Group documents by common field and bucket by month

[Alexander_Miller]

I would like to group documents based on a reference field (profileID), and then group posts for each month of the past year into an array of documents. Here is the current schema:

[
  {
    profileId: 123,
    datePosted: '2022-01-01',
    content: 'this is post content'
  },
  {
    profileId: 123,
    datePosted: '2022-01-09',
    content: 'this is a different posts content'
  },
  {
    profileId: 456,
    datePosted: '2022-02-03',
    content: 'this is some other posts content'
  },
]

Here is the desired schema:

[
  {
    profileId: 123,
    postsByMonth: [
      {
        month: '2022-01-01',
        posts: [
          {
            datePosted: '2022-01-01',
            content: 'this is post content'
          },
          {
            datePosted: '2022-01-09',
            content: 'this is a different posts content'
          },
        ]
      },
    ]
  }, 
  {
    profileId: 456,
    postsByMonth: [
      {
        month: '2022-02-01',
        posts: [
          {
            datePosted: '2022-02-03',
            content: 'this is some other posts content'
          }
        ]
      }
    ]
  }
]

What is the best way to accomplish this using aggregation? Thank you in advance!!

[Asya_Kamsky]

Best would be two $group stages, first one groups by profileId and month of datePosted, and then the second groups by profileId pushing posts into an array…

Asya

[Alexander_Miller]

Thank you! Grouping by two fields during the first stage was just what I needed.