Sorting objects in array within mongodb - mongodb

Question

I've seen this question all over google/SO/mongo docs, and I've tried to implement the solution, but it's not working for me. I have the following test database:
> db.test.find().pretty()
{
"_id" : ObjectId("56b4ab167db9acd913ce6e07"),
"state" : "HelloWorld",
"items" : [
{
"guid" : "123"
},
{
"guid" : "124"
},
{
"guid" : "123"
}
]
}
And I want to sort by the "guid" element of items. Running the sort commands yields:
> db.test.find().sort( {"items.guid" : 1}).pretty()
{
"_id" : ObjectId("56b4ab167db9acd913ce6e07"),
"state" : "HelloWorld",
"items" : [
{
"guid" : "123"
},
{
"guid" : "124"
},
{
"guid" : "123"
}
]
}
How can I sort by the "guid" element, so that the returned output of "items" is the 123, 123, and 124 guids (essentially move the child elements of "items" so that they're sorted by "guid")?
EDIT: I've also tried to use the $orderby command, doesn't accomplish what I want:
> db.test.find({ $query : {}, $orderby: {'items.guid' : 1} }).pretty()
{
"_id" : ObjectId("56b4ab167db9acd913ce6e07"),
"state" : "HelloWorld",
"items" : [
{
"guid" : "123"
},
{
"guid" : "124"
},
{
"guid" : "123"
}
]
}

Answer 1

Here is how it can be done using aggregate
db.test.aggregate([
{
$unwind : '$items'
},
{
$sort : {'items.guid' : 1}
},
{
$group : {
_id : '$_id',
state : {$first : '$state'},
items : {
$push : {'guid' : '$items.guid'}
}
}
}
]).pretty()
This is the output from this command.
{
"_id" : ObjectId("56b4ab167db9acd913ce6e07"),
"state" : "HelloWorld",
"items" : [
{
"guid" : "123"
},
{
"guid" : "123"
},
{
"guid" : "124"
}
]
}