title: How to select specific field in nested populate in mogoose
body: <p>here is my schema:</p>
  
  <pre><code>var UserSchema = new Schema({
      email: String,
      name: String,
      city: String,
      username: String,
      profilePic: String,
      phoneNo: Number,
      shortList: {
          project: [{ type: Schema.ObjectId, ref: "Project" }],
          flat: [{ type: Schema.ObjectId, ref: "Flat" }],
      },
  
  });
  
  var FlatSchema = new Schema({
      project: { type: Schema.ObjectId, ref: "Project" },
      status: String,
      floor: Number,
      size: String,
      type: String,
      flat_number: String,
      price: Number,
      flooringType: String,
      createdAt: { type: Date, 'default': Date.now },
      isDeleted: { type: Boolean, 'default': false },
     });
  
  var ProjectSchema = new Schema({
      name: String,
      shortName: String, 
      developer: { type: Schema.ObjectId, ref: "Developer" },
      address: {
          street_address: String,
          city: String,
          state: String,
          pin: Number,
          position: {
              lat: Number,
              long: Number
          }
      },
      ofcAddress: {
          street_address: String,
          city: String,
          state: String,
          pin: Number,
      },
  
      overview: {
          size: String,
          area: String,
          configuration: String,
          possession_starts: Date,
          info: String,
          aminities: [{ type: Schema.ObjectId, ref: "Amenity" }]
      },
      images: {
          hdpi: String,
          xhdpi: String,
          web: String,
          mdpi: String
      },
  
  });
  </code></pre>
  
  <p>here <strong>user</strong> link with <strong>flat</strong> model <strong>shortList.flat</strong> and <strong>flat</strong> model is link with the <strong>project</strong></p>
  
  <p>now i am trying to select all details as follow:</p>
  
  <pre><code>User.findById(req.params.id)
          .populate('shortList.project', { 'CalculationsRules': 0, 'KBFlatTypeCharges': 0, 'CategoryPremia': 0, 'Floor': 0, 'KBUnitType': 0, 'floorplans': 0, 'flats': 0, 'towers': 0, 'galaryImages': 0 })
          .populate('shortList.flat', { 'pricedetails': 0 })
          .exec((err, user) =&gt; {
              if (err) { return handleError(res, err); }
              if (!user) { return res.json(401); }
  //here i want to select specific field from project model
              User.populate(user, { path: 'shortList.flat.project', model: 'Project' },  (err, user) =&gt; {
                  res.status(200).json(user);
              })
          });
  </code></pre>
  
  <p>its working fine but i want to select some specific  fields form project model like name and images</p>