How to get list of fields from Object in mongoDB? - php

Question

I'm new in mongoDB, I saw enough examples but most show how to work with collections.
I have followed data stored in mongoDB under DB name myDB:
"_id" : "some_table_name",
"content" : [{
"id" : "1",
"loctype" : "Clinic/Hospital",
"locname" : "KKH"
}, {
"id" : "2",
"loctype" : "Clinic/Hospital",
"locname" : "Singapore National Eye Centre"
}
}]
}
As you can see the model contains _id and content, where content is list of objects:
... ,
{
"id" : "ZZZ",
"loctype" : "ZZZ",
"locname" : "ZZZ"
},
...
PHP
$m = new MongoClient(/* ... */);
$db = $m->myDB;
$collection = $db->coll;
How can I fetch in PHP list of ids? a.e [1,2] in my case.
For sure I can get all model and extract ids but I try to do it stright from mongoDB.
Thanks.

Answer 1

It depends on how you want this formatted but here is a aggregation version which formats it in a nice way:
$mongo->collection->aggregate(array(
array('$unwind'=>'$content'),
array('$project'=>array('_id'=>'$content.id'))
))
It will print documents like:
[
{_id:1},
{_id:2}
]
Another way could be to just project the single field out with $db->collection->find(array(),array('content.id'=>1))
I should note though, it would most likely to better to just do this in PHP. Through PHP is the only way you can get the exact output you are seeking I believe.

Answer 2

Try this:
$collection = new MongoCollection($db, 'collection_name');
$query = array(
// Some restrictions can be here
);
$ids = array();
$cursor = $collection->find($query);
foreach ($cursor as $doc) {
$doc = (array) $doc;
$ids[] = $doc["id"];
}
var_dump($ids);

Answer 3

Use mapreduce followed by distinct, as follows:
mr = db.runCommand({
"mapreduce" : "things",
"map" : function() {
for (var key in this) { emit(key, null); }
},
"reduce" : function(key, stuff) { return null; },
"out": "things" + "_keys"
})
db[mr.result].distinct("_id")
["foo", "bar", "baz", "_id", ...]
Or use Variety...