州和城市$“展开”将从集合中删除国家/地区名称 预期输出为Mongodb,即使国家没有任何州和城市引用,Mongodb也应返回国家名称 国家/地区系列:Mongodb$unwind删除对象。如果$lookup没有';我没有参考资料,mongodb,mongoose,mongodb-query,Mongodb,Mongoose,Mongodb Query,如果国家没有参考州和城市$“展开”将从集合中删除国家/地区名称 预期输出为Mongodb,即使国家没有任何州和城市引用,Mongodb也应返回国家名称 国家/地区系列: [ { "_id": "5d052c76df076d23a48d4a3b", "name": "India" }, { "_id": "5d052c76df076d23a48d4b07", "name": "Indonesia" }, { "_id": "5d052c7
[
{
"_id": "5d052c76df076d23a48d4a3b",
"name": "India"
},
{
"_id": "5d052c76df076d23a48d4b07",
"name": "Indonesia"
},
{
"_id": "5d052c76df076d23a48d22f4",
"name": "Iran"
}
]
[
{
"_id": "5d2236c37ed1112b3cc41397",
"name": "Andaman and Nicobar Islands",
"countryId": "5d052c76df076d23a48d4a3b"
},
{
"_id": "5d2236c37ed1112b3cc41398",
"name": "Andhra Pradesh",
"countryId": "5d052c76df076d23a48d4a3b"
}
]
[
{
"name": "Port Blair",
"stateId": "5d2236c37ed1112b3cc41397"
},
{
"name": "Adoni",
"stateId": "5d2236c37ed1112b3cc41398"
}
Country.aggregate([
{
$lookup:{
from: 'states',
localField:'_id',
foreignField:'countryId',
as:'states'
}
},
{
$unwind: {
path: "$states"
}
},
{
$lookup:{
from: 'cities',
localField:'states._id',
foreignField:'stateId',
as:'states.cities'
}
},
{
$group: {
_id: {
_id: '$_id',
name: '$name'
},
states: {
$push: '$states'
}
}
},
{
$project: {
_id: '$_id._id',
name: '$_id.name',
states: 1
}
}
])
[
{
"_id":"5d052c76df076d23a48d4a3b",
"name":"India",
"states":[
{
"_id":"5d2236c37ed1112b3cc41397",
"name":"Andaman and Nicobar Islands",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Port Blair",
"stateId":"5d2236c37ed1112b3cc41397"
}
]
},
{
"_id":"5d2236c37ed1112b3cc41398",
"name":"Andhra Pradesh",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Adoni",
"stateId":"5d2236c37ed1112b3cc41398"
}
]
}
]
}
]
[
{
"_id":"5d052c76df076d23a48d4a3b",
"name":"India",
"states":[
{
"_id":"5d2236c37ed1112b3cc41397",
"name":"Andaman and Nicobar Islands",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Port Blair",
"stateId":"5d2236c37ed1112b3cc41397"
}
]
},
{
"_id":"5d2236c37ed1112b3cc41398",
"name":"Andhra Pradesh",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Adoni",
"stateId":"5d2236c37ed1112b3cc41398"
}
]
}
]
},
{
"_id":"5d052c76df076d23a48d4b07",
"name":"Indonesia",
"states":[
]
},
{
"_id":"5d052c76df076d23a48d22f4",
"name":"Iran",
"states":[
]
}
]
状态集合:
[
{
"_id": "5d052c76df076d23a48d4a3b",
"name": "India"
},
{
"_id": "5d052c76df076d23a48d4b07",
"name": "Indonesia"
},
{
"_id": "5d052c76df076d23a48d22f4",
"name": "Iran"
}
]
[
{
"_id": "5d2236c37ed1112b3cc41397",
"name": "Andaman and Nicobar Islands",
"countryId": "5d052c76df076d23a48d4a3b"
},
{
"_id": "5d2236c37ed1112b3cc41398",
"name": "Andhra Pradesh",
"countryId": "5d052c76df076d23a48d4a3b"
}
]
[
{
"name": "Port Blair",
"stateId": "5d2236c37ed1112b3cc41397"
},
{
"name": "Adoni",
"stateId": "5d2236c37ed1112b3cc41398"
}
Country.aggregate([
{
$lookup:{
