Exclude Category from Custom Post Type Loop / Archive - categories

Question

I've been reading through posts on how to do this but none seem to make sense or work. I have created a custom post type (research) in my functions.php file and a custom taxonomy (classifications). I also have a custom archive page (archive-research.php) for my post type.
I have a category (classification) called "oldresearch" that I would like to exclude from the custom archive template.
Below is my custom post type code. Could someone please help me and let me know where the exclusion code needs to go.
<?php
/* redirect users to front page after login */
function redirect_to_front_page() {
global $redirect_to;
if (!isset($_GET['redirect_to'])) {
$redirect_to = get_option('siteurl');
}
}
add_action('login_form', 'redirect_to_front_page');
if ( function_exists('register_sidebars') )
register_sidebars(3);
add_action('init', 'register_custom_menu');
function register_custom_menu() {
register_nav_menu('custom_menu', __('Custom Menu'));
}
/** Registering Custom Post Type: Research **/
// Register Taxonomy for Research
$labels = array(
'name' => 'Classifications',
'singular_name' => 'Classification',
'search_items' => 'Search Classifications',
'popular_items' => 'Popular Classifications',
'all_items' => 'All Classifications',
'parent_item' => 'Parent Classifications',
'edit_item' => 'Edit Classifications',
'update_item' => 'Update Classifications',
'add_new_item' => 'Add New Classification',
'new_item_name' => 'New Classifications',
'separate_items_with_commas' => 'Separate Classifications with commas',
'add_or_remove_items' => 'Add or remove Classifications',
'choose_from_most_used' => 'Choose from most used Classifications'
);
$args = array(
'label' => 'Classifications',
'labels' => $labels,
'public' => true,
'hierarchical' => true,
'show_ui' => true,
'show_in_nav_menus' => true,
'args' => array( 'orderby' => 'term_order' ),
'rewrite' => array( 'slug' => 'research/classifications', 'with_front' => false ),
'query_var' => true
);
register_taxonomy( 'Classifications', 'Research', $args );
// Register Classification Column
add_filter( 'manage_research_posts_columns', 'ilc_cpt_columns' );
add_action('manage_research_posts_custom_column', 'ilc_cpt_custom_column', 10, 2);
function ilc_cpt_columns($defaults) {
$defaults['Classifications'] = 'Classifications';
return $defaults;
}
function ilc_cpt_custom_column($column_name, $post_id) {
$taxonomy = $column_name;
$post_type = get_post_type($post_id);
$terms = get_the_terms($post_id, $taxonomy);
if ( !empty($terms) ) {
foreach ( $terms as $term )
$post_terms[] = "<a href='edit.php?post_type={$post_type}&{$taxonomy}={$term->slug}'> " . esc_html(sanitize_term_field('name', $term->name, $term->term_id, $taxonomy, 'edit')) . "</a>";
echo join( ', ', $post_terms );
}
else echo '<i>No terms.</i>';
}
// Register Custom Post Type
function research_post_type() {
$labels = array(
'name' => _x( 'Research', 'Post Type General Name', 'text_domain' ),
'singular_name' => _x( 'Research', 'Post Type Singular Name', 'text_domain' ),
'menu_name' => __( 'Research', 'text_domain' ),
'parent_item_colon' => __( 'Parent Research', 'text_domain' ),
'all_items' => __( 'All Research', 'text_domain' ),
'view_item' => __( 'View Research', 'text_domain' ),
'add_new_item' => __( 'Add New Research', 'text_domain' ),
'add_new' => __( 'New Research', 'text_domain' ),
'edit_item' => __( 'Edit Research', 'text_domain' ),
'update_item' => __( 'Update Research', 'text_domain' ),
'search_items' => __( 'Search Research', 'text_domain' ),
'not_found' => __( 'No Research found', 'text_domain' ),
'not_found_in_trash' => __( 'No Research found in Trash', 'text_domain' ),
);
$rewrite = array(
'slug' => 'research',
'with_front' => true,
'rewrite_pages' => true,
'rewrite_feeds' => true,
);
$args = array(
'label' => __( 'research', 'text_domain' ),
'description' => __( 'Agri-Gro product research', 'text_domain' ),
'labels' => $labels,
'supports' => array( 'title', 'editor', 'excerpt', 'author', 'thumbnail', 'comments', 'trackbacks', 'revisions', 'custom-fields', 'page-attributes', 'post-formats', ),
'taxonomies' => array( 'Classifications', 'post_tag' ),
'hierarchical' => true,
'public' => true,
'show_ui' => true,
'show_in_menu' => true,
'show_in_nav_menus' => true,
'show_in_admin_bar' => true,
'menu_position' => 20,
'menu_icon' => 'http://www.agrigro.com/news/wp-content/uploads/2013/01/Documents-icon.png',
'can_export' => true,
'has_archive' => true,
'exclude_from_search' => false,
'publicly_queryable' => true,
'rewrite' => $rewrite,
'capability_type' => 'page',
);
register_post_type( 'research', $args );
}
// Hook into the 'init' action
add_action( 'init', 'research_post_type', 0 );
?>

Answer 1

You can use the pre_get_posts filter in your functions.php in order to alter the query for a specific post_type. This is not the only way to achieve the task,but in my opinion it is quite easiest
UPDATE
You need to exclude a custom taxonomy term from your query so, we have to set a tax_query object, so:
Example:
add_action('pre_get_posts','custom_get_posts');
function custom_get_posts($query) {
// We are not displaying the posts on admin panel and this is the main query
if ( !is_admin() && $query->is_main_query() ) {
//Define the tax_query
$taxquery = array(
array(
'taxonomy' => 'Classifications', // also try lower case, remember a taxonomy name must be in lowercase
'field' => 'slug',
'terms' => array( 'oldresearch' ),
'operator' => 'NOT IN'
)
);
// We are displaying a custom posts type archive
if( $query->is_post_type_archive( 'research' ) ){
$query->set('tax_query', $taxquery );
}
}
}
Hope it helps! Let me know if you get stuck.