$size operator requires an array of 1 operand

[ledomi]

Hi All,

I think that validation for aggregation with $size is invalid. Step by step:

Fongo version: 2.1.1

My collection:

[{
		"_id": 5b894357a0c84d5a5d221f25,
		"conferenceName": "myFirstConference",
		"startDate": 1535722327,
		"endDate": 1535722420,
		"participants": [{
				"name": "user1",
				"origin": "internal",
				"ip": "192.168.0.2"
			}, {
				"name": "user2",
				"origin": "external",
				"ip": "172.20.0.3"
			},{
				"name": "user3",
				"origin": "internal",
				"ip": "192.168.0.3"
			},
		]
	}
]

My mongo query that works is :

db.collection.aggregate([{
		"$project": {
			"conferenceName": 1,
			"startDate": 1,
			"endDate": 1,
			"internalUsersCount": {
				"$size": {
					"$filter": {
						"input": "$participants",
						"as": "part",
						"cond": {
							"$eq": ["$$part.origin", "internal"]
						}
					}
				}
			}
		}
	}])

In that case as an input we have a LinkedHasMap not List but parsing was implementet as below

class ProjectedSize 
.....
 private String parseOperand(Object value) {
      if (!(value instanceof String) && (!(value instanceof List) || ((List) value).size() != 1)) {
        errorResult(coll, 16020, "the " + keyword + " operator requires an array of 1 operand");
      }
}

But it doesn't work in fongo, Anybody can help ?