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  1. Core Server
  2. SERVER-32947

Does mongodb $lookup operator ruins default array order?

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Details

    • Bug
    • Status: Closed
    • Major - P3
    • Resolution: Done
    • 3.4.10
    • None
    • Aggregation Framework
    • None
    • ALL
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      1. Get some test docs with array field, filled with ObjectId elements.
      2. Run this query.

      db.getCollection('trades').aggregate([
      		 
      {  '$match': {
      		 
              _id: ObjectId('5a546428f228c3156579fe00')
      		 
          } 
      }, 
      { 
          '$lookup': { 
              from: 'images',
      		 
              localField: 'images',
      		 
              foreignField: '_id',
      		 
              as: 'images'
      		 
          }
      		 
      }
      		 
      ]);

      3. Default order is ruined.

      Show
      1. Get some test docs with array field, filled with ObjectId elements. 2. Run this query. db.getCollection( 'trades' ).aggregate([ { '$match' : { _id: ObjectId( '5a546428f228c3156579fe00' ) } }, { '$lookup' : { from: 'images' , localField: 'images' , foreignField: '_id' , as: 'images' } } ]); 3. Default order is ruined.

    Description

      I faced with some strange things when I was working with mongoose. I got mongodb collection with some docs:

      {
      		 
      "_id" : ObjectId("5a0bf58c9616e5016426d5ef"),
      		 
      "categoryId" : 101,
      		 
      "name" : "Some name of something",
      		 
      "price" : 50000,
      		 
      "images" : [ 
          ObjectId("5a0bf5349616e5016426d5e9"),
      		 
          ObjectId("5a0bf6ac9616e5016426d5f7")
      		 
      ],
      		 
      }

      When I join images in "images" field by ObjectId, $lookup operator jumble up default order of array. Why is this happening? When I use third-party ODM (Mongoose) to join images default order of images array is preserved.

      db.getCollection('trades').aggregate([
      		 
      {  '$match': {
      		 
              _id: ObjectId('5a546428f228c3156579fe00')
      		 
          } 
      }, 
      { 
          '$lookup': { 
              from: 'images',
      		 
              localField: 'images',
      		 
              foreignField: '_id',
      		 
              as: 'images'
      		 
          }
      		 
      }
      		 
      ]);

      Attachments

        Issue Links

          related to

          New Feature - A new feature of the product, which has yet to be developed. SERVER-7528 Order of responses to a MongoDB $in query

          • Trivial - P5 - Cosmetic problem like misspelt words or misaligned text.
          • Open

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            People

              mark.agarunov Mark Agarunov
              penpaul Pavel
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                Updated:
                Resolved: