use $where in mongodb to get query length of array, because query $size not support $gt, $lt, $lte and $gte

query_array_legth_mongodb.js

db.test.insert({'name': 'rizky', 'abilities': ['eat', 'sleep', 'code']});
db.test.insert({'name': 'abdilah', 'abilities': ['drink']});
db.test.insert({'name': 'median', 'abilities': null});

condition_have_ability_more_than_2 = function(){
	return typeof(this.abilities) == "object" && this.abilities != null && this.abilities.length > 2;
}

// peoples have abilities more_than_2
db.test.find(condition_have_ability_more_than_2);

// update data
db.test.find(condition_have_ability_more_than_2).forEach(
    function(v){
        v['smart'] = true;
        db.test.save(v);
    }
);

// check success update or not
db.test.findOne({smart: true})