Extend model with count of related model - node.js

Question

I'm trying to build a simple blog with loopback. I want to extend get Posts with the amount of comments.
I have two possible ways in my mind.
1) Extend the response of the get-posts by a count of the comments, this would be my favorite way, but I have no idea how to extend the reposne.
2) I have tried to observe the comment saving and to get the posts-model, but I can't change it.
post.json
{
"name": "post",
"base": "PersistedModel",
"idInjection": true,
"options": {
"validateUpsert": true
},
"properties": {
"title": {
"type": "string",
"required": true
},
"content": {
"type": "string",
"required": true
}
"published": {
"type": "boolean",
"required": true,
"default": false
}
"commentCount": {
"type": "number",
"default": 0
}
},
"validations": [],
"relations": {
"user": {
"type": "belongsTo",
"model": "user",
"foreignKey": ""
},
"comments": {
"type": "hasMany",
"model": "comment",
"foreignKey": ""
}
},
"acls": [
{
"accessType": "*",
"principalType": "ROLE",
"principalId": "$everyone",
"permission": "DENY"
},
{
"accessType": "*",
"principalType": "ROLE",
"principalId": "admin",
"permission": "ALLOW"
},
{
"accessType": "EXECUTE",
"principalType": "ROLE",
"principalId": "admin",
"permission": "ALLOW",
"property": "find"
},
{
"accessType": "EXECUTE",
"principalType": "ROLE",
"principalId": "$authenticated",
"permission": "ALLOW",
"property": "create"
},
{
"accessType": "READ",
"principalType": "ROLE",
"principalId": "$owner",
"permission": "ALLOW"
},
{
"principalType": "ROLE",
"principalId": "$authenticated",
"permission": "ALLOW",
"property": [
"__create__comments",
"__get__comments"
]
},
{
"principalType": "ROLE",
"principalId": "$owner",
"permission": "ALLOW",
"property": "__delete__comments"
}
],
"methods": {}
}
comment.json
{
"name": "comment",
"base": "PersistedModel",
"idInjection": true,
"options": {
"validateUpsert": true
},
"properties": {
"content": {
"type": "string",
"required": true
}
},
"validations": [],
"relations": {
"user": {
"type": "belongsTo",
"model": "user",
"foreignKey": ""
},
"idea": {
"type": "belongsTo",
"model": "post",
"foreignKey": ""
}
},
"acls": [
{
"accessType": "*",
"principalType": "ROLE",
"principalId": "$everyone",
"permission": "DENY"
},
{
"accessType": "*",
"principalType": "ROLE",
"principalId": "admin",
"permission": "ALLOW"
},
{
"accessType": "READ",
"principalType": "ROLE",
"principalId": "$authenticated",
"permission": "ALLOW"
},
{
"accessType": "*",
"principalType": "ROLE",
"principalId": "$owner",
"permission": "ALLOW"
}
],
"methods": {}
}
comment.js ##
var loopback = require('loopback');
module.exports = function(Comment) {
Comment.observe('after save', function(ctx, userInstance, next) {
var postId = ctx.instance.postId;
// loopback.getModel('post').definition.rawProperties.commentCount... something... something...
});
};
I'm still very new to loopback and I don't know what is the best way to achieve the solution. Maybe you have a third, better way? Or maybe anyone can help me to complete the comment.js.

Answer 1

Fisrt, in your comment.json, you've written idea instead of post:
"post": { //change here
"type": "belongsTo",
"model": "post",
"foreignKey": ""
}
Secondly, you simply add one commentCount in the post linked to your comment in your after save method and then update the attributes of your post:
'use strict';
var app = require('../../server/server');
var models = app.models;
var Post;
// pattern to get your models on start event
app.on('started', function () {
Post = models.post;
});
module.exports = function(Comment) {
Comment.observe('after save', function(ctx, next) {
// only add a commentCount if it's a new instance
if (ctx.instance && ctx.isNewInstance && ctx.instance.postId) {
Post.findOne({where: {id: ctx.instance.postId}}, function (err, post) {
if (!err) {
post.updateAttributes({commentCount: post.commentCount++});
}
});
}
next();
});
};
Another solution would be to create a customGet endpoint in your post.js file:
'use strict';
module.exports = function(Post) {
Post.customGet = function (postId, cb) {
Post.findOne({where: {id: postId}, include: 'comments'}, function (err, post) {
if(err){
return cb(err, {});
}
post.commentCount = post.comments.length;
return cb(err, post);
});
}
Post.remoteMethod('customGet', {
description: 'New endpoint with the commentCount',
accepts: {arg: 'postId', type: 'string'},
returns: {arg: 'post', type: 'object'},
http: {verb: 'get'}
});
};
You can improve this method a bit but you get the idea.