{
    "total":2,
    "data":[
      {
        "id":2,
        "user":{
          "id":1,
          "username":"sandro.tchikovani"
        },
        "description":"cool",
        "nb_comments":0,
        "nb_likes":0,
        "date_creation":"2014-04-13T20:07:34-0700"
      },
      {
        "id":1,
        "user":{
           "id":1,
           "username":"sandro.tchikovani",
         },
        "description":"Premier pooooste #lol",
        "nb_comments":0,
        "nb_likes":0,
        "date_creation":"2014-04-13T15:15:35-0700"
      }
    ]
 }

Class array<MoodressBundlePosteBundleEntityPoste> does not exist

$lastPosts = $serializer->deserialize($data['data'], 'array<MoodressBundlePosteBundleEntityPoste>', 'json');

$person = $serializer->deserialize($data,'AcmePerson','xml');

$person = $serializer->deserialize($data['data'],'MoodressBundlePosteBundleEntityPoste','json');

$data = json_decode($yourJsonFile, true);

foreach($data['data'] as $result)
{
    /* Here you can hydrate your object manually like:
    $person = new Person();
    $person->setId($user['id']);
    $person->setDescription($user['description']);

    Or you can use a denormalizer. */
}