mongoose query to merge array of objects

Question

I have a collection like this:

collection base:

{
    _id:"a"
    field:[
        {
          _id:"aa",
          field1:"aa1"
        },
        {
          _id:"ab",
          field2:"ab2"
        },
    ]
}

what query can I use to have a result like this:

{
    _id:"a"
    field:            
        {
          _id:"ab",
          field2:"ab2",
          field1:"aa1"
        },        
}

In other words i want use this function as mongoose query on field array:

field.reduce((p,c)=>({...p,...c}),{})

on what base you want to select _id:"ab" why its not _id:"aa"? — turivishal
– turivishal, Commented Apr 11, 2021 at 5:53
i want to merge array items from start to end into one object — mehdi parastar
– mehdi parastar, Commented Apr 11, 2021 at 5:55

turivishal · Accepted Answer · 2021-04-11 05:56:31Z

1

$reduce to iterate loop of field, set initialValue to empty object,
$mergeObjects to merge initialValue means $$value and $$this means current object

db.collection.aggregate([
  {
    $addFields: {
      field: {
        $reduce: {
          input: "$field",
          initialValue: {},
          in: { $mergeObjects: ["$$value", "$$this"] }
        }
      }
    }
  }
])

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answered Apr 11, 2021 at 5:56

turivishal

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