from: 'states',
localField:'_id',
foreignField:'countryId',
as:'states'
}
},
{
$unwind: {
path: "$states"
}
},
{
$lookup:{
from: 'cities',
localField:'states._id',
foreignField:'stateId',
as:'states.cities'
}
},
{
$group: {
_id: {
_id: '$_id',
name: '$name'
},
states: {
$push: '$states'
}
}
},
{
$project: {
_id: '$_id._id',
name: '$_id.name',
states: 1
}
}
])
[
{
"_id":"5d052c76df076d23a48d4a3b",
"name":"India",
"states":[
{
"_id":"5d2236c37ed1112b3cc41397",
"name":"Andaman and Nicobar Islands",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Port Blair",
"stateId":"5d2236c37ed1112b3cc41397"
}
]
},
{
"_id":"5d2236c37ed1112b3cc41398",
"name":"Andhra Pradesh",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Adoni",
"stateId":"5d2236c37ed1112b3cc41398"
}
]
}
]
}
]
[
{
"_id":"5d052c76df076d23a48d4a3b",
"name":"India",
"states":[
{
"_id":"5d2236c37ed1112b3cc41397",
"name":"Andaman and Nicobar Islands",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Port Blair",
"stateId":"5d2236c37ed1112b3cc41397"
}
]
},
{
"_id":"5d2236c37ed1112b3cc41398",
"name":"Andhra Pradesh",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Adoni",
"stateId":"5d2236c37ed1112b3cc41398"
}
]
}
]
},
{
"_id":"5d052c76df076d23a48d4b07",
"name":"Indonesia",
"states":[
]
},
{
"_id":"5d052c76df076d23a48d22f4",
"name":"Iran",
"states":[
]
}
]
城市系列:
[
{
"_id": "5d052c76df076d23a48d4a3b",
"name": "India"
},
{
"_id": "5d052c76df076d23a48d4b07",
"name": "Indonesia"
},
{
"_id": "5d052c76df076d23a48d22f4",
"name": "Iran"
}
]
[
{
"_id": "5d2236c37ed1112b3cc41397",
"name": "Andaman and Nicobar Islands",
"countryId": "5d052c76df076d23a48d4a3b"
},
{
"_id": "5d2236c37ed1112b3cc41398",
"name": "Andhra Pradesh",
"countryId": "5d052c76df076d23a48d4a3b"
}
]
[
{
"name": "Port Blair",
"stateId": "5d2236c37ed1112b3cc41397"
},
{
"name": "Adoni",
"stateId": "5d2236c37ed1112b3cc41398"
}
Country.aggregate([
{
$lookup:{
from: 'states',
localField:'_id',
foreignField:'countryId',
as:'states'
}
},
{
$unwind: {
path: "$states"
}
},
{
$lookup:{
from: 'cities',
localField:'states._id',
foreignField:'stateId',
as:'states.cities'
}
},
{
$group: {
_id: {
_id: '$_id',
name: '$name'
},
states: {
$push: '$states'
}
}
},
{
$project: {
_id: '$_id._id',
name: '$_id.name',
states: 1
}
}
])
[
{
"_id":"5d052c76df076d23a48d4a3b",
"name":"India",
"states":[
{
"_id":"5d2236c37ed1112b3cc41397",
"name":"Andaman and Nicobar Islands",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Port Blair",
"stateId":"5d2236c37ed1112b3cc41397"
}
]
},
{
"_id":"5d2236c37ed1112b3cc41398",
"name":"Andhra Pradesh",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Adoni",
"stateId":"5d2236c37ed1112b3cc41398"
}
]
}
]
}
]
[
{
"_id":"5d052c76df076d23a48d4a3b",
"name":"India",
"states":[
{
"_id":"5d2236c37ed1112b3cc41397",
"name":"Andaman and Nicobar Islands",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Port Blair",
