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  1. Core Server
  2. SERVER-18794

Add an aggregation expression to convert an object to an array of key, value pairs

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    • Fully Compatible
    • v3.4
    • Query 2017-03-06

    Description

      In many cases, it would be useful to convert an object to an array. We should add an aggregation expression to do so. For example, it could be called $objectToArray, and do something like this:

      > db.foo.insert({_id: 0, subDoc: {a: 1, b: 3, c: "example"}});
      		 
      > db.foo.aggregate([{$project: {expanded: {$objectToArray: "$subDoc"}}}])
      		 
      {_id: 0, expanded: [{k: "a", v: 1}, {k: "b", v: 3}, {k: "c", v: "example"}]}

      Original Description

      Currently, if a collection contains the following document: 

      {_id: 0, data: {a: 1, b: 2, c: 3}}

      There is no way to unwind that one document into the following three documents:

      {_id: 0, data: {a: 1}}
      		 
      {_id: 0, data: {b: 2}}
      		 
      {_id: 0, data: {c: 3}}

      One way to accomplish this would be to add a stage to unwind documents, e.g.

      db.coll.aggregate([{$objectToArray: {field: '$data'}}])

      Which would yield the following document, which could then be unwound to produce the desired result:

      {_id: 0, data: [{a: 1}, {b: 2}, {c: 3}]}

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          is depended on by

          New Feature - A new feature of the product, which has yet to be developed. CSHARP-1939 Add an aggregation expression to convert an object to an array of key, value pairs

          • Major - P3 - Major loss of function.
          • Backlog
          is duplicated by

          New Feature - A new feature of the product, which has yet to be developed. SERVER-5947 Add ability to project key names as values and values as key names

          • Major - P3 - Major loss of function.
          • Closed

          New Feature - A new feature of the product, which has yet to be developed. SERVER-11392 $unwind on subdocuments

          • Major - P3 - Major loss of function.
          • Closed
          is related to

          New Feature - A new feature of the product, which has yet to be developed. SERVER-23310 Add an expression to convert an array of pairs to an object

          • Major - P3 - Major loss of function.
          • Closed

          Improvement - An improvement or enhancement to an existing feature or task. SERVER-2507 variable field name in queries

          • Minor - P4 - Minor loss of function, or other problem where easy workaround is present.
          • Backlog
          related to

          Bug - A problem which impairs or prevents the functions of the product. DOCS-10459 The documentation for $objectToArray and $arrayToObject is missing

          • Major - P3 - Major loss of function.
          • Closed

          New Feature - A new feature of the product, which has yet to be developed. DRIVERS-358 Aggregation Framework Support for 3.6

          • Major - P3 - Major loss of function.
          • Closed

          New Feature - A new feature of the product, which has yet to be developed. SERVER-27774 Add $of for iterating over object keys

          • Major - P3 - Major loss of function.
          • Closed
          links to

          Web Link Pull Request

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              tess.avitabile@mongodb.com Tess Avitabile (Inactive)
              lch1990710 Lee Chi Hang
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                Updated:
                Resolved: