Eloquentのモデル生成法比較：newとcreate ref: http://qiita.com/asaokamei/items/bdad9d0f931f0840a3a9

file0.php

$entity1 = new Model();
$entity2 = Model::create( array() );

file1.php

class Blog extends Eloquent {
  public comments() {
    return $this->hasMany('Comment');
  }
}
class Comment extends Eloquent {
  public blogs() {
    return $this->BelongsTo('Blog');
  }
}

file2.php

$blog = new Blog();
$comment = new Comment();
$blog->comment()->save($comment); // 例外発生！

file3.php

$blog = Blog::create(array());
$comment = Comment::create(array());
$blog->comment()->save($comment); // 問題なし！