Mongodb：将字段更改为数组

Lets say we have a document like this

{
    "_id" : "1234",
    "Data" : {
         "Name" : "Pythagoras",
         "Like" : "Math"
}

And we changed over mind and want to push more things to Data->Like so it looks like;

{
    "_id" : "1234",
    "Data" : {
         "Name" : "Pythagoras",
         "Like" : ["Math", "Science"]
}

All the atomic operators like $push, $pushAll and $addToSet works just when Data->Like already is an array.

I´m using the php-driver. In this example there is no meaning to not set the Data->Like to an array at the beginning but it does not work like that in my code ;(

Hope you can help me and sorry for my bad English ;) Thanks!

You'll have to iterate over all your documents and change the value to an array. For example, you can do that with:

$m = new Mongo();
$c = $m->yourdbname->yourcollectionname;

foreach ( $c->find() as $r )
{
    if ( !is_array( $r['Data']['Like'] ) )
    {
        $c->update( array( '_id' => $r['_id'] ), array( '$set' => array( 'data.like' => array( $r['data']['like'] ) ) ) );
    }
}