Question

I have articles which are sorted by their rating using .sort( { rating : -1 } )

I have a lot of articles which do not have any rating (In the DB side, they haven’t even the rating key). In the front end, I show them with a rate of 0.5 of 1.

When I sort the articles, I have now this order :

1 1 0.89 0.7 0.5 0.2 0.1 0 0 0 0 0 no_key no_key no_key no_key no_key no_key...

But, I would like to take in account that no_key is more a 0.5 rating than a zero (even lower in the previous sorting). So, I would like something like this :

1 1 0.89 0.7 0.5 no_key no_key no_key no_key no_key no_key... 0.2 0.1 0 0 0 0 0 

I want to avoid to have to fill the missing rating keys of the unrated articles by 0.5.

Any tricks ? Any Ideas ?

Answer 1

So, this requires three separate queries, but until the Aggregation framework ( http://www.mongodb.org/display/DOCS/Aggregation+Framework ) comes out, it’s probably the best way:

> db.test.save({rating:1});
> db.test.save({rating:2});
> db.test.save({rating:3});
> db.test.save({rating:4});
> db.test.save({rating:0.5});
> db.test.save({rating:0});
> db.test.save({rating:0}); 
> db.test.save({rating:0});
> db.test.save({rating:-1});
> db.test.save({});
> db.test.save({});
> db.test.save({});
> db.test.find({rating:{$gte:.5}}).sort({rating:-1});
{ "_id" : ObjectId("4f52c707621918e231bc55da"), "rating" : 4 }
{ "_id" : ObjectId("4f52c705621918e231bc55d9"), "rating" : 3 }
{ "_id" : ObjectId("4f52c703621918e231bc55d8"), "rating" : 2 }
{ "_id" : ObjectId("4f52c700621918e231bc55d7"), "rating" : 1 }
{ "_id" : ObjectId("4f52c70b621918e231bc55db"), "rating" : 0.5 }
> db.test.find({rating:{$exists:false}});
{ "_id" : ObjectId("4f52c718621918e231bc55e0") }
{ "_id" : ObjectId("4f52c719621918e231bc55e1") }
{ "_id" : ObjectId("4f52c71a621918e231bc55e2") }
> db.test.find({rating:{$lt:.5}}).sort({rating:-1});
{ "_id" : ObjectId("4f52c70e621918e231bc55dc"), "rating" : 0 }
{ "_id" : ObjectId("4f52c712621918e231bc55dd"), "rating" : 0 }
{ "_id" : ObjectId("4f52c712621918e231bc55de"), "rating" : 0 }
{ "_id" : ObjectId("4f52c714621918e231bc55df"), "rating" : -1 }