MongoDB - Get data in date sections from an array

Question

I am new to MongoDB, I want to get data in sections from the array.

{
   "name":"User name",
   "messages":[
      {
         "message":"Message 1",
         "date":"2022-05-12T00:00:00.000Z"
      },
      {
         "message":"Message 2",
         "date":"2022-05-12T00:00:00.000Z"
      },
      {
         "message":"Message 3",
         "date":"2022-05-13T00:00:00.000Z"
      },
      {
         "message":"Message 4",
         "date":"2022-05-13T00:00:00.000Z"
      },
      {
         "message":"Message 5",
         "date":"2022-05-13T00:00:00.000Z"
      }
   ]
}

The results I want are

[
   {
      "date":"2022-05-12T00:00:00.000Z",
      "messages":[
         {
            "message":"Message 1",
            "date":"2022-05-12T00:00:00.000Z"
         },
         {
            "message":"Message 2",
            "date":"2022-05-12T00:00:00.000Z"
         }
      ]
   },
   {
      "date":"2022-05-13T00:00:00.000Z",
      "messages":[
         {
            "message":"Message 3",
            "date":"2022-05-13T00:00:00.000Z"
         },
         {
            "message":"Message 4",
            "date":"2022-05-13T00:00:00.000Z"
         },
         {
            "message":"Message 5",
            "date":"2022-05-13T00:00:00.000Z"
         }
      ]
   }
]

I'm not familiar with MongoDB aggregation, I have looked at many questions on stack overflow but didn't find any that helped me.

Is this possible to do? If yes any help would be greatly appreciated. :)

Hi Najam, I had problem like your question how you solve retrieve data by date inside of array element.? — Min Thein Win
– Min Thein Win, Commented Dec 27, 2022 at 16:05

Usama Hasan · Accepted Answer · 2022-05-20 05:54:00Z

1

You can use aggregation to get your desired output.

db.collection.aggregate([
  {
    $unwind: "$messages"
  },
  {
    $group: {
      _id: "$messages.date",
      messages: {
        $push: "$messages"
      }
    }
  },
  {
    $project: {
      _id: 0,
      date: "$_id",
      messages: 1
    }
  }
])

answered May 20, 2022 at 5:54

Usama Hasan

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Comments

Yong Shun · Accepted Answer · 2022-05-20 09:32:15Z

1

$unwind - Deconstruct messages array to multiple documents.
$group - Group by messages.date and add messages document into messages array.
$project - Decorate output documents.

db.collection.aggregate([
  {
    $unwind: "$messages"
  },
  {
    $group: {
      _id: "$messages.date",
      messages: {
        $push: "$messages"
      }
    }
  },
  {
    $project: {
      _id: 0,
      date: "$_id",
      messages: 1
    }
  }
])

Sample Mongo Playground

edited May 20, 2022 at 9:32

answered May 16, 2022 at 7:03

Yong Shun

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1 Comment

Yong Shun Over a year ago

Corrected should be date: "$_id" not date: "$_id.date". Sorry for the typo.

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