How to change data type of a field in mongo

Following query helps you convert the data type of a field from

• string to integer:

db.my_collection.find().forEach( function(obj) {
    obj.field-name= parseInt(obj.field-name);
    db.my_collection.save(obj);

});

• and from integer to string : 

db.my_collection.find().forEach( function(obj) {
    obj.field-name= ""+obj.field-name;
    db.my_collection.save(obj);

});