How to perform a search inside a specific taxonomy category

Question

My problem is this: I have 3 custom taxonomies, let's say 'author', 'title' and 'editor', each one applied to regular posts. Let's say I have post_1 that has in the 'author' field 'jorge borges' and post_2 that has 'ray bradbury'.

I'm trying to have a search form with a drop down menu containing the three taxonomies and a text field, so that if I select, i.e., 'author' and search for 'jorge borges', the result will be post_1.

The other two taxonomies should work like this as well.

I couldn't find anything similar, as many questions concern the creation of a drop down menu with all instances of a taxonomy, which is not what I want. I want a drop down menu with taxonomy categories, not values.

Answer 1

Ok, here is something that I have come up with and tested on my site.

Note that this is quite raw (I.e. no styling), and you'll probably need to add some resiliency to it just in case you get some unexpected results, but that is all up to you I'm afraid.

Here is the search form. I've not added an action because I don't know where you want to redirect the form. However, by default you will be directed back to the same page, so you can just query the posts there.

<form method="POST">
    <h3>Search for posts</h3>
<?php
    $taxonomies[] = get_taxonomy('author');
    $taxonomies[] = get_taxonomy('title');
    $taxonomies[] = get_taxonomy('editor');
    $options = array();

    if(!empty($taxonomies)) : foreach($taxonomies as $taxonomy) :
            if(empty($taxonomy)) : continue; endif;
            $options[] = sprintf("\t".'<option value="%1$s">%2$s</option>', $taxonomy->name, $taxonomy->labels->name);
        endforeach;
    endif;

    if(!empty($options)) :
        echo sprintf('<select name="search-taxonomy" id="search-taxonomy">'."\n".'$1%s'."\n".'</select>', join("\n", $options));
        echo '<input type="text" name="search-text" id="search-text" value=""></input>';
        echo '<input type="button" name="search" id="search" value="Search"></input>';
    endif;
?>
</form>

Now, add this just before you output your posts -

if(!empty($_POST['search-text'])) :
    $args = get_search_args();
    query_post($args);
endif;

Finally, add this to your function.php so that you can go grab the relevant $args

function get_search_args(){

    /** First grab all of the Terms from the selected taxonomy */
    $terms = get_terms($_POST['search-taxonomy'], $args);
    $needle = $_POST['search-text'];

    /** Now get the ID of any terms that match the text search */
    if(!empty($terms)) : foreach($terms as $term) :

            if(strpos($term->name, $needle) !== false || strpos($term->slug, $needle) !== false) :
                $term_ids[] = $term->term_id;
            endif;

        endforeach;
    endif;

    /** Construct the args to use for quering the posts */
    $args = array(
        'order'         => ASC,
        'orderby'       => 'name',
        'post_status'   => 'publish',
        'post_type'     => 'post',
        'tax_query'     => array(
            array(
                'taxonomy'  => $_POST['search-taxonomy'],
                'field'     => 'term_id',
                'terms'     => $term_ids,
                'operator'  => 'IN'
            )
        )
    );

    return $args();

}