Add user id in my profile collection using aggregation - mongodb

Question

Below is my user collection data
user collection
{
"_id" : ObjectId("584bc9ba420a6b189c510af6"),
"old_user_id" :1,
"name" :"aaa"
},
{
"_id" : ObjectId("9ba420a584bc6b189c59ba42"),
"old_user_id" : 2,
"name" :"bbb"
},
{
"_id" : ObjectId("59ba4284bc0a6b189c3323w23"),
"old_user_id" : 3,
"name" :"ccc"
}
myprofile collection
{
"old_user_id" :1,
"name" :"aaa",
"number":"123456789"
},
{
"old_user_id" : 2,
"name" :"bbb",
"number":"678912345"
},
{
"old_user_id" : 3,
"name" :"ccc",
"number":"673458912"
},
{
"old_user_id" : 2,
"name" : "bbb",
"adress" : "afsfdidhddk"
}
My expectation:
I need to match old_user_id in both collections and update the user collection '_id' in my profile collection
{
"userid":"584bc9ba420a6b189c510af6",
"old_user_id" :1,
"name" :"aaa",
"number":"123456789"
},
{
"userid":"9ba420a584bc6b189c59ba42",
"old_user_id" : 2,
"name" :"bbb",
"number":"678912345"
},
{
"userid":"59ba4284bc0a6b189c3323w23",
"old_user_id" : 3,
"name" :"ccc",
"number":"673458912"
},
{
"old_user_id" : 2,
"name" : "bbb",
"adress" : "afsfdidhddk"
"userid" : "9ba420a584bc6b189c59ba42"
}

Answer 1

You can use mongo aggregation. Use of $lookup, $project and $unwind will help.
I have formulated the query, hope this helps:
db.myprofile.aggregate([
{
$lookup:
{
from: "user",
localField: "old_user_id",
foreignField: "old_user_id",
as: "inventory_docs"
}
},
{ $project : { _id : "$inventory_docs._id",
old_user_id:"$old_user_id",
"name":"$name",
"number":"$number" } },
{$unwind: "$_id"}
])

Answer 2

Update:
db.user.find().forEach(function (user) {
var cursor = db.myprofile.find({"old_user_id": user.old_user_id});
cursor.forEach(function(myprofile) {
myprofile.userid = user._id.str;
db.myprofile.save(myprofile);
});
});
Result:
db.myprofile.find().pretty()
{
"_id" : ObjectId("584e7294678ae15db4fab039"),
"old_user_id" : 1,
"name" : "aaa",
"number" : "123456789",
"userid" : "584e7294678ae15db4fab035"
}
{
"_id" : ObjectId("584e7294678ae15db4fab03a"),
"old_user_id" : 2,
"name" : "bbb",
"number" : "678912345",
"userid" : "584e7294678ae15db4fab036"
}
{
"_id" : ObjectId("584e7294678ae15db4fab03b"),
"old_user_id" : 3,
"name" : "ccc",
"number" : "673458912",
"userid" : "584e7294678ae15db4fab037"
}
{
"_id" : ObjectId("584e7294678ae15db4fab03c"),
"old_user_id" : 2,
"name" : "bbb",
"adress" : "afsfdidhddk",
"userid" : "584e7294678ae15db4fab036"
}
Note: the _id fiels still appears in the resulting documents, but you should be able to live with that. Is a default behaviour of MongoDB. You can create a collection with no indexed _id field like in here: db.createCollection("user", { autoIndexId: false })