"stateId":"5d2236c37ed1112b3cc41397"
}
]
},
{
"_id":"5d2236c37ed1112b3cc41398",
"name":"Andhra Pradesh",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Adoni",
"stateId":"5d2236c37ed1112b3cc41398"
}
]
}
]
},
{
"_id":"5d052c76df076d23a48d4b07",
"name":"Indonesia",
"states":[
]
},
{
"_id":"5d052c76df076d23a48d22f4",
"name":"Iran",
"states":[
]
}
]
]
查询:
[
{
"_id": "5d052c76df076d23a48d4a3b",
"name": "India"
},
{
"_id": "5d052c76df076d23a48d4b07",
"name": "Indonesia"
},
{
"_id": "5d052c76df076d23a48d22f4",
"name": "Iran"
}
]
[
{
"_id": "5d2236c37ed1112b3cc41397",
"name": "Andaman and Nicobar Islands",
"countryId": "5d052c76df076d23a48d4a3b"
},
{
"_id": "5d2236c37ed1112b3cc41398",
"name": "Andhra Pradesh",
"countryId": "5d052c76df076d23a48d4a3b"
}
]
[
{
"name": "Port Blair",
"stateId": "5d2236c37ed1112b3cc41397"
},
{
"name": "Adoni",
"stateId": "5d2236c37ed1112b3cc41398"
}
Country.aggregate([
{
$lookup:{
from: 'states',
localField:'_id',
foreignField:'countryId',
as:'states'
}
},
{
$unwind: {
path: "$states"
}
},
{
$lookup:{
from: 'cities',
localField:'states._id',
foreignField:'stateId',
as:'states.cities'
}
},
{
$group: {
_id: {
_id: '$_id',
name: '$name'
},
states: {
$push: '$states'
}
}
},
{
$project: {
_id: '$_id._id',
name: '$_id.name',
states: 1
}
}
])
[
{
"_id":"5d052c76df076d23a48d4a3b",
"name":"India",
"states":[
{
"_id":"5d2236c37ed1112b3cc41397",
"name":"Andaman and Nicobar Islands",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Port Blair",
"stateId":"5d2236c37ed1112b3cc41397"
}
]
},
{
"_id":"5d2236c37ed1112b3cc41398",
"name":"Andhra Pradesh",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Adoni",
"stateId":"5d2236c37ed1112b3cc41398"
}
]
}
]
}
]
[
{
"_id":"5d052c76df076d23a48d4a3b",
"name":"India",
"states":[
{
"_id":"5d2236c37ed1112b3cc41397",
"name":"Andaman and Nicobar Islands",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Port Blair",
"stateId":"5d2236c37ed1112b3cc41397"
}
]
},
{
"_id":"5d2236c37ed1112b3cc41398",
"name":"Andhra Pradesh",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Adoni",
"stateId":"5d2236c37ed1112b3cc41398"
}
]
}
]
},
{
"_id":"5d052c76df076d23a48d4b07",
"name":"Indonesia",
"states":[
]
},
{
"_id":"5d052c76df076d23a48d22f4",
"name":"Iran",
"states":[
]
}
]
输出:
[
{
"_id": "5d052c76df076d23a48d4a3b",
"name": "India"
},
{
"_id": "5d052c76df076d23a48d4b07",
"name": "Indonesia"
},
{
"_id": "5d052c76df076d23a48d22f4",
"name": "Iran"
}
]
[
{
"_id": "5d2236c37ed1112b3cc41397",
"name": "Andaman and Nicobar Islands",
"countryId": "5d052c76df076d23a48d4a3b"
},
{
"_id": "5d2236c37ed1112b3cc41398",
"name": "Andhra Pradesh",
"countryId": "5d052c76df076d23a48d4a3b"
}
]
[
{
"name": "Port Blair",
"stateId": "5d2236c37ed1112b3cc41397"
},
{
"name": "Adoni",
"stateId": "5d2236c37ed1112b3cc41398"
}
Country.aggregate([
{
$lookup:{
