Mongodb Query To select records having a given key

Question

The records in my database are

{\"_id\":\"1\",\"fn\":\"sagar\",\"ln\":\"Varpe\"}

{\"_id\":\"1\",\"fn\":\"sag\",\"score\":\"10\"}

{\"_id\":\"1\",\"ln\":\"ln         


        

Answer 1

db.collection.find({ ln: { $exists: true} });

The $size operator matches any array with the number of elements specified by the argument. For example:

db.collection.find({ ln: { $exists: true, $size: 0 } });

$size does not accept ranges of values. To select documents based on fields with different numbers of elements, create a counter field that you increment when you add elements to a field.