MongoDB - upsert involving lists

Question

I\'m a MongoDB newbie and wanted to ask how to write an update command involving upsert and list.

Basically I want to accomplish something like this:

Answer 1

EDITED TO INCLUDE CORRECT SOLUTION

This is exactly the problem I hit learning Mongo - you're looking for the $addToSet operator (see docs here) that's used with the update command, in conjunction with the $ positional operator you were using.

$addToSet

{ $addToSet : { field : value } }

Adds value to the array only if its not in the array already.

The query thus becomes (db.stack is the collection I used for testing purposes), sample run to follow:

db.stack.update({ "trips.name":"2010-05-10" }, 
                { $addToSet: { "trips.$.loc":{"lat":11, "lng":12} } }
               );

TEST RUN (with some abbreviations for space of the elements that aren't important):

#### YOUR ITEM IN THE DB
> db.stack.find({"trips.name":"2010-05-10"})
{ "_id" : ObjectId("4c28f62cbf8544c60506f11d"), "some_other_data" : "goes here", 
    "trips" : [
    { "name" : "2010-05-10",
        "loc" : [ {
                "lat" : 21.321231,
                "lng" : 16.8783234,
                "updated_at" : "Mon May 10 2010 15:24:35"
            }, { "lat" : 21.321231,
                "lng" : 16.8783234,
                "updated_at" : "Mon May 10 2010 15:24:24"
            } ] },
    { "name" : "2010-05-08",
        "loc" : [ ... ]
    } ] }
#### SUCCESSFULLY ADDS ITEM TO PROPER ARRAY
> db.stack.update({"trips.name":"2010-05-10"}, {$addToSet: {"trips.$.loc":{"lat":11, "lng":11}}});
> db.stack.findOne()
{ "_id" : ObjectId("4c28f62cbf8544c60506f11d"), "some_other_data" : "goes here",
    "trips" : [
        { "loc" : [
                { "lat" : 21.321231,
                    "lng" : 16.8783234,
                    "updated_at" : "Mon May 10 2010 15:24:35"
                }, { "lat" : 21.321231,
                    "lng" : 16.8783234,
                    "updated_at" : "Mon May 10 2010 15:24:24"
                }, { "lat" : 11,
                    "lng" : 11
                }
            ], "name" : "2010-05-10"
        },
        { "name" : "2010-05-08",
            "loc" : [ ...  ]
        } ] }
#### ON REPEAT RUN DOESN'T ADD NEW ELEMENT
> db.stack.update({"trips.name":"2010-05-10"}, {$addToSet: {"trips.$.loc":{"lat":11, "lng":11}}});
> db.stack.findOne()
{ "_id" : ObjectId("4c28f62cbf8544c60506f11d"), "some_other_data" : "goes here",
    "trips" : [ {
            "loc" : [
                { "lat" : 21.321231,
                    "lng" : 16.8783234,
                    "updated_at" : "Mon May 10 2010 15:24:35"
                }, { "lat" : 21.321231,
                    "lng" : 16.8783234,
                    "updated_at" : "Mon May 10 2010 15:24:24"
                }, { "lat" : 11,
                    "lng" : 11
                }
            ], "name" : "2010-05-10"
        },
        { "name" : "2010-05-08",
            "loc" : [ ...  ]
        } ] }
#### BUT WILL CORRECTLY ADD ANOTHER ELEMENT TO THE SAME ARRAY IF IT'S NOT PRESENT
> db.stack.update({"trips.name":"2010-05-10"}, {$addToSet: {"trips.$.loc":{"lat":11, "lng":12}}});
> db.stack.findOne()
{ "_id" : ObjectId("4c28f62cbf8544c60506f11d"), "some_other_data" : "goes here",
    "trips" : [
        { "loc" : [
                { "lat" : 21.321231,
                    "lng" : 16.8783234,
                    "updated_at" : "Mon May 10 2010 15:24:35"
                }, { "lat" : 21.321231,
                    "lng" : 16.8783234,
                    "updated_at" : "Mon May 10 2010 15:24:24"
                }, { "lat" : 11,
                    "lng" : 11
                }, { "lat" : 11,
                    "lng" : 12
                }
            ], "name" : "2010-05-10"
        },
        { "name" : "2010-05-08",
            "loc" : [ ... ]
    } ] }