Populate on basis of condition in mongoose, mongoDB

Question

Here is my code to get one floorplan and populate all flats linked with this

see the code below :

var floorplan = Floorplan.find({      project: req.params.project,      tower: req.params.tower,      isDeleted: false  }); floorplan.populate('flats').exec(function(err, floorplan) {     if (err) { return res.send(err); }     if (!floorplan) { return res.status(401).json(); }     res.status(200).json(floorplan); }); 

But I want to populate only those flats where isDeleted : false How to achive this ??

Schema of floorplan

var FloorplanSchema = new Schema({     project: { type: Schema.ObjectId, ref: "Project" },     flats: [{ type: Schema.ObjectId, ref: "Flat" }],     tower: [{ type: Schema.ObjectId, ref: "Tower" }],     unitType: String,     area: Number,     floorPlan2D: String,     floorPlan3D: String,     livingRoomArea: Number,     kitchenArea: Number,     balconies: Number,     bathRooms: Number,     isDeleted: { type: Boolean, 'default': false },     createdAt: { type: Date, 'default': Date.now } }); 

Schema of flat

var FlatSchema = new Schema({     tower: { type: Schema.ObjectId, ref: "Tower" },     floorplan: { type: Schema.ObjectId, ref: "Floorplan" },     project: { type: Schema.ObjectId, ref: "Project" },     status: String,     floor: Number,     size: String,      superbuiltup_area: Number,      directionFacing: String,     furnishingState: String,     flooringType: String,     createdAt: { type: Date, 'default': Date.now },     isDeleted: { type: Boolean, 'default': false },  }); 

Answer 1

The populate() method has an option which allows for filtering, you can either try this

Floorplan .find({      project: req.params.project,      tower: req.params.tower,      isDeleted: false  }) .populate({     path: 'flats',     match: { isDeleted: false } }) .exec(function(err, floorplan) {     if (err) { return res.send(err); }     if (!floorplan) { return res.status(401).json(); }     res.status(200).json(floorplan); }); 

or

Floorplan .find({      project: req.params.project,      tower: req.params.tower,      isDeleted: false  }) .populate('flats', null, { isDeleted: false }) .exec(function(err, floorplan) {     if (err) { return res.send(err); }     if (!floorplan) { return res.status(401).json(); }     res.status(200).json(floorplan); });