How to exclude null values from Mongoose populate query

问题

I am building an app and I have create 2 models.

  const UserSchema = new Schema({
    _id: Schema.Types.ObjectId,
    account:{
      type: String,
      unique: true
    }, 
    email: String,
    first_name: String,
    last_name: String
}

  const VenueSchema = new Schema({
    _id: Schema.Types.ObjectId,
    venue_type: String,
    capacity: Number
  })

and

const MediatorSchema = new Schema({
    _id: Schema.Types.ObjectId,
    account:{
      type: String,
      unique: true
    },
    user: {type: Schema.Types.ObjectId, 
      ref:'User'
    }
    venue: {type: Schema.Types.ObjectId, 
      ref:'Venue'
    }
  })

the mediator Schema is created in order to populate multiple paths .

The problem is that when i try to create a query like

var populateQuery = [{path:'user',match: { account:'testuser1'},select:'email'},{path:'venue',match: { venue_type: 'club'}, select:'venue_type'}];

const confirmedVenues = await  Mediator.find({})  
.exists('venue',true)
.populate(populateQuery)
.exec();

the returned array contains objects with null values when the match is not fulfilled.

For example when I query with the previous matches I get the following results

So what I want is , when a user or venue or something is NULL ( so the match is not fulfilled) , the Whole object not to be returned.

I got the following solution but i dont want to do it this way

var i =confirmedVenues.length;
while(i--){
  if(confirmedVenues[i].user == null){
    temp.splice(i,1)
  }
}

回答1:

Finally , I had to use aggregation here , there are not other option .

The schemas dont need to change

var results =await dbo.collection('mediators').aggregate([
     { $lookup:
         {
           from: 'venues',
           localField: 'venue',
           foreignField: '_id',
           as: 'venue'
         }
      },
        $match:{$and:[{"venue.venue_type":req.query.venue_type} , {"venue.capacity":{$gte:parseInt(req.query.capacitylb) , $lte:parseInt(req.query.capacityub)}}]}
      },{
        $lookup:
         {
           from: 'users',
           localField: 'user',
           foreignField: '_id',
           as: 'user'
         }
      },{
        $lookup:
        {
           from: 'professionals',
           localField: 'professional',
           foreignField: '_id',
           as: 'professional'
        }
      },{
        $lookup:
        {
          from:'availabilities',
          localField: 'availability',
          foreignField: '_id',
          as: 'availability'
        }
      },{
        $unwind: '$availability'
      },{
        $match:{$and:[{"availability.start":{$lte:new Date(req.query.dateFrom)}},{"availability.end":{$gte:new Date(req.query.dateTo)}}]}
      },{
        $lookup:
        {
          from:'locations',
          localField: 'location',
          foreignField: '_id',
          as: 'location'
        }
      },{
        $project:{
          "_id":1,
          "email":"$user.email",
          "organization_name":"$user.organization_name",
          "website":"$user.website",
          "profile_pic_hash":"$user.profile_pic_hash",
          "bio_hash":"$user.bio_hash",
          "venue_type":"$venue.venue_type",
          "capacity":"$venue.capacity",
          "flat_fee":"$professional.flat_fee",
          "per_participant_fee":"$professional.per_participant_fee",
          "hourly_fee":"$professional.hourly_fee",
          "start_date":"$availability.start",
          "end_date":"$availability.end",
          "distance":"$dist.calculated",
          "location":"$location.location.coordinates",
          "country":"$location.country",
          "city":"$location.city",
          "street":"$location.street",
          "number":"$location.number",
          "zip":"$location.zip"}}

It worked perfect for me. Thanks Anthony Winzlet for your help.

来源：https://stackoverflow.com/questions/52150132/how-to-exclude-null-values-from-mongoose-populate-query