Want from one collection based on another collection document array element-CodePudding

I am stuck and need help to get data from another collection based array element from another collection.

My collections are as --

programs.dbs -- 
{
 "_id": ObjectId("61c8f42ec63e700b415b4bed"),
"name": "Java",
"description": "this is a dummy information",
"instructor": ["61c8f6d7e690fc413a075e15", "61c8f6d7e690fc413a071e15", "61c8f0d7e690fc413a071e15"]
}

instructor.dbs --
{
 "_id": ObjectId("61c8f6d7e690fc413a075e15"),
"name": "Instrctor1",
"description": "this is a dummy Instructor",
},

{
 "_id": ObjectId("61c8f6d7e690fc413a071e15"),
"name": "Instrctor2",
"description": "this is a dummy Instructor",
},

{
 "_id": ObjectId("61c8f0d7e690fc413a071e15"),
"name": "Instrctor3",
"description": "this is a dummy Instructor",
}

My query is to find one instructor information based on collection A instructor Array element. I have tried to use this query but getting empty result -

    db.getCollection('programs.dbs').aggregate([{$lookup:{from:'instructor.dbs',localField:'instructor',foreignField:"_id",as:'instructors'}}])

Immediate help will be great.

CodePudding user response：

if you are using mongoose maybe the populate method can work.

CodePudding user response：

Your array of instructors should not reference the IDs as strings but as ObjectId(...)

So you would need to have:

"instructor": [ObjectId("61c8f6d7e690fc413a075e15"), ObjectId("61c8f6d7e690fc413a071e15"), ObjectId("61c8f0d7e690fc413a071e15")]