查询与子表上的where子句的关系

I have been using the has method to query the existence of data in a related table and that is working just fine. Using the code example on the Laravel web site, you can do the following to get any post that has comments associated with it.

$posts = Post::has('comments')->get();

What I would like to be able to do, as an example, is query for any post which has comments from the last thirty days. Since the has method only has the ability to count related rows I am not sure of a good way to do this.

From the Laravel 4 Documentation:

 $posts= Post::with(array('comments' => function($query)
 {
    $query->where('published', '>=', 'date- 1 month'); //look date functions up
 }))->get();

See Eager Load Constraints under laravel 4 documentation

Ok, this is what I could come up with. It might not be the best solution, but it does work and doesn't seem too polluted. First, we'll need to add reference to Carbon and the Eloquent\Collection classes.

use \Carbon\Carbon;
use \Illuminate\Database\Eloquent\Collection;

Carbon does come with Laravel as a dependency, out of the box, but it would be smart to add it to your own project's dependencies anyway. Then, this code should do it:

// Gather all distinct 'post_id' from Comments made in the last 30 days
// along with its Post objects
$comments = Comment::with('Post')
                   ->where('created_at', '>', Carbon::now()->subMonth())
                   ->distinct()
                   ->get(array('post_id'));

// Since we only want Posts, loop through the Comments collection and add
// the Posts to a new collection
$posts = new Collection;
foreach ($comments as $comment) {
    $posts->add($comment->post);
}