Help me with understanding mongodb, please. have three collections: threads, messages and users.
thread
{ "title" : "1212", "message" : "12121", "user_id" : "50ffdfa42437e00223000001", "date" : ISODate("2013-04-11T19:48:36.878Z"), "_id" : ObjectId("51671394e5b854b042000003") }
message
{ "message" : "text", "image" : null, "thread_id" : "51671394e5b854b042000003", "user_id" : "516d08a7772d141766000001", "date" : ISODate("2013-04-17T15:58:07.021Z"), "_id" : ObjectId("516ec68fb91b762476000001") }
user
{ "user" : "admin", "date" : ISODate("2013-04-16T08:15:35.497Z"), "status" : 1, "_id" : ObjectId("516d08a7772d141766000001") }
How can I display all messages for current thread and get user name (for comment) from users collection?
this code get only messages without user name
exports.getMessages = function(id, skip, callback) {
var skip = parseInt(skip);
messages.find({thread_id: id}).sort({date: 1}).skip(skip).limit(20).toArray(
function(e, res) {
if (e) {
callback(e)}
else callback(null, res)
});
};
Node.js and mongo native
Generally, Mongo uses embedded documents or references to maintain relationships. Here is a link from the mongo docs worth reading.
What you are currently doing is storing a manual reference to the user collection within your message collection. Mongo manual references require additional queries in order to get that referenced data. In this case, using a reference based relationship will work, but it would force the N+1 query problem. Meaning you will have to make an addition query for every message you wish to display plus the original query for messages. References are explained in further detail here. One solution would be to incorporate DBRefs, which would require language specific driver support.
Another alternative would be use embedded documents. In this case you would store the related user object embedded within the messages object. Here is another link to the mongo docs with a great example. In this case, you would make a single query, which will return all of the messages, with each related user object embedded inside. Although embedded documents encourage duplicate data, in many cases they provide performance benefits. All of this information is explained in the mongo docs and can be read in detail to further understand the data modeling of mongo.
Additionally, the mongoose library is pretty awesome and has a populate function which is helpful for references.