MongoDB sorting

Question

I want implement a \"bump\" feature for topics. Once a topic is bumped, it will have a new \"bump_date\" field. I want to sort it so that when there is a \"bump_date\" fie

Answer 1

Currently it is not possible in mongodb to do a sort based on user defined criteria over multiple columns.eg. here the function would have been to return bump_date if it is set,else return created

Either you will have to use a server-side or client-side code as mentioned here :

Mongo complex sorting?

or if you want to stay with basic quering and sorting, you shall :

• create a key bump_date equivalent to created whenever a new record is created. This will not be a data overhead, as you can expect every topic of yours to be bumped once in a while in future,hence bump_date field will eventually be added. So add it from the start itself.

• Whenever the article is bumped,update the field bump_date .

Your example documents will look like this with this change :

{
    "text" : "test 1",
    "created" : "Sun Nov 20 2011 02:03:28 GMT-0800 (PST)",
    "bump_date" : "Sun Nov 20 2011 02:03:28 GMT-0800 (PST)"
},
{
    "text" : "test 2",
    "created" : "Sun Nov 18 2011 02:03:28 GMT-0800 (PST)",
    "bump_date" : "Sun Nov 18 2011 02:03:28 GMT-0800 (PST)" 
},
{
    "text" : "test 3",
    "created" : "Sun Nov 17 2011 02:03:28 GMT-0800 (PST)",
    "bump_date: : "Sun Nov 19 2011 02:03:28 GMT-0800 (PST)"
}

You shall ensureIndex on bump_date field. Now you can query the required data easily.

db.topics.find().sort({ bump_date: 1 })