CODEWITHSUNDEEP
node.jsmongodbmongoose
Sajeetharan
Sajeetharan

Reputation: 222657

Mongodb - unknown top level operator: $elemMatch"

I have a collection which contains some documents as follows,

{
  "transactionId": 3432423,
  "reviews": [
    {
      "fromUser": {
        "userId": "5236aa1acd6e"
      },
      "toUser": {
        "userId": "0ec8db9544cc"
      },
      "rating": 4.3,
      "comment": ""
    },
    {
    "toUser": {
        "userId": "5236aa1acd6e",
        "email": "[email protected]",
        "firstName": "your",
        "lastName": "life"
      },
      "fromUser": {
        "userId": "0ec8db9544cc",
        "email": "[email protected]",
        "firstName": "my",
        "lastName": "life"
      },
      "rating": 4.3,
      "comment": ""
    }
  ]

}

i need to check if subdocument reviews present inside the document. i have used this query,

db.getCollection('_testCollection').find({  "$elemMatch": { "reviews": { "$exists": false } }})

it throws an error saying,

"errmsg" : "unknown top level operator: $elemMatch",

Upvotes: 2

Views: 9659

Answers (2)

JohnnyHK
JohnnyHK

Reputation: 312179

Neither $elemMatch or $exists is what you want to use to determine if reviews is an empty array.

Instead, either compare against []:

db.test.find({reviews: []})

Or use the $size operator:

db.test.find({reviews: {$size: 0}})

Upvotes: 4

hardy
hardy

Reputation: 901

From the Docs :-

The $elemMatch operator matches documents that contain an array field with at least one element that matches all the specified query criteria.

db.getCollection('_testCollection').find({  "reviews": {"$elemMatch" : { "$exists": false } }})

$exists :- true or false // depend on requirement

Thanks

Upvotes: 0

Related Questions