Hi I am trying to build a social app where user can follow each other my user schema looks like this :

{
      _id: ObjectId('62b6a1ad5bb65d5a1e2c0dcc'),
      name: 'Admin',
      username: 'Admin',
      email: '[email protected]',
      password: '$2b$10$qVWp8HZdId/cjVOXwiNLyeyv0jNo7BMFqFEKwNQniusazABp6s216',
      profilePicture: '',
      coverPicture: '',
      followers: [
        ObjectId('62b6abc96e3985aa5b2848b8'),
        ObjectId('62b6abb96e3985aa5b2848b0'),
        ObjectId('62b6abbf6e3985aa5b2848b2'),
      ],
      following: [],
      isAdmin: false,
      createdAt:  2022-06-25T05:48:29.095Z,
      updatedAt:  2022-06-25T07:45:33.290Z,
      __v: 0,
}

Post schema

{
      _id: ObjectId('62b6eaba03ca17b3eb642e24'),
      userId: ObjectId('62b6a1ad5bb65d5a1e2c0dcc'),
      description: 'one',
      image:'https://firebasestorage.googleapis.com/v0......',
      tags: [],
      likes: [],
      createdAt: '2022-06-25T11:00:10.108Z',
      updatedAt: '2022-06-25T11:00:10.108Z',
      __v: 0,
}

Followers , Following , likes are the array of objectId . I want to fetch timeline post for user it include the post of that users and post of his following . How I can achive this result without runinng loops in the nodejs server .

CodePudding user response：

use $lookup for get matched post
the result will be added to field my-post and follow-post

try playground

db.user.aggregate(
[{
    $lookup: {
        from: 'post',
        localField: '_id',
        foreignField: 'userId',
        as: 'my-post'
    }
}, {
    $lookup: {
        from: 'post',
        localField: 'followers',
        foreignField: 'userId',
        as: 'follow-post'
    }
}]
)