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What is the difference between the cursor.count() and cursor.size() methods of MongoDB's DBCursor?

Mark Amery
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Byter
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3 Answers3

32

From the Javadoc of the MongoDB Java Driver, it says :

DBCursor.count(): Counts the number of objects matching the query. This does not take limit/skip into consideration.

DBCursor.size(): Counts the number of objects matching the query. This does take limit/skip into consideration.

Mark Amery
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Parvin Gasimzade
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2

More than an answer I'd like to point out an issue that our team faced "mixing" this two.

We had something like this:

DBCursor cursor = collection.find(query).limit(batchSize);

logger.info("{} items found.", cursor.count());

while (cursor.hasNext()) {
...
}

It turned out that after calling the cursor.count() method, the limit was ignored (plase take a look at this other question) , we intended to know how many items were returned by the query so we should have called the cursor.size() method instead, since calling the count one did have an undesired collateral effect.

I hope this could be helpful to anyone else since it was not that easy to find the source of the issue we were facing.

Community
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David Chaverri
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  • Are you saying that the `cursor.count()` not only ignored the limit as documented, but actually removed the limit from the cursor, such the subsequent operations such as iterating the cursor behave as if the limit was not set? – dan carter Jun 16 '16 at 23:15
0

When I first read the documentation on the difference between cursor.count and cursor.size, I was similarly stumped b/c I didn't understand what it meant to not consider skip or limit. I found this article to be helpful read more here. I think the following example illustrates the differences

// by default cursor.count ignores limit or skip. note that 100 records were returned despite the limit being 5
> db.restaurants.find( { "cuisine": "Bakery", "address.zipcode": "10462" } ).limit(5).count();
100
// if you want to consider limits and skips, then add an optional parameter specifying so
> db.restaurants.find( { "cuisine": "Bakery", "address.zipcode": "10462" } ).limit(5).count(true);
5
// cursor.size on the other hand abides by limits and skips
> db.restaurants.find( { "cuisine": "Bakery", "address.zipcode": "10462" } ).limit(5).size();
5
forrestDinos
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