Does mongoose / mongodb have access to object references in schema during aggregate?

问题

I'm working on a query that reads from 2 different obj referentes inside my mongo database. I will use a simple example of what im looking for.

I have 3 schemas:

User = new Schema({
    places:[{type: Schema.Types.ObjectId, ref:'Place'}],
    shouts:[{type: Schema.Types.ObjectId, ref:'Shout'}]
});
Place = new Schema({
    name:String,
    description:String,
});
Shout = new Schema({
    content:String,
});

My biggest question is if mongoose or mongodb has access to objectId references when executing the aggregate method. Allow me to elaborate.

module.exports.askForShoutInPlace = function(req, res){
    var pname = new RegExp(req.params.pname, 'i'); 
    User.aggregate(
        [
           {'$match':{ 'places':{
               '$elemMatch':{'name':pname}
                }
           },
           {'$project':{ shout:'$shouts'} },
           {'$unwind':'$shouts'},
           {'$group':{_id:'$shouts'}}
        ]).exec(function(err, results){
        res.send(results);
    });

}

That usually works fine, however I'm getting an empty array once the $match operator is called, im guessing it has to do with the object references returning undefined subobjects. is there any work around this? or does this mean I have to take another route to employ populating?

thanks for all the help in advance

回答1:

there's no way to access object Referenced data during the aggregate Process, the work around I employed for my project was to add a reference to the owner in the schemas in question.

User = new Schema({
    places:[{type: Schema.Types.ObjectId, ref:'Place'}],
    shouts:[{type: Schema.Types.ObjectId, ref:'Shout'}]
});
Place = new Schema({
    owner:{type: Schema.Types.ObjectId, ref:'Place'},
    name:String,
    description:String,
});
Shout = new Schema({
    owner:{type: Schema.Types.ObjectId, ref:'Place'},
    content:String,
});

And then employed to Aggregate directly on the subdocument to obtain the unique users who own the instances of of place, this way I can obtain a shout result matching a query and a place.

Example:

module.exports.askForShoutInPlace = function(req, res){
var pname = new RegExp(req.params.pname, 'i'); 
var stringQ = new RegExp(req.paramos.qcontent, 'i');
Place.aggregate(
    [
       //find Places that match criteria
       {'$match':{'name':pname}},
       //select owner id object to result
       {'$project':{ owner:'$owner'}},
       //group those results to single array with unique ids of users
       {'$group':{_id:'$owner'}}
    ]).exec(function(err, results){
    //find user shouts that match string and belong to owners know to be owners of a place
    Shout.find({'content':stringQ}).where({'owner':{'$in':results}}).exec(function(err, shouts){
       res.send(shouts);
    });
});

}

this is just the way I found to work around my particular needs, I hope it might help somebody.

来源：https://stackoverflow.com/questions/34235382/does-mongoose-mongodb-have-access-to-object-references-in-schema-during-aggreg