Limit no. of rows in mongodb input

问题

How to limit the no. of rows retrieved in mongodb input transformation used in kettle.

I tried in mongodb input query with below queries but none of them are working :

{"$query" : {"$limit" : 10}} or {"$limit" : 10}

Please let me know where i am going wrong.

Thanks, Deepthi

回答1:

There are several query modification operators you can use. Their names are not totally intuitive and don't match the names of functions you would use in the Mongo shell, but they do the same sorts of things.

In your case, you need the $maxScan operator. You could write your query as:

{"$query": {...}, "$maxScan": 10}

回答2:

We have to use aggregation method providing by MongoDB, and here is the link: docs.mongodb.org/manual/applications/aggregation.

In my case, I use this query in MongoDB Input of Kettle, and we also have to choose Query is aggregation pipline.

{$match: {activity_type: " view "}},
{$sort: {activity_target: -1 } },
{$limit: 10}

The following screen shots can help you understand the operations more clear.

来源：https://stackoverflow.com/questions/17272198/limit-no-of-rows-in-mongodb-input