Using $slice with $regex together on subDocument array in mongodb - regex

Question

Hi I am stuck on a problem in mongo. Let me first show you an example of the data. This is a record from my table.
{
"_id": "3691149613248",
"following": [{
"content_id": "2584833593728",
"date": "2015-08-20 12:46:55"
}, {
"content_id": "3693447751360",
"date": "2015-09-11 12:17:55"
}, {
"content_id": "2582396936896",
"date": "2015-09-12 07:04:02"
}, {
"content_id": "3697346507456",
"date": "2015-09-14 09:56:03"
}, {
"content_id": "3697755500800",
"date": "2015-09-16 10:05:51"
}, {
"content_id": "2589701320192",
"date": "2015-09-16 10:51:19"
}, {
"content_id": "2585723555136",
"date": "2015-09-16 11:40:26"
}, {
"content_id": "3695996668352",
"date": "2015-09-16 12:50:25"
}, {
"content_id": "3694290368512",
"date": "2015-09-16 12:50:33"
}, {
"content_id": "3691210127552",
"date": "2015-09-16 13:02:57"
}, {
"content_id": "3694134958464",
"date": "2015-09-16 13:06:17"
}, {
"content_id": "3697315148736",
"date": "2015-09-17 06:58:35"
}, {
"content_id": "3692104837824",
"date": "2015-09-17 12:19:12"
}, {
"content_id": "3693400309376",
"date": "2015-09-22 05:43:04"
}]
}
I want to fetch following array with condition that only specific records to fetch i.e. content_ids with prefix 369 and fetch number of content_id specified in limit and offset.
I am using $slice for fetching records for given limit & offset for following array. But how to filter content_id along with $slice.
My current query:
db.collectionName.find({
_id: "3691149613248"
}, {
"following": {
"$slice": [0, 10]
}
});
This is fetching following array with content_id that is specified in limit & offset. But it is fetching all content_id including prefix 258& 369 but I only need content_id with prefix 369 using mongo query.
Can any one help??

Answer 1

You can use combination of $unwind and $match with mongo aggregation to get expected output like:
db.collection.aggregate({
$match: {
"_id": "3691149613248" // you can skip this condition if not required
}
}, {
$unwind: "$following"
}, {
$match: {
"following.content_id": {
$regex: /^369/
}
}
}, {
$group: {
_id: "$_id",
"following": {
$push: "$following"
}
}
})
If you want to apply skip and limit to above query then you can easily use it like:
db.collection.aggregate({
$match: {
"_id": "3691149613248" //use this if you want to filter out by _id
}
}, {
$unwind: "$following"
}, {
$match: {
"following.content_id": {
$regex: /^369/
}
}
}, {
$skip: 4 // you can set offset here
}, {
$limit: 3 // you can set limit here
}, {
$group: {
_id: "$_id",
"following": {
$push: "$following"
}
}
})
EDIT :
If you are using php version less than 5.4 then query will be as:
$search = "369";
$criteria = array(array("$match" => array("_id" => "3691149613248")),
array("$unwind" => "$following"),
array("$match" => array("following.content_id" => array("$regex" => new MongoRegex("/^$search/")))),
array("$skip" => 4), array("$limit" => 3),
array("$group" => array("_id" => "$_id", "following" => array("$push" => "$following"))));
$collection - > aggregate($criteria);
If you are using PHP version greater than 5.3 then just replace { and } braces with [ and ] respectively.