Retrieve only the queried element in an object array in MongoDB collection

Suppose you have the following documents in my collection:

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Do query:

Or

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Returns matched document (Document 1), but always with ALL array items in shapes:

However, I'd like to get the document (Document 1) only with the array that contains color=red:

How can I do this?

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Best Answer-推荐答案

MongoDB 2.2's new $elemMatch projection operator provides another way to alter the returned document to contain only the first matched shapes element:

Returns:

In 2.2 you can also do this using the $ projection operator, where the $ in a projection object field name represents the index of the field's first matching array element from the query. The following returns the same results as above:

MongoDB 3.2 Update

Starting with the 3.2 release, you can use the new $filter aggregation operator to filter an array during projection, which has the benefit of including all matches, instead of just the first one.

Results: