Get the first document using $in with mongodb - mongodb

Question

how can get the first element using in in mongo ?
if i've a list like ['car', 'house', 'cat', dog'], and a collection which contains many documents these element, i'd like to find the first document which contain cat, and first which contains dog etc.
I've tried to use limit() but in fact it gives me only one document, which can be either car, or dog or cat etc.
is there a way to combine a limit with $in ?
Thanks
EDIT:
example of data i've:
{
"_id": {
"$oid": "51d53ace9e674607e837d62d"
},
"sensors": [{
"name": "os-hostname",
"value": "yahourt"
}, {
"name": "os-domain-name",
"value": ""
}, {
"name": "os-platform",
"value": "Win32NT"
}, {
"name": "os-fullname",
"value": "Microsoft Windows XP Professional"
}, {
"name": "os-version",
"value": "5.1.2600.131072"
}],
"type": "os",
"serial": "2_os_os-hostname_yahourt"
} {
"_id": {
"$oid": "51d53ace9e674607e837d62e"
},
"sensors": [{
"name": "cpu-id",
"value": "_Total"
}, {
"name": "cpu-usage",
"value": 37.2257042
}],
"type": "cpu",
"serial": "2_cpu_cpu-id_total"
} {
"_id": {
"$oid": "51d53ace9e674607e837d62f"
},
"sensors": [{
"name": "cpu-id",
"value": "0"
}, {
"name": "cpu-usage",
"value": 48.90282
}],
"type": "cpu",
"serial": "2_cpu_cpu-id_0"
} {
"_id": {
"$oid": "51d53ace9e674607e837d630"
},
"sensors": [{
"name": "cpu-id",
"value": "1"
}, {
"name": "cpu-usage",
"value": 25.54859
}],
"type": "cpu",
"serial": "2_cpu_cpu-id_1"
} {
"_id": {
"$oid": "51d53ace9e674607e837d631"
},
"sensors": [{
"name": "volume-name",
"value": "C:"
}, {
"name": "volume-label",
"value": ""
}, {
"name": "volume-total-size",
"value": "52427898880"
}, {
"name": "volume-total-free-space",
"value": "20305170432"
}, {
"name": "volume-percent-free-space",
"value": "38"
}, {
"name": "volume-reads-per-second",
"value": 0.0
}, {
"name": "volume-writes-per-second",
"value": 9.324152
}, {
"name": "volume-read-bytes-per-second",
"value": 0.0
}, {
"name": "volume-write-bytes-per-second",
"value": 194141.6
}, {
"name": "volume-queue-length",
"value": 0.0
}],
"type": "disk",
"serial": "2_disk_volume-name_c"
}

Answer 1

You cannot add a limit to $in but you could cheat by using the aggregation framework:
db.collection.aggregate([
{$match:{serial:{$in:[list_of_serials]}}},
{$sort:{_id:-1}},
{$group:{_id:'$serial',type:{$first:'$type'},sensors:{$first:'$sensors'},id:{$first:'$_id'}}}
]);
Would get a list of all first found of each type.
Edit
The update will get the last inserted according to the _id.