Merge $lookup value inside objects nested in array mongoose - mongodb

Question

So I have 2 models user & form.
User Schema
firstName: {
type: String,
required: true,
},
lastName: {
type: String,
required: true,
},
email: {
type: String,
required: true,
}
Form Schema
approvalLog: [
{
attachments: {
type: [String],
},
by: {
type: ObjectId,
},
comment: {
type: String,
},
date: {
type: Date,
},
},
],
userId: {
type: ObjectId,
required: true,
},
... other form parameters
When returning a form, I'm trying to aggregate the user info of every user in the approvalLog into their respective objects as below.
{
...other form info
approvalLog: [
{
attachments: [],
_id: '619cc4953de8413b548f61a6',
by: '619cba9cd64af530448b6347',
comment: 'visit store for disburement',
date: '2021-11-23T10:38:13.565Z',
user: {
_id: '619cba9cd64af530448b6347',
firstName: 'admin',
lastName: 'user',
email: 'admin#mail.com',
},
},
{
attachments: [],
_id: '619cc4ec3ea3e940a42b2d01',
by: '619cbd7b3de8413b548f61a0',
comment: '',
date: '2021-11-23T10:39:40.168Z',
user: {
_id: '619cbd7b3de8413b548f61a0',
firstName: 'sam',
lastName: 'ben',
email: 'sb#mail.com',
},
},
{
attachments: [],
_id: '61a9deab8f472c52d8bac095',
by: '61a87fd93dac9b209096ed94',
comment: '',
date: '2021-12-03T09:08:59.479Z',
user: {
_id: '61a87fd93dac9b209096ed94',
firstName: 'john',
lastName: 'doe',
email: 'jd#mail.com',
},
},
],
}
My current code is
Form.aggregate([
{
$lookup: {
from: 'users',
localField: 'approvalLog.by',
foreignField: '_id',
as: 'approvedBy',
},
},
{ $addFields: { 'approvalLog.user': { $arrayElemAt: ['$approvedBy', 0] } } },
])
but it only returns the same user for all objects. How do I attach the matching user for each index?
I've also tried
Form.aggregate([
{
$lookup: {
from: 'users',
localField: 'approvalLog.by',
foreignField: '_id',
as: 'approvedBy',
},
},
{
$addFields: {
approvalLog: {
$map: {
input: { $zip: { inputs: ['$approvalLog', '$approvedBy'] } },
in: { $mergeObjects: '$$this' },
},
},
},
},
])
This adds the right user to their respective objects, but I can only add the to the root object and not a new one.

Answer 1

You can try the approach,
$map to iterate loop of approvalLog
$filter to iterate loop of approvedBy array and search for user id by
$arrayElemAt to get first element from above filtered result
$mergeObjects to merge current object properties of approvalLog and filtered user
$$REMOVE don't need approvedBy now
await Form.aggregate([
{
$lookup: {
from: "users",
localField: "approvalLog.by",
foreignField: "_id",
as: "approvedBy"
}
},
{
$addFields: {
approvalLog: {
$map: {
input: "$approvalLog",
as: "a",
in: {
$mergeObjects: [
"$$a",
{
user: {
$arrayElemAt: [
{
$filter: {
input: "$approvedBy",
cond: { $eq: ["$$a.by", "$$this._id"] }
}
},
0
]
}
}
]
}
}
},
approvedBy: "$$REMOVE"
}
}
])
Playground
The second approach using $unwind,
$unwind deconstruct the approvalLog array
$lookup with user collection
$addFields and $arrayElemAt to get first element from lookup result
$group by _id and reconstruct the approvalLog array and get first value of other required properties
await Form.aggregate([
{ $unwind: "$approvalLog" },
{
$lookup: {
from: "users",
localField: "approvalLog.by",
foreignField: "_id",
as: "approvalLog.user"
}
},
{
$addFields: {
"approvalLog.user": {
$arrayElemAt: ["$approvalLog.user", 0]
}
}
},
{
$group: {
_id: "$_id",
approvalLog: { $push: "$approvalLog" },
userId: { $first: "$userId" },
// add your other properties like userId
}
}
])
Playground