Search custom post type by year - php

Question

I've created a more advanced search for the standard Wordpress search. To go along with the keyword text input I've added two drop downs that are searching my custom taxonomies.
This is working great.
The only dropdown I've yet to create the functionality for is the year dropdown. I'd like to be able to filter the results to show posts within that specific year.
How can I search through all the posts and only output the custom posts that were published for that year?
It's important that the posts are searched for by their publish date (ie. no custom fields!).
<form action="<?php echo home_url( '/' ); ?>" method="get" id="advanced-search">
<div id="search-nudge">
<h1 id="search-title">Search Policy's</h1>
<p id="search-strap">Search by some or all of the following criteria</p>
<div class="clear"></div>
<div id="search-left">
<p class="search-label">Keyword</p>
<input type="text" name="s" id="s" class="keyword" value="<?php the_search_query(); ?>" />
<input type="hidden" value="policies" name="post_type" id="post_type" /><br /><br />
</div>
<div id="search-right">
<p class="search-label">Year of publication</p>
<select class="work-list search-dropdown" