How to get the length of a cursor from mongodb using python?

Question

I'm looking for a feasible way to get the length of cursor got from MongoDB.

Answer 1

It's actually as simple as

len(list(cursor))

Note that it will however consume the cursor.

Answer 2

The cursor.count method is deprecated since pymongo 3.7.

The recommended method is to use the count_documents method of the collection.

Answer 3

cursor.count()

Counts the number of documents referenced by a cursor. Append the count() method to a find() query to return the number of matching documents. The operation does not perform the query but instead counts the results that would be returned by the query.

db.collection.find(<query>).count()

https://docs.mongodb.com/manual/reference/method/db.collection.count/

Answer 4

The variant of the previous answer:

len(list(cursor.clone()))

doesn't consume cursor

Answer 5

According to the pymongo documentation, a Pymongo cursor, has a count method:

count(with_limit_and_skip=False)

By default this method returns the total length of the cursor, for example:

cursor.count()

If you call this method with with_limit_and_skip=True, the returned value takes limit and skip queries into account. For example, the following query will return 5 (assuming you have more than 5 documents):

cursor.limit(5).count(True)

Answer 6

For some reason, some aggregations return an object that doesn't have the same methods, maybe different class, simple solution, convert the pseudo cursor to an array:

// A simple aggregation with `group`
var cursor = db.getCollection('collection').aggregate([
    {$match: {
        "property": {"$exists": true }
    }},
    {$group: { 
        _id: '$groupable',
        count: {$sum: 1}
    }},
    {$sort: {
        count: -1
    }}
]);

// Converting the "cursor" into an array
var cursor_array = cursor.toArray();

// Looping as an array using `for` instead of `while`
for (var i = 0; i < cursor_array.length; i++) {
    print(cursor_array[i]._id+'\t'+cursor_array[i].count);
}

Notice this solution is only for the shell, I don't know if this array method exists in other libraries.

Answer 7

I find that using cursor.iter().count() is a feasible way to resolve this problem

Answer 8

I was able to do count it this way:

def count():
    collection = db[col_name]
    count = collection.count_documents({"visited" : True})
    
    return count

Answer 9

len(list(cursor.clone())) worked really well for me, does not consume the editor so it can be use straight with your variable