from: 'states',
localField:'_id',
foreignField:'countryId',
as:'states'
}
},
{
$unwind: {
path: "$states"
}
},
{
$lookup:{
from: 'cities',
localField:'states._id',
foreignField:'stateId',
as:'states.cities'
}
},
{
$group: {
_id: {
_id: '$_id',
name: '$name'
},
states: {
$push: '$states'
}
}
},
{
$project: {
_id: '$_id._id',
name: '$_id.name',
states: 1
}
}
])
[
{
"_id":"5d052c76df076d23a48d4a3b",
"name":"India",
"states":[
{
"_id":"5d2236c37ed1112b3cc41397",
"name":"Andaman and Nicobar Islands",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Port Blair",
"stateId":"5d2236c37ed1112b3cc41397"
}
]
},
{
"_id":"5d2236c37ed1112b3cc41398",
"name":"Andhra Pradesh",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Adoni",
"stateId":"5d2236c37ed1112b3cc41398"
}
]
}
]
}
]
[
{
"_id":"5d052c76df076d23a48d4a3b",
"name":"India",
"states":[
{
"_id":"5d2236c37ed1112b3cc41397",
"name":"Andaman and Nicobar Islands",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Port Blair",
"stateId":"5d2236c37ed1112b3cc41397"
}
]
},
{
"_id":"5d2236c37ed1112b3cc41398",
"name":"Andhra Pradesh",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Adoni",
"stateId":"5d2236c37ed1112b3cc41398"
}
]
}
]
},
{
"_id":"5d052c76df076d23a48d4b07",
"name":"Indonesia",
"states":[
]
},
{
"_id":"5d052c76df076d23a48d22f4",
"name":"Iran",
"states":[
]
}
]
预期输出:
[
{
"_id": "5d052c76df076d23a48d4a3b",
"name": "India"
},
{
"_id": "5d052c76df076d23a48d4b07",
"name": "Indonesia"
},
{
"_id": "5d052c76df076d23a48d22f4",
"name": "Iran"
}
]
[
{
"_id": "5d2236c37ed1112b3cc41397",
"name": "Andaman and Nicobar Islands",
"countryId": "5d052c76df076d23a48d4a3b"
},
{
"_id": "5d2236c37ed1112b3cc41398",
"name": "Andhra Pradesh",
"countryId": "5d052c76df076d23a48d4a3b"
}
]
[
{
"name": "Port Blair",
"stateId": "5d2236c37ed1112b3cc41397"
},
{
"name": "Adoni",
"stateId": "5d2236c37ed1112b3cc41398"
}
Country.aggregate([
{
$lookup:{
from: 'states',
localField:'_id',
foreignField:'countryId',
as:'states'
}
},
{
$unwind: {
path: "$states"
}
},
{
$lookup:{
from: 'cities',
localField:'states._id',
foreignField:'stateId',
as:'states.cities'
}
},
{
$group: {
_id: {
_id: '$_id',
name: '$name'
},
states: {
$push: '$states'
}
}
},
{
$project: {
_id: '$_id._id',
name: '$_id.name',
states: 1
}
}
])
[
{
"_id":"5d052c76df076d23a48d4a3b",
"name":"India",
"states":[
{
"_id":"5d2236c37ed1112b3cc41397",
"name":"Andaman and Nicobar Islands",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Port Blair",
"stateId":"5d2236c37ed1112b3cc41397"
}
]
},
{
"_id":"5d2236c37ed1112b3cc41398",
"name":"Andhra Pradesh",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Adoni",
"stateId":"5d2236c37ed1112b3cc41398"
}
]
}
]
}
]
[
{
"_id":"5d052c76df076d23a48d4a3b",
"name":"India",
"states":[
{
"_id":"5d2236c37ed1112b3cc41397",
"name":"Andaman and Nicobar Islands",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Port Blair",
