I have two collections. One to store all the user Details and another to store movies. I have a user_id field which has the objectId of the user who uploads it in the movie collection. Now I need to store all the movie ObjectId's as a array in the corresponding user collection. Like one to many relationship. say, I have some movie documents :

     [{
          'id' : '1',
          'title' : 'Pk',
          'user_id' : '25'
      },
     {
          'id' : '2',
          'title' : 'Master',
          'user_id' : '25'
     }]

In user collection, I want to store all the Movie_id's as a array to the corresponding user.

      { 
         'user_id' : '25',
         'user_name' : 'john',
          'Movie_ids' : ['1','2']
      }

How can I achieve this using mongodb and express.js?

CodePudding user response：

Ok, I'm not sure if this is entirely what you are looking for but you can use javascript function .filter on the movie object to get all the movies with user_id=25 and then map the id's of those movies to a new array like this:

let movies = [
  {
    "id": "1",
    "name": "pk",
    "user_id": "25"
},{
    "id": "2",
    "name": "Master",
    "user_id": "25"
}]
let user = {
  "id": "25",
  "name": "john"
}

let sortedMovies = movies.filter(movie => movie.user_id  === user.id).map(movie => movie.id);
user.movieIDs = sortedMovies;

A link to test the code: https://playcode.io/816962/

CodePudding user response：

Query

• $lookup does what you want (see mongodb documentation is very good)
• $map is used to keep only the ids in the array

Test code here

db.users.aggregate([
  {
    "$lookup": {
      "from": "movies",
      "localField": "user_id",
      "foreignField": "user_id",
      "as": "movies"
    }
  },
  {
    "$set": {
      "movies": {
        "$map": {
          "input": "$movies",
          "in": "$$this.id"
        }
      }
    }
  }
])