1

Please help me to find out a suitable solution

collection were users details are stored app_users

{
  _id: {
    $oid: "abcd1235a6ad4a56dadasd"
  },
  user_name: "vikas Kandari",
  user_dp: "ASDAD486412.jpg"
}

collection where users bookings are stored bookings

{
  _id : {
    $oid : "asdasdasdasdasd"
  },
  user_id : "abcd1235a6ad4a56dadasd",
  booking_item : "some product",
  booking_date : "datetime"
}

Lookup(left Join) query i am using is 

const MongoClient = require('mongodb').MongoClient;
const assert = require('assert');
const url = 'mongodb://root:root@localhost:3000/app';
const dbName = 'app';
MongoClient.connect(url, function(err, client) {
  assert.equal(err, null);
  console.log("Connected successfully to server");
  const db = client.db(dbName);
  const collection = db.collection('users');
  collection.aggregate([{
    $lookup: {
      from: 'bookings',
      localField: '_id',
      foreignField: 'user_id',
      as: 'bookings'
    }
  }]).toArray(function(err, docs) {
    assert.equal(err, null);
    console.log(docs);
  });
  client.close();
});

I want to select bookings with there corresponding user details from users collections but Its returning blank because mongodb is comparing string with objectId so is there any way to perform this task ?

Vikas Kandari
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1 Answers1

0

Add This before the lookup

$project:{
    $let:
        {
         vars: { id:'_id.$oid' },
         in: ObjectId("$$id")
         }
}

Change to 

$lookup: {
  from: 'bookings',
  localField: '_id.$oid',
  foreignField: 'user_id',
  as: 'bookings'
}
deepak thomas
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  • 23