"stateId":"5d2236c37ed1112b3cc41397"
}
]
},
{
"_id":"5d2236c37ed1112b3cc41398",
"name":"Andhra Pradesh",
"countryId":"5d052c76df076d23a48d4a3b",
"cities":[
{
"name":"Adoni",
"stateId":"5d2236c37ed1112b3cc41398"
}
]
}
]
},
{
"_id":"5d052c76df076d23a48d4b07",
"name":"Indonesia",
"states":[
]
},
{
"_id":"5d052c76df076d23a48d22f4",
"name":"Iran",
"states":[
]
}
]
只需将“preserveNullAndEmptyArrays:true”添加到$unwind
Country.aggregate([
{
$lookup:{
from: 'states',
localField:'_id',
foreignField:'countryId',
as:'states'
}
},
{
$unwind: {
path: "$states",
preserveNullAndEmptyArrays: true
}
},
{
$lookup:{
from: 'cities',
localField:'states._id',
foreignField:'stateId',
as:'states.cities'
}
},
{
$group: {
_id: {
_id: '$_id',
name: '$name'
},
states: {
$push: '$states'
}
}
},
{
$project: {
_id: '$_id._id',
name: '$_id.name',
states: 1
}
}
])
输出
[
{
"states" : [
{
"cities" : []
}
],
"_id" : "5d052c76df076d23a48d22f4",
"name" : "Iran"
},
{
"states" : [
{
"cities" : []
}
],
"_id" : "5d052c76df076d23a48d4b07",
"name" : "Indonesia"
},
{
"states" : [
{
"_id" : "5d2236c37ed1112b3cc41397",
"name" : "Andaman and Nicobar Islands",
"countryId" : "5d052c76df076d23a48d4a3b",
"cities" : [
{
"_id" : ObjectId("5d38ccb6f9c5fa48bf099027"),
"name" : "Port Blair",
"stateId" : "5d2236c37ed1112b3cc41397"
}
]
},
{
"_id" : "5d2236c37ed1112b3cc41398",
"name" : "Andhra Pradesh",
"countryId" : "5d052c76df076d23a48d4a3b",
"cities" : [
{
"_id" : ObjectId("5d38ccbcf9c5fa48bf09902a"),
"name" : "Adoni",
"stateId" : "5d2236c37ed1112b3cc41398"
}
]
}
],
"_id" : "5d052c76df076d23a48d4a3b",
"name" : "India"
}
]
只需将“preserveNullAndEmptyArrays:true”添加到$unwind
Country.aggregate([
{
$lookup:{
from: 'states',
localField:'_id',
foreignField:'countryId',
as:'states'
}
},
{
$unwind: {
path: "$states",
preserveNullAndEmptyArrays: true
}
},
{
$lookup:{
from: 'cities',
localField:'states._id',
foreignField:'stateId',
as:'states.cities'
}
},
{
$group: {
_id: {
_id: '$_id',
name: '$name'
},
states: {
$push: '$states'
}
}
},
{
$project: {
_id: '$_id._id',
name: '$_id.name',
states: 1
}
}
])
输出
[
{
"states" : [
{
"cities" : []
}
],
"_id" : "5d052c76df076d23a48d22f4",
"name" : "Iran"
},
{
"states" : [
{
"cities" : []
}
],
"_id" : "5d052c76df076d23a48d4b07",
"name" : "Indonesia"
},
{
"states" : [
{
"_id" : "5d2236c37ed1112b3cc41397",
"name" : "Andaman and Nicobar Islands",
"countryId" : "5d052c76df076d23a48d4a3b",
"cities" : [
{
"_id" : ObjectId("5d38ccb6f9c5fa48bf099027"),
"name" : "Port Blair",
"stateId" : "5d2236c37ed1112b3cc41397"
}
]
},
{
"_id" : "5d2236c37ed1112b3cc41398",
"name" : "Andhra Pradesh",
"countryId" : "5d052c76df076d23a48d4a3b",
"cities" : [
{
"_id" : ObjectId("5d38ccbcf9c5fa48bf09902a"),
"name" : "Adoni",
"stateId" : "5d2236c37ed1112b3cc41398"
}
]
}
],
"_id" : "5d052c76df076d23a48d4a3b",
"name" : "India"
}
]
有没有办法删除城市空结果?有没有办法删除城市空结果?