C# mongodb driver 2.2.3 how to set batchSize for cursor

Question

I am using official C# driver for MongoDB 2.2.3

How can I set batch size for the cursor using the C# driver?

With javascript I can create a cursor and set batch size for it:

var cursor = db.statistics.find(query).batchSize(100)

and I can iterate through all items using the following statement:

while(cursor.objsLeftInBatch()>0){
    var doc = cursor.next();
    //process doc
}

I would like to have the same behaviour in C# with async/await support. I know that I can use cursor from C# but it's default batch size is 4MB. This is too match to return to the client with one call.

Answer 1

You can set the batch size in the FindOptions parameter of FindAsync.

Here's the basic pattern to explicitly handle the batches:

var filter = new BsonDocument();
var options = new FindOptions<BsonDocument>
{
    // Get 100 docs at a time
    BatchSize = 100
};

using (var cursor = await test.FindAsync(filter, options))
{
    // Move to the next batch of docs
    while (await cursor.MoveNextAsync())
    {
        var batch = cursor.Current;
        foreach (var doc in batch)
        {
            // process doc
        }
    }
}

But you can also call ForEachAsync on the cursor and the batches will be transparently fetched on demand:

using (var cursor = await test.FindAsync(filter, options))
{
    await cursor.ForEachAsync(doc =>
    {
        // process doc
    });
}