猫鼬聚合如何将多个集合映射到一个数组中 [英] mongoose aggregate how to map multiple collections into one Array
问题描述
我有四个不同的系列.从哪三个连成一个:
I have four different collections. From which three are connected to one:
Collection_A = {
_id: 1
name: A
includes: [
{
_id: 1,
includes_id: 222,
},
{
_id: 2,
includes_id: 333
}
]
}
Collection_B = {
_id: 222,
type: Computer,
name: Computer,
ref_id: 1
}
Collection_C = {
_id: 333,
type: Human,
name: Human,
ref_id: 1
}
Collection_D = {
_id: 444,
type: Animal,
name: Animal,
ref_id: 1
}
所以集合 A 可以在包含对象中包含集合 B、C 和 D.它包括至少一个集合.
So collection A can include Collection B, C and D in the includes object. It includes minimum one of the collections.
所以在集合A的includes对象中是includes_id，它是集合B、C和D中的_id.集合 A 中的 _id 是集合 B、C 和 D 中的 ref_id.
So in the includes object in Collection A is the includes_id, which is the _id in Collection B, C and D. The _id in Collection A is the ref_id in Collection B, C and D.
我现在的问题是，该聚合只需要最后一个映射的集合.
What my problem right now is, that aggregate takes only the last mapped collection.
我现在的代码如下:
Collection_A.aggregate([
{
$lookup: {
from: "collectionb",
localField: "includes.includes_id",
foreignField: "_id",
as: "colb",
},
},
{
$lookup: {
from: "collectionc",
localField: "includes.includes_id",
foreignField: "_id",
as: "colc",
},
},
{
$project: {
_id: 1,
status: 1,
type: 1,
includes_list: {
$map: {
input: "$includes",
as: "i",
in: {
$arrayElemAt: [
{
$filter: {
input: "$colb",
cond: {
$eq: ["$$this._id", "$$i.includes_id"],
},
},
},
0,
],
$arrayElemAt: [
{
$filter: {
input: "$colc",
cond: {
$eq: ["$$this._id", "$$i.includes_id"],
},
},
},
0,
],
},
},
},
},
},
]);
我试图在每次查找时都使 $lookup 相同，但它只使用最后一次查找的数据，而其他数据显示为空.所以我将 $lookup 设置为唯一的，并在 map 中放入了两个 in，但也显示了最后查找的数据，而其他的为 null.
I tried to make the $lookup as the same on every lookup, but so it only took the last looked up data, and the others where shown as null. So I made $lookup as unique, and put two ins in map, but then also the last looked up data was shown, and the others where null.
当我做这样的映射时:
includes_list: {
$map: {
input: "$icludes",
as: "i",
in: {
{
Col_A : {
$arrayElemAt: [
{
$filter: {
input: "$A",
cond: {
$eq: ["$$this._id", "$$i.includes"],
},
},
},
0,
],
},
Col_B : {
$arrayElemAt: [
{
$filter: {
input: "$B",
cond: {
$eq: ["$$this._id", "$$i.includes"],
},
},
},
0,
],
}
}
},
},
}
它有效.但没有正确的输出，因为我需要在一个数组中包含 includes_list.
It workes. But not with the right output, because I need includes_list within one array.
我想要的输出如下:
{
includes: [
{
_id: 1,
name: Computer,
includes_list: [
{
_id: 222,
type: Computer,
name: Computer,
ref_id: 1
},
{
_id: 333,
type: Human,
name: Human,
ref_id: 1
},
]
},
{
_id: 2,
name: Animal,
includes_list: [
{
_id: 333,
type: Human,
name: Human,
ref_id: 2
},
]
}
]
}
非常感谢您的帮助！
推荐答案
对于这种情况，$facet 帮助对传入的数据进行分类
For this kind of situation,
$facet help to categorize the incoming data
db.Collection_A.aggregate([
{ $unwind: "$includes },
{
"$facet": {
"joinB": [
{
"$lookup": {
"from": "Collection_B", "localField": "includes.includes_id",
"foreignField": "_id", "as": "includes.includes_list"
}
},
{
"$group": {
"_id": "$_id",
"name": { "$first": "$name" },
includes: { $push: "$includes" }
}
}
],
"joinC": [
{
"$lookup": {
"from": "Collection_C", "localField": "includes.includes_id",
"foreignField": "_id", "as": "includes.includes_list"
}
},
{
"$group": {
"_id": "$_id",
"name": { "$first": "$name" },
includes: { $push: "$includes" }
}
}
],
"joinD": [
{
"$lookup": {
"from": "Collection_D", "localField": "includes.includes_id",
"foreignField": "_id", "as": "includes.includes_list"
}
},
{
"$group": {
"_id": "$_id",
"name": { "$first": "$name" },
includes: { $push: "$includes" }
}
}
],
}
},
{
$project: {
combined: {
"$concatArrays": [ "$joinB", "$joinC", "$joinD" ]
}
}
},
{ "$unwind": "$combined" },
{
"$replaceRoot": { "newRoot": "$combined" }
},
{
"$project": {
_id: 1,
name: 1,
includes: {
$filter: {
input: "$includes",
cond: {
$ne: [ "$$this.includes_list",[] ]
}
}
}
}
}
])
工作 Mongo 游乐场
注意:我觉得这是你遵循的一种反模式.如果你在项目的早期阶段，如果我没记错的话最好改变结构.
Note: I feel this is kind of Anti pattern you follow. If you are in early stage of the project, better change the structure if I'm not mistaken.
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