can we use $embed for array of array field?

[samseralam]

@JKHeadley would like to use $embed for getting inner array field data.
my schema is like this...
facilitiesPerFloor: [{
suiteInfo: {
floorNo: {
type: Types.Number
}
},
facilities: [{
type: Types.ObjectId,
ref: "facility"
}]
}]

Holding Data
"facilitiesPerFloor": [
{
"_id": "5996d930daec05116aed9e35",
"facilities": [
"5996d83a0c2b83113cdfd40c",
"5996d83a0c2b83113cdfd41c"
],
"suiteInfo": {
"floorNo": 1
}
}
]

Note: facilitiesPerFloor contains facilities array where multiple facility can be. Now how i can use $embed for getting/populating second level of facilities data.

Thanks.

[JKHeadley]

You cannot directly use $embed here to populate the facilities. You can however set up a dummy association and process your own $embed query using a post middleware function. Below is one example of how to implement this. It is by no means the most efficient solution and I can't guarantee its complete functionality but I had some success with it.

NOTE: the below code will only work for rest-hapi v0.19 and higher

'use strict';

const Q = require('q');
const _ = require('lodash');
const RestHapi = require('rest-hapi');

module.exports = function (mongoose) {
    var modelName = "building";
    var Types = mongoose.Schema.Types;
    var Schema = new mongoose.Schema({
        
        facilitiesPerFloor: [{
            suiteInfo: {
                floorNo: {
                    type: Types.Number
                }
            },
            facilities: [{
                type: Types.ObjectId,
                ref: "facility"
            }]
        }]

    }, { collection: modelName });

    Schema.statics = {
        collectionName: modelName,
        routeOptions: {
            associations: {
                //EXPL: dummy association that allows for the 'facilitiesPerFloor' value in the $embed parameter
                facilitiesPerFloor: {
                    type: "_MANY",
                    model: "facility",
                    allowAdd: false,
                    allowRemove: false,
                    allowRead: false
                }
            },
            list: {
                post: function (query, result, Log) {
                    const Facility = mongoose.model('facility');

                    if (!_.isArray(query.$embed)) {
                        query.$embed = [query.$embed]
                    }
                    if (query.$embed.indexOf('facilitiesPerFloor') > -1) {
                        //EXPL: first collect all the facility ids
                        const ids = result.reduce(function(ids, document) {
                            let docIds = [];
                            if (document.facilitiesPerFloor) {
                                docIds = document.facilitiesPerFloor.reduce(function(docIds, floor) {
                                    return docIds.concat(floor.facilities);
                                }, [])
                            }
                            return ids.concat(docIds);
                        }, []);

                        //EXPL: next fetch the facility documents and replace the ids with the matching documents
                        return RestHapi.list(Facility, { "_id": ids }, Log)
                            .then(function(facilities) {
                                result = result.map(function(document) {
                                    if (document.facilitiesPerFloor) {
                                        document.facilitiesPerFloor = document.facilitiesPerFloor.map(function(floor) {
                                            floor.facilities = floor.facilities.map(function(facilityId) {
                                                let facility = facilities.docs.find(function(facility) {
                                                    return facility._id.toString() === facilityId.toString();
                                                });
                                                return facility;
                                            });
                                            return floor;
                                        });
                                    }
                                    return document;
                                });
                                return result;
                            })
                    }
                    else {
                        return Q.when(result);
                    }
                }
            }
        }
    };

    return Schema;
};

[samseralam]

Thanks @JKHeadley
After creating association with facility model it works fine.