Retrieving an embedded object as a document via the aggregation framework in MongoDB

Question

If I have a document, which contains an embedded object as a value of one of its fields, like this:

{ _id: ObjectId("..."), embeddedObject: { k1: "val1", k2: "val2", k3: "val3" } }

then how can I retrieve the embedded object itself as an output document with aggregation framework (pipeline operators)? Or it's not possible?

I.e., I need finally to get just the following result:

{ k1: "val1", k2: "val2", k3: "val3" }

Although operators $project, $match, $unwind, $group solve the close issues, none of them seems to be able to help precisely with my aforementioned request.

Yathish Manjunath · Accepted Answer · 2017-10-12 08:45:18Z

2

This can be achieved using one the aggregation pipeline operator $replaceRoot

  db.[collection].aggregate( [
       {
         $replaceRoot: { newRoot: "$embeddedObject" }
       }
    ] );

This will result in below output :

{ k1: "val1", k2: "val2", k3: "val3" }

answered Oct 12, 2017 at 8:45

Yathish Manjunath

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1 Comment

Alexander Shevkunenko Over a year ago

Superb. Helped. Exactly what I needed. Thanks for a prompt reply!

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