How to get list of fields from Object in mongoDB?

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.

Sammaye · Accepted Answer · 2013-05-28 10:58:05Z

2

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.

edited May 28, 2013 at 10:58

answered May 28, 2013 at 10:52

Sammaye

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2 Comments

Sammaye Over a year ago

@MaximShoustin True, converted to PHP

Sammaye Over a year ago

@MaximShoustin There is a serious troll some where, I get a lot of answers downvoted recently, it is rather annoying :/

Bogdan Burym · Accepted Answer · 2013-05-28 10:50:26Z

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);

answered May 28, 2013 at 10:50

Bogdan Burym

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Comments

hd1 · Accepted Answer · 2013-05-28 11:20:42Z

1

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...

answered May 28, 2013 at 11:20

hd1

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