Can I $nin on the current projection in an aggregate pipeline - mongodb

Question

I have a directional graph to relate people to people, people to children, and people to pets. The relationship model looks like this:
module.exports = mongoose.model('Relationship', {
sourcePerson: {type: Schema.Types.ObjectId, ref: 'Person'},
targetPerson: {type: Schema.Types.ObjectId, ref: 'Person'},
targetChild: {type: Schema.Types.ObjectId, ref: 'Child'},
targetPet: {type: Schema.Types.ObjectId, ref: 'Pet'},
relationshipStatus: {
type: String,
enum: enums.relationshipStatus
}
});
The primary reason I am not using child documents via arrays off of the people is because the maintenance for that type of data model is too high and too strict. I know those statements contrast a little.
You see, if a couple is married then assumptions are made when adding relationships and the logical model becomes a bit more strict, but if they aren't then relationships are very loose and must be for the use case.
So, let's consider 3 people:
_id firstName lastName
1 Bob Smith
2 Jane Smith
3 Billy Bob
and their relationships:
sourcePerson targetPerson relationshipStatus
1 2 M
2 1 M
Take note that 3, Billy Bob, does not have a relationship to any people.
Now, I have a query I'm building that projects a profile for people. Specifically, are they married, do they have pets, and do they have children.
Thus far I've constructed the following aggregate:
db.people.aggregate([
{
$match: {
'_id': {
$in: db.relationships.distinct('sourcePerson', {
relationshipStatus: {
$eq: 'M'
}
})
}
}
},
{
$project: {
firstName: 1,
lastName: 1,
profile: {
married: {
$literal: true
}
}
}
},
{
$match: {
'_id': {
$in: db.relationships.distinct('sourcePerson', {
targetPet: {
$ne: null
}
})
}
}
},
{
$project: {
firstName: 1,
lastName: 1,
profile: {
married: 1,
pets: {
$literal: true
}
}
}
},
{
$match: {
'_id': {
$in: db.relationships.distinct('sourcePerson', {
targetChild: {
$ne: null
}
})
}
}
},
{
$project: {
firstName: 1,
lastName: 1,
profile: {
married: 1,
pets: 1,
children: {
$literal: true
}
}
}
}
])
The immediate problem I have is how can I perform a $nin on the _id of the Person using what I'm going to call the "current projection."
Specifically what I mean is this. If we take this snippet:
db.people.aggregate([
{
$match: {
'_id': {
$in: db.relationships.distinct('sourcePerson', {
relationshipStatus: {
$eq: 'M'
}
})
}
}
},
{
$project: {
firstName: 1,
lastName: 1,
profile: {
married: {
$literal: true
}
}
}
}
...
])
At this point I have a projection of all "married people". From this projection alone I can identify those that are "not married" if I could $nin the current projection.
I'm not sure this is even what I want.
If there is a better overall way, I'm totally open.
Looking forward to your feedback!