Applying $exists to MongoDB aggregation - mongodb

Question

I have two mongo collections structured like so:
customers
{
_id: ObjectId,
name: String,
companyId: ObjectId
}
companies
{
_id: ObjectId,
name: String,
rights: [
add: boolean,
edit: boolean,
shop: boolean
]
}
So each customer has a companyId that lets us look up the companies.rights available. I need to get a list of which companies have customers but don't have the shop property at all.
So far I have this:
db.getCollection('customers').aggregate([
{
$match: {}
},
{
$lookup: {
from: 'companies',
localField: 'companyId',
foreignField: '_id',
as: 'company'
}
},
{
$project: {
companyId: '$company._id',
companyName: '$company.name',
shopSetting: '$company.rights.shop'
}
}
])
This seems to be working ok to give me all of the companies with their shop value (true or false). But what if I only want to see the companies that don't have the shop field existing at all? How would I modify this query to accomplish that? I've tried reading up on the $exists field in mongo, but this is all pretty new to me so I'm not sure where to apply it here.
Note: I need to query the companies from the customers collection because there are some companies without customers and I need this result to only be companies that are assigned to customers but don't have the rights.shop property existing

Answer 1

db.customers.aggregate([
{ $match: {} },
{
$lookup: {
from: "companies",
localField: "companyId",
foreignField: "_id",
as: "company",
pipeline: [
{
$match: {
$expr: {
$eq: [
{
$filter: {
input: "$rights",
as: "r",
cond: "$$r.shop"
}
},
[]
]
}
}
}
]
}
},
{
$project: {
companyId: "$company._id",
companyName: "$company.name",
shopSetting: "$company.rights.shop"
}
}
])
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