I have saved the below query as med.js
var cust = db.Collection.find({"email":null});
var count = 0;
print("total entries: ",cust.length()," ",cust.hasNext());
while(cust.hasNext()){
nextCust = cust.next();
db.Collection.update({_id:nextCust._id},{$set : {"email":""}});
count++;
}
print("total updated: ",count);
When I am executing this Query as
mongo dbName --port 13017 ~/Documents/med.js
output is
total entries: 491502 false
total updated: 0
How come total entries are showing as 491502 but hasNext() is false. its not going in the while loop
The cursor.length() function exhausts the cursor by converting it into an array. Check the function code.
>cur.length
function (){
return this.toArray().length;
}
Hence you're getting false.
To get the count without exhausting the cursor, use cursor.count()
There are three different methods you can use in this context.
cursor.count() Modifies the cursor to return the number of documents in the result set rather than the documents themselves.
cursor.itcount() Computes the total number of documents in the cursor client-side by fetching and iterating the result set.
cursor.size() Returns a count of the documents in the cursor after applying skip() and limit() methods.
cursor.length is not a recommended approach.