MongoDB Aggregation Pipeline and combining deeply nested objects

Question

Let's say I have a collection of objects:

{
   _id : 1,
   list1 : [
      { name: 'This is my name', value: 'This is my value' },
      { name: 'name number 2', value: 'value number 2' }
   ],
   list2 : [
      { name: 'Another name', value: 'Another value' }
   ],
   deeper : {
      list3 : [
         { name: 'Another name but even deeper', value: 'Another value but deeper' }
      ]
   }
}

Using aggregation pipeline how would I return a single list of name/value objects? Result should be:

{
   _id : 1,
   combinedList : [
      { name: 'This is my name', value: 'This is my value' },
      { name: 'name number 2', value: 'value number 2' },
      { name: 'Another name', value: 'Another value' },
      { name: 'Another name but even deeper', value: 'Another value but deeper' }
   ]
}

PART 2:

Now, how to flatten deeply nested objects from a whole collection into a single response? Example:

{
   "_id" : 0,
   list1 : [
      { name: 'This is my name', value: 'This is my value' },
      { name: 'name number 2', value: 'value number 2' }
   ],
   list2 : [
      { name: 'Another name', value: 'Another value' }
   ]
},
{
   "_id" : 1,
   list1 : [
      { name: 'This is my name', value: 'This is my value' },
      { name: 'name number 2', value: 'value number 2' }
   ],
   deeper : {
      list2 : [
         { name: 'Another name but even deeper', value: 'Another value but deeper' }
      ]
   }
}

The result should be the same document as above (combinedList).

Barno · Accepted Answer · 2014-11-24 18:46:55Z

1

you can use aggregate and setUnion

db.coll.aggregate([
    {
        $match:{_id:1}  
    },
     { 
         $project: {_id: 0 ,
                    combinedList: { $setUnion: [ "$deeper.list3","$list2", "$list1" ] }} 
     }
   ]
)

result

{
    "result" : [ 
        {
            "combinedList" : [ 
                {
                    "name" : "Another name but even deeper",
                    "value" : "Another value but deeper"
                }, 
                {
                    "name" : "Another name",
                    "value" : "Another value"
                }, 
                {
                    "name" : "name number 2",
                    "value" : "value number 2"
                }, 
                {
                    "name" : "This is my name",
                    "value" : "This is my value"
                }
            ]
        }
    ],
    "ok" : 1
}

http://docs.mongodb.org/manual/reference/operator/aggregation/setUnion/

you have to use version 2.6.

edited Nov 24, 2014 at 18:46

answered Nov 24, 2014 at 18:41

Barno

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2 Comments

JayJohnsonDesigns Over a year ago

Thank you @Barno! Can I through one more dimension in there? What if I have a list of objects each with a list. Example: {

JayJohnsonDesigns Over a year ago

I added the example to my original question.

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