Find object based on array element, return only matching array element?

Question

I have a Person object in mongoose, and that person object has multiple things (each thing has a unique ID).

person1 = {
  things[{id: 1, name: 'one'},{id:2, name: 'two'}]
}
person2 = {
  things[{id: 3, name: 'three'},{id:4, name: 'four'}]
}

then query:

Person.findOne({'things.id': 2},{'things.$': 1}, function(err, person) { ...

This works great but I am searching through all Person objects (which there could be a lot of). In this case I know the id of the Person I need and some unique id of a 'thing'. Its probably a lot faster to get the Person by id:

Person.findById(personId, function(err, person) { ...

Then loop over all the things to find the right one:

var thing
person.things.forEach(function(t) {
  if (t.id == thingId) {
    thing = t;
  }
});

What I am wondering is if there is a better way. I.E. can I query the Person collection by id to get just one Person then filter out just the thing I am looking for (without the ugly loop)?

The $ is a positional operator. You can find more details about it in the Mongo docs ;) — Preview
– Preview, Commented Oct 23, 2014 at 13:38

JohnnyHK · Accepted Answer · 2013-03-05 02:34:07Z

19

You can include both id terms in a single query and the single element projection will still work:

Person.findOne({_id: personId, 'things.id': 2}, {'things.$': 1}, 
    function(err, person) { ...

answered Mar 5, 2013 at 2:34

JohnnyHK

313k70 gold badges632 silver badges479 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

lostintranslation Over a year ago

So that will query on Person first (which should be fast), then on a specific thing for that person? That is awesome, thanks!

Ulysses Alves Over a year ago

So does this mean that the person object will be returned with only one element in the things array, that being the thing we are looking for in the query?

Ulysses Alves Over a year ago

Nice. I am looking now for a way to do this but with findOneAndUpdate, because I need to update only a specific element of a document array. Do you have any ideas on how to accomplish this?

JohnnyHK Over a year ago

@UlyssesAlves See stackoverflow.com/questions/17678327/…

Collectives™ on Stack Overflow

Find object based on array element, return only matching array element?

1 Answer 1

4 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related