mongodb, copy all documents to collection

collection_A is mapReduced result.

If I want to save { '11-8-12' : collection_A} in collection_B.

How can I save one 开发者_如何转开发collection to another collection, as one of elements?

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I don't think you can directly do that.

You have to manually build the document and save it to the database.

You can write this in JS and execute it with db.eval(...) so that data won't be transferred to the client, but this will convert integers to floats (the same problem you have with the mongodb shell).