how to find in mongo using object id references using nodejs?

Question

i have two schemas

var UserSchema  =new mongoose.Schema({
    username:String,
    password:String,
    user_email:String,
    user_contacts:[
        {
            type:mongoose.Schema.Types.ObjectId,
            ref:"User"
        }
    ]
})
module.exports=mongoose.model("User",UserSchema);

and

var friendRequestSchema=new mongoose.Schema({
    requester:{
        type:mongoose.Schema.Types.ObjectId,
        ref:"User"
    },
    recipient:{
        type:mongoose.Schema.Types.ObjectId,
        ref:"User"
    },
    //1 for requested , 2 for accepted , 3 for rejected
    status:Number
});
module.exports=mongoose.model("FriendRequest",friendRequestSchema);

and i want to find all friend requests with specific user id for requester field ,then i want to get all recipient users of these requests, and finally adding them to a dictionary where the key is the recipient user and the value is the friendRequest associated with it so i can pass it to a ejs file like this:

res.render("myrequests",{myDictionary:myDictionary});

Your question is off to a good start, but now you need to continue with "here's what I tried..." "Here's what I was expecting...", "Here's what actually happened..." It's worthwhile asking your actual question in the body of your question as opposed to just in the title, too. — Wyck
– Wyck, Commented Feb 20, 2019 at 3:42

Vivek Ghanchi · Accepted Answer · 2019-11-01 10:39:35Z

2

you can now do it in Mongo 3.2 using $lookup

$lookup takes four arguments

from: Specifies the collection in the same database to perform the join with. The from collection cannot be sharded.

localField: Specifies the field from the documents input to the $lookup stage. $lookup performs an equality match on the localField to the foreignField from the documents of the from collection.

foreignField: Specifies the field from the documents in the from collection.

as: Specifies the name of the new array field to add to the input documents. The new array field contains the matching documents from the from collection.

db.Foo.aggregate(
  {$unwind: "$bars"},
  {$lookup: {
    from:"bar",
    localField: "bars",
    foreignField: "_id",
    as: "bar"

   }},
   {$match: {
    "bar.testprop": true
   }}
)

Hope this will solve your problem!!!

edited Nov 1, 2019 at 10:39

answered Feb 20, 2019 at 5:23

Vivek Ghanchi

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