MongoDB Remove or Limit fields conditional aggregation - mongodb

Question

I am having some issue writing a find/aggregate mongo query where my requirement is to get all the documents but having condition like:
Suppose I have 2 documents:
{
_id: 5ccaa76939d95d395791efd2,
name: 'John Doe',
email: 'john.doe#foobar.com',
private: true
}
{
_id: 5ccaa76939d95d395791efd2,
name: 'Jane Doe',
email: 'jane.doe#foobar.com',
private: false
}
Now the query I am trying to get my head around is if the field private is true then when I query I must get all documents except email fields not included if private is true, like this:
{
_id: 5ccaa76939d95d395791efd2,
name: 'John Doe',
private: true
}
{
_id: 5ccaa76939d95d395791efd2,
name: 'Jane Doe',
email: 'jane.doe#foobar.com',
private: false
}
Tried $redact, $cond, $$PRUNE, $$DESCEND in aggregate() as well as came across $$REMOVE (looks like it is newest feature) but unable to get the required output. Please help me out with the Query

Answer 1

You can use $$REMOVE to remove a field from returned documents.
db.collection.aggregate([
{ "$addFields": {
"email": {
"$cond": [
{ "$eq": ["$private", true] },
"$$REMOVE",
"$email"
]
}
}}
])
MongoPlayground

Answer 2

Thank you Anthony Winzlet, his solution worked like a charm.
If anyone faces same problem and requires to include more than 1 fields, I am doing so by writing this method:
function condition(privateFieldLimitationArray, publicFieldLimitationArray) {
const condition = {};
privateFieldLimitationArray.map((d, i) => {
condition[d] = {
"$cond": [
{ "$eq": ["$private", true] },
"$$REMOVE",
publicFieldLimitationArray.includes(d) ? '$$REMOVE' : '$'+d
]
}
});
return condition;
}
Then, you can use the above function like:
const privateLimitationArray = ['updatedAt', 'createdAt', 'email', 'lname', 'friendslist', '__v'];
const publicLimitationArray = ['updatedAt', 'createdAt', '__v'];
YourModel.aggregate([
{
$match: {
// Your query to find by
}
}, {
"$addFields": condition(privateLimitationArray, publicLimitationArray)
}
])
.then(result => {
// handle result
})
.catch(error => {
// handle error
});