Mongoose, populate where an ID is specific to a project reference - node.js

Question

I m trying to populate a mongoose model where I only want the returned items to be the ones that are matched with an ID.
Edit update: In the User model below, I need to first find the correct user by id, then for the task property, I need to populate it where the projectID matches req.params.ID. How can I only populate the tasks where the projectID matches the req.params.ID. I have included my full User model as well as the Task model
//User Schema
var UserSchema = new Schema({
name: {
type: String,
trim: true,
required: "First Name is Required"
},
username: {
type: String,
trim: true,
required: "Username is Required"
},
skills: {
type: String,
trim : true
},
avatar: {
type: String
},
SQLid: {
type: Number
},
userCreated: {
type: Date,
default: Date.now
},
lastUpdated: {
type: Date
},
adminTeams: [{
type: Schema.Types.ObjectId,
ref: "Team"
}],
team: [{
type: Schema.Types.ObjectId,
ref: "Team"
}],
task: [{
projectID: {
type: String
},
theTask: {
type: Schema.Types.ObjectId,
ref: "Task"
}
}]
});
//Task Schema
var TodoSchema = new Schema({
task: {
type: String
}
});
How can I only get the task populated where the projectID is equal to a specific ID. I tried
User.findById({ "_id": req.params.id }).populate({ path: 'task', match: {projectID: req.params.pID}, select: 'theTask' })
.exec(function(err, docs){
console.log("POPULATE TASKS DOCS", docs)
But this is showing that the docs is empty.

Answer 1

you can use $elemMatch ,it will give you all those docs which matches your projectId and populate your task document .
So the query would be -
var query={
task:{
$elemMatch:{
projectId: req.params.id
}
}
}
User.find(query)
.populate('theTask')
.select('theTask') // use for getting selective data from document
.exec(function(){}) //your callback fuction
Hope I answer your question.
Thanks.

Answer 2

In your task schma you have kept the type of the task type as string and in your user schema the theTask have the refrence of the task and task its Self is just a string . Thats why it is not being populated ..
So change the task schema to (Keep it simple)-
var Task= new Schema({
name :string
});
Populate need refrence Id to get the whole document