Mongoose Query to Find Unique Values - mongodb

Question

In my MongoDB backend I want to create an endpoint that returns all the unique values for a property called department. Now, if I were doing this in IntelliShell I would just do something like:
db.staffmembers.distinct( "department" )
This will return an array of all the values for department.
But how do you return all unique values within a Mongoose find() query like this one?
Staffmember.find({ name: 'john', age: { $gte: 18 }});
In other words, what would the syntax look like if I want to use a find() like above, to return all unique values for department within the "staffmembers" collection?

Answer 1

You can use .aggregate() and pass your condition into $match stage and then use $addToSet within $group to get unique values.
let result = await Staffmember.aggregate([
{ $match: { name: 'john', age: { $gte: 18 }} },
{ $group: { _id: null, departments: { $addToSet: "$department" } } }
]);

Answer 2

We can use find and distinct like this for the above scenario. Aggregate might be a little overkill. I have tried both the solutions below.
Staffmember.find({name: 'john', age: {$gte: 18}}).distinct('department',
function(error, departments) {
// departments is an array of all unique department names
}
);
Staffmember.distinct('department', {name:'john', age:{ $gte: 18 }},
function(error, departments) {
// departments is an array of all unique department names
}
);
This link just nails it with all different possibilities:
How do I query for distinct values in Mongoose?