Return null default value if no result found

Question

I have a collection that looks like this:

{  
\"value\" : \"20\",
\"type\" : \"square\",
\"name\" : \"form1\"
}
{
\"value\" : \"24\",
\"type\" : \"circle\",
         


        

Answer 1

You can use below aggregation

Mongodb doesn't produce the result if there is not $matched data found with the query.

But you can use $facet aggregation which processes multiple aggregation pipeline within single stage.

So first use $facet to get the $matched documents and use $projection if no ($ifNull) data found.

let searchTerm = "form2"

db.myCollec.aggregate([
  { "$facet": {
    "data": [
      { "$match": { "name": searchTerm  }},
      { "$project": { "name": 1, "type": 1, "_id": 0 }}
    ]
  }},
  { "$project": {
    "name": {
      "$ifNull": [{ "$arrayElemAt": ["$data.name", 0] }, searchTerm ]
    },
    "type": {
      "$ifNull": [{ "$arrayElemAt": ["$data.type", 0] }, null]
    }
  }}
])

Answer 2

Why you dont check in callback if result==null and create your own empty object?

let name = "form4";
db.myCollec.find({"name":name} , {"name":1, "type":1, "_id":0}, function(err, result){
    if(err) {
         // Error handling
         return;
    }
    if (result==null){
        result = {"name":name, "type":null};
    }
});