如果存在与 MongoDB 和 Mongoose 匹配的另一个文档，则添加字段

Question

I have in my DB a collection of Posts with basic informations like:

Posts = {
   _id: '',
   title '',
   desc '',
...
}

i also have a Likes collection like (document are created or deleted of user like the post):

Likes = {
_id: '',
user_id: '',
post_id: '',
}

and the goal would be that when i get a list of Posts , to add a field Liked who show true/false if a document Like match or not, and also the number of match in the Like collection (this i know how to) like:

Posts = [{
   _id: '',
   title '',
   desc '',
   liked: true,
   likes: 5,
...
}, ...]

i've used $lookup & $addFields but can join only with one value so far. In my case i want one specific document and filtered by 2 fields (user_id, post_id).

What i get so far:

    const posts = await posts.aggregate
    ([
      {
        $lookup: {
          from: 'likes',
          localField: '_id',
          foreignField: 'post_id',
          as: 'likes'
        }
      },
      { $match: {
        user_id: mongoose.Types.ObjectId(req.params.id),
      } },
      {
        $addFields: {
          likes: 
            { $size: "$likes" } // here nb of likes
        }
      }
    ])

Answer 1

Try with this one

db.getCollection('post').aggregate([
  {
    $lookup: {
      from: 'likes',
      localField: '_id',
      foreignField: 'post_id',
      as: 'likes'
    }
  },
  {
      $addFields:{
          size:{$size:"$likes"},
          liked: 
          {$size: {
                        $filter: {
                            input: "$likes",
                            as: "item",
                            cond: { $eq: [ "$$item.user_id", ObjectId("5f2a38ad61a591cf96d58f6a") ] }
                        }
                }
             }
          }
  },
  {
  $addFields:{
      liked:{
          $cond:[{$eq:["$liked",0]},false,true]
          }
      }    
  }
])