Question

I’m implementing a very simple conversation system on mongodb.

The idea should be that when I’m opening a convo, it should display send and received messages. It’s OK so far and should be pretty easy, by using a simple query like this pseudocode:

(from "my_id" AND to "friend_id") OR (from "friend_id" AND to "my_id")

this should be pretty straightforward and simple, but querying just looks so complicated to me with mongodb (I’m coming from mysql).

I’m trying this, but it’s not working at all, and can’t find out where the error is.

$cursor =$collection->find
            (
                array('$or' =>
                    array('$and' => array("from"=>"$profile", "to"=>"$loggeduser")),
                    array('$and' => array("to"=>"$profile", "from"=>"$loggeduser"))
                )
            )->limit(50)->sort(array('date' => -1));

this returns nothing…. Where’s the mistake?

Thanks in advance.

Answer 1

Take a look at this page on how to do advanced MongoDB queries: http://www.mongodb.org/display/DOCS/Advanced+Queries

You can use a combination of the $and and $in operators to get what you need. Using the mongo shell, your query would look something like this:

db.yourCollectionName.find({$and: {from: {$in: ["toUser", "loggedOnUser"]}}, {to: {$in: ["toUser", "loggedOnUser"]}}})

I believe this may also give you the equivalent:

db.yourCollectionName.find({$and: {$or: [{from: "toUser"}, {to: "toUser"}]}}, {$or: [{from: "loggedOnUser"}, {to: "loggedOnUser"}]}}})

From there it’s a matter of converting the above to the language/DSL that you’re using, and sorting by date.

In your code, you don’t need the ($and => array()) wrapping each of the objects that you’re trying to find. Remove them, so it looks like this:

$cursor = $collection->find(
    array('$or' => 
        array(
            array("from"=>"$profile", "to"=>"$loggeduser"),
            array("to"=>"$profile", "from"=>"$loggeduser")
        )
    )
) ->limit(50)->sort(array('date' => -1));