CODEWITHSUNDEEP
mongodbnosql
user3308059
user3308059

Reputation: 21

MongoDB Inner Join?

I have got two collections in MongoDB:

User collection:

{
  id : 1,
  name : "John",
  username : "Ricky1",
}

Post collection:

{
 id : 1,
 title : "mongodb collections",
 userİd : 1,
}

How do I merge these two collections?

Upvotes: 1

Views: 2466

Answers (3)

Amol
Amol

Reputation: 115

Here Example Inner Join

db.users.aggregate({ $lookup: {
from : "courses", 
localField: "courseId", 
foreignField: "_id",
 as : "usersInCourse"}}
,{ $match : { "usersInCourse" : { $ne : []}}})

Above MongoDB Query Output

{
  _id: ObjectId("643404232a8430b9d86ec42b"),
  name: 'Ishan',
  isVerified: true,
  courseId: [
    ObjectId("643402ebae34b1cbab3bb377")
  ],
  usersInCourse: [
    {
      _id: ObjectId("643402ebae34b1cbab3bb377"),
      CourseName: 'MongoDB Basics',
      price: 50
    }
  ]
},{
  _id: ObjectId("643404232a8430b9d86ec42c"),
  name: 'Bhavesh',
  isVerified: true,
  courseId: [
    ObjectId("643402ebae34b1cbab3bb377"),
    ObjectId("643402ebae34b1cbab3bb378")
  ],
  usersInCourse: [
    {
      _id: ObjectId("643402ebae34b1cbab3bb377"),
      CourseName: 'MongoDB Basics',
      price: 50
    },
    {
      _id: ObjectId("643402ebae34b1cbab3bb378"),
      CourseName: 'NodeJS',
      price: 50
    }
  ]
}

In users collection data

{
  _id: ObjectId("643404232a8430b9d86ec42b"),
  name: 'Ishan',
  isVerified: true,
  courseId: [
    ObjectId("643402ebae34b1cbab3bb377")
  ]
},
{
  _id: ObjectId("643404232a8430b9d86ec42c"),
  name: 'Bhavesh',
  isVerified: true,
  courseId: [
    ObjectId("643402ebae34b1cbab3bb377"),
    ObjectId("643402ebae34b1cbab3bb378")
  ]
},
{
  _id: ObjectId("64340835ae34b1cbab3bb38c"),
  name: 'Amol',
  isVerified: true,
  courseId: []
}

In courses collection data

{
  _id: ObjectId("643402ebae34b1cbab3bb378"),
  CourseName: 'NodeJS',
  price: 50
},
{
  _id: ObjectId("643402ebae34b1cbab3bb377"),
  CourseName: 'MongoDB Basics',
  price: 50
}

Upvotes: 0

Peter Perháč
Peter Perháč

Reputation: 20782

for all posts by username "Ricky1":

db.post.find({userId:db.user.findOne({"username" : "Ricky1"}).id});

Maybe helps a little. The mongo way to do this, though, I gather, would be to have collections of posts nested inside each user in your users collection.

Upvotes: 0

jfhernandeze
jfhernandeze

Reputation: 19

I don't think it can be done. You will need to do 2 queries:

One to find the user, and another to get all posts filtering by that userId.

Upvotes: 2

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