CODEWITHSUNDEEP
javascriptnode.jsmongodbexpress
CaeSea
CaeSea

Reputation: 298

Using elemMatch to return one object from array node.js

I am trying to query a data collection to return just one object from an array of objects using elemMatch. I have this data:

[
{
    "_id": "5ba10e24e1e9f4062801ddeb",
    "user": {
        "_id": "5b9b9097650c3414ac96bacc",
        "firstName": "blah",
        "lastName": "blah blah",
        "email": "[email protected]"
    },
    "appointments": [
        {
            "date": "2018-09-18T14:39:36.949Z",
            "_id": "5ba10e28e1e9f4062801dded",
            "treatment": "LVL",
            "cost": 30
        },
        {
            "date": "2018-09-18T14:39:32.314Z",
            "_id": "5ba10e24e1e9f4062801ddec",
            "treatment": "LVL",
            "cost": 30
        }
    ],
    "__v": 1
}
]

I need to query the DB and pull out just one appointment depending on the id passed to params. I am using the code below based on the docs here.

router.get(
 "/booked/:app_id",
 passport.authenticate("jwt", { session: false }),
 (req, res) => {
  Appointment.find()
  .elemMatch("appointments", { id: req.params.app_id })
  .then(app => res.json(app));
 }
);

This is returning an empty array though when I test with postman. This is the first time I have used node.js and mongoDB so any help would be appreciated. Thanks.

Upvotes: 0

Views: 1123

Answers (1)

matthPen
matthPen

Reputation: 4363

You are using elemmatch as query operator, but you need to use it as projection operator

Change your function to this :

Appointment.find(
  {"appointments": {$elemMatch: {_id: req.params.app_id }}},
  {"appointments": {$elemMatch: {_id: req.params.app_id }}}
)

Why twice??

First object in find query param is $elemmatch query operator. It will return all documents, that have at least one entry matching _id in there appointments array. (but will return whole documents)

Second object (the same) is elemmatch projection oprator, which 'filters' appointments array and returns only the first matching element in array.

PS : cannot test this command. Try on your side

Upvotes: 2

Related Questions