Add filter to get_posts

Question

So I am attempting to filter out certain posts in the get_posts call. Essentially, I want to be able to specify a certain block of posts, and only get the posts that correspond with the block. Right now I have a table that contains both block IDs and post IDs, so I have been looking into using the posts_join and the posts_where hooks. However, I need to be able to dynamically modify the block retrieved depending on what the client currently has chosen. To this end, I am tracking what the client has selected using a cookie. I feel that I should be able to pass the block ID as a another value in the array given to get_posts, but I have no idea how to retrieve that value. So my question is: how should I go about doing this?

It seems that the simplest, most elegant solution would be to just add something like:

$postargs = array(
    'blockID' => $id
);
$posts = get_posts($postargs);

I just don't know how in my hooked function:

function set_block_filter($id){
    /* This should probably use the posts_join hook */
    /* $join = 'LEFT JOIN wdpress.$table_name ON wdpress.$table_name.post_id = wdpress.wp_posts.ID'*/
    /* something like that ^ http://codex.wordpress.org/Plugin_API/Filter_Reference/posts_join*/
    /* $where = ' AND block_id=$id '*/
}

can retrieve the blockID from the $postargs array.

EDIT: So the solution was actually very simple, and I think most of my confusion was born from my misunderstanding about how cookies work. Since they are apparently accessible server-side, my answer was this:

function set_block_filter($query){
    if($query->is_category){
        $query->set('meta_key', 'block');
        $query->set('meta_value', $_COOKIE['block']);
        return;
    }
}

add_action('pre_get_posts','set_issue_filter');

Answer 1

Why not use the include (or conversely, exclude) argument for get_posts()? It takes an array of post IDs.

Answer 2

Depending on the flow of interaction I would store the information in either user_meta or post_meta. If the user chooses a block and it doesn't change very ofter I would save it in the user_meta table. This is the same way WordPress tracks your current dashboard preferences in the admin panel.

Or you could use both. Save the different blocks in post_meta and the users current choice in user_meta.

I would use Ajax just because with WordPress it's so easy and you don't have to reload the page. This of course depends on your UI flow.

<select name="post-block" id="<?php echo get_current_user_id(); ?>">
<option value="_block-value1">Block Value 1</option>
<option value="_block-value2">Block Value 2</option>
</select>

jQuery(document).ready(function($){
    var userID = $("select [name='post-block']").attr("id");

    $("select [name="post-block"]").change(function() {
          var option ="";
        $("select option:selected").each(function () {
         option += $(this).val();
     });
          $.ajax({ type: "POST", 
                    url: ajaxurl, 
                   data: {"action": "select-block", user_id: userID, user_option: option },
           success: function(response) {
           alert('The database said: ' + response);
       }
  });

PHP

    add_action( 'wp_ajax_nopriv_select-block', 'update_block_options' );
    function update_block_options() {
         $user_id = intval( $_POST['user_id'] );
         $block_option = $_POST['user_option'];

        $option_array = get_post_meta( $post->ID, $block_option, true);
          update_user_meta( $user_id, 'user_block_options', (array) $option_array );

          if (get_user_meta( $user_id,  'user_block_options' )
          $response = get_user_meta( $user_id,  'user_block_options';
          else $response = "Ooops something went wrong....";

           echo $response;
           die(1);
      }

To get the options before you run get_posts:

 $exclude_array = get_user_meta( get_current_user_id(), 'user_block_options' );
 $posts = get_posts( array('exclude' => (array)($exclude_array() );