MongoDB finding nested objects that meet criteria

问题

I have a MongoDB document that is structured similar to the structure below follows. I am searching based on people.search_columns.surname and people.columns.givenname. So for example, when I search for the given name of "Valentine", I want to get the document back, but Nicholas Barsaloux should not be included.

Data structure:

[_id] => MongoId Object (
    [$id] => 53b1b1ab72f4f852140dbdc9
)
[name] => People From 1921
[people] => Array (
    [0] => Array (
        [name] => Barada, Valentine
        [search_columns] => Array (
            [surname] => Array (
                [0] => Mardan,
                [1] => Barada
            )
            [givenname] => Array (
                [0] => Valentine
            )
        )
    )
    [1] => Array (
        [name] => Barsaloux, Nicholas
        [search_columns] => Array (
            [surname] => Array (
                [1] => Barsaloux
            )
            [givenname] => Array (
                [0] => Nicholas
            )
            [place] => Array (
            )
        )
    )
)

Here is the code I was working on:

$criteria = array("people" => array(
        '$elemMatch' => array("givenname" => "Valentine")
));

$projection = array("people" => true);

$documents_with_results = $db->genealogical_data->find($criteria, $projection)->skip(0)->limit(5); 

Currently that code returns zero results.

回答1:

Since the arrays are nested you cannot use basic projection as you can with find. Also in order to "filter" the array contents from a document you need to "unwind" the array content first. For this you use the aggregation framework:

   $results = $db->genealogical_data->aggregate(array(
       array( '$match' => array(
           'people.search_columns.givenname' => 'Valentine'
       )),
       array( '$unwind' => '$people' ),
       array( '$match' => array(
           'people.search_columns.givenname' => 'Valentine'
       )),
       array( '$group' => array(
           '_id' => '$id',
           'name' => array( '$first' => '$name' ),
           'people' => array( '$push' => '$people' )
       ))
   ));

The point of the first $match stage is to reduce the documents that possibly match your criteria. The second time is done after the $unwind, where the actual "array" items in the document are "filtered" from the results.

The final $group puts the original array back to normal, minus the items that do not match the criteria.

来源：https://stackoverflow.com/questions/24499362/mongodb-finding-nested-objects-that-meet-criteria