Mongoose's populate method breaks promise chain? - express

Question

So I have a mongoose Schema that looks like this:
var Functionary = new Schema({
person: {
type: mongoose.Schema.Types.ObjectId,
ref: 'Person'
},
dateOfAssignment: Date,
dateOfDischarge: Date,
isActive: Boolean
});
var PositionSchema = new Schema({
name: String,
description: String,
maxHeadCount: Number,
minHeadCount: Number,
currentHeadCount: Number,
currentlyHolding: [Functionary],
historical: [Functionary],
responsibleTo: {
type: mongoose.Schema.Types.ObjectId,
ref: 'Position'
}
});
*note that the Position document can reference itself in the ResponsibleTo field.
Now, I'm trying to build a method that will search the Positions collection, populate the currentlyHolding[].person.name field and the responsibleTo.currentlyHolding[].person.name field, and also return the total number of records found (for paging purposes on the front-end).
Here's what my code looks like:
exports.search = function(req, res) {
var result = {
records: null,
count: 0,
currentPage: req.params.page,
totalPages: 0,
pageSize: 10,
execTime: 0
};
var startTime = new Date();
var populateQuery = [
{
path: 'currentlyHolding.person',
select: 'name'
}, {
path:'responsibleTo',
select:'name currentlyHolding.person'
}
];
Position.find(
{
$or: [
{ name: { $regex: '.*' + req.params.keyword + '.*', $options: 'i' } },
{ description: { $regex: '.*' + req.params.keyword + '.*', $options: 'i' } }
]
},
{},
{
skip: (result.currentPage - 1) * result.pageSize,
limit: result.pageSize,
sort: 'name'
})
.exec()
.populate(populateQuery)
.then(function(doc) {
result.records = doc;
});
Position.count(
{
$or: [
{ name: { $regex: '.*' + req.params.keyword + '.*', $options: 'i' } },
{ description: { $regex: '.*' + req.params.keyword + '.*', $options: 'i' } }
]
})
.exec()
.then(function(doc) {
result.count = doc;
result.totalPages = Math.ceil(result.count / result.pageSize);
})
.then(function() {
var endTime = new Date();
result.execTime = endTime - startTime;
return res.json(200, result);
});
};
My problem is when I run the first query with the populate method (as is shown), it doesn't work. I take away the populate and it works. Is it true that the populate method will break the promise? If so, are there better ways to achieve what I want?

Answer 1

It's been a while since you asked, but this might still help others so here we go:
According to the docs, .populate() doesn't return a promise. For that to happen you should chain .execPopulate().
Alternatively, you can put .populate() before .exec(). The latter will terminate the query builder interface and return a promise for you.