useDeepPopulate.js

User.find(id).populate('preferences').exec(function (err, user) {
    if(err) {
        sails.log.error("ERR:", err);
    }
    sails.services['util'].populateDeep('user', user[0], 'preferences.nestedPreferences', function (err, newUser) {
        if (err) {
            sails.log.error("ERR:", err);
        }
        console.log(newUser);
    });

});

util.js

/**
 * Created by dinana on 25/4/15.
 * Please keep credits for re-use.
 */

function populateDeep2(parentModelName, parentModel, path, cb) {
    if( !path || path.length == 0 ) {
        cb("No path given");
        return;
    }
    var count = 0;
    var parent = JSON.parse(JSON.stringify(parentModel));
    populateDeepInner(parentModelName, parent, path, cb);
    function populateDeepInner(parentModelName, parentInstance, path, cb) {
        if(Array.isArray(parentInstance)) {
            count = count + parentInstance.length;
            parentInstance.map(function(value, index, origArray){
                handle(value)
            })
        } else {
            count++;
            handle(parentInstance)
        }

        function handle(parentInstance) {
            var pathArray = path.split('.');
            var childInstance = parentInstance[pathArray[0]]
            if (isPopulated(childInstance)) {
                doneIfDone(childInstance, pathArray);
            } else {
                var childAssociation = getChildModel(parentModelName, pathArray[0]);
                var findCriteria;
                switch (childAssociation.type) {
                    case 'model':
                        findCriteria = childInstance;
                        break;
                    case 'collection':
                        findCriteria = {};
                        findCriteria[childAssociation.via] = parentInstance.id;
                        break;
                }
                if(pathArray.length > 1) {
                    childAssociation.model.find(findCriteria)
                        .populate(pathArray[1]).exec(function (err, populatedChild) {
                            if(err) {
                                console.log("Error:",err)
                                cb(err)
                            }
//                            pathArray.splice(0,1)
                            stitcher(populatedChild);
                        })
                } else {
                    childAssociation.model.find(findCriteria)
                        .exec(function (err, populatedChild) {
                            if(err) {
                                console.log("Error:",err)
                                cb(err)
                            }
//                            pathArray.splice(0,1)
                            stitcher(populatedChild);
                        })
                }
            }
            function stitcher(newChildInstance) {
                newChildInstance = JSON.parse(JSON.stringify(newChildInstance));
                switch(getChildModel(parentModelName,pathArray[0]).type) {
                    case 'model':
                        parentInstance[pathArray[0]] = newChildInstance[0];
                        break;
                    case 'collection':
                        parentInstance[pathArray[0]] = newChildInstance;
                        break;
                }
                doneIfDone(newChildInstance)
            }
            // Assumptions: newChild is already populated
            function doneIfDone(newChildInstance) {
                if(pathArray.length > 1) {
                    var newPathArray = pathArray.slice(1)
                    var newPath = newPathArray.join('.');
                    count--;
                    populateDeepInner(getChildModel(parentModelName, pathArray[0]).modelName, newChildInstance, newPath, cb);
                } else {
                    count--;
                    if (count == 0)
                        cb(null, parent);
                }
            }
            function getChildModel(parentModelName, childModelName) {
                var childAssociation = sails.models[parentModelName.toLowerCase()].associations.filter(function (value) {
                    return value.alias == childModelName;
                })
                return {model:sails.models[childAssociation[0][childAssociation[0].type]], type:childAssociation[0].type, via: childAssociation[0].via, modelName:childAssociation[0][childAssociation[0].type]};
            }
        }
        function isPopulated(model) {
            return (model && typeof model != 'string')
        }
    }
}
 module.exports = {populateDeep:populateDeep2}