How to query in mongodb with nested json

Question

I have this json file:

 {
  "id" : 100,
  "boolean": 1,
  "color": 2,
  "MYtable": [{"a":1, "b":2}],
  "number": 4,
  "string": 5
}
{
  "id" : 200,
  "boolean": 1,
  "color": 22,
  "MYtable": [{"a":10, "b":20,"c":30}],
  "number": 42,
  "string": 52
}
{
  "id" : 300,
  "boolean": 13,
  "color": 223,
  "MYtable": [],
  "number": 423,
  "string": 523
}

Using a mongodb query I would like to get only the elements that have MYtable of size 1 or larger. For example in the above json I would only get the elements with id 100 and 200.

MYcollection is my database's collection.

I tried this:

MYcollection.find({ "MYtable": {"$size": {"$gt" :1}}})

and also this:

MYcollection.find({"$where" : "this.MYtable.length > 1"})

But it didn't work. What am I missing?

Answer 1

You can use $expr with $size to filter the documents

db.col.find({$expr : {$gt : [{$size : "$MYtable"},1]}})

try using $expr , below from the documentation

$expr is faster than $where because it does not execute JavaScript and should be preferred where possible.

EDIT -1

you may need to change your document structure to store the array elements

the below works with you document structure by converting the array element at 0 to an array to compare the size

db.col.find({$expr:{$gt:[{$size:{$ifNull:[{"$objectToArray":{$arrayElemAt:[{$ifNull:["$MYtable",[]]},0]}},[]]}},1]}})

Answer 2

There is a imho hacky but often seen way:

db.collection.find({'yourArrayField.1' : {$exists : true}}

I am not sure currently, if there can be undefined fields between existing ones, but it is a simple solution that might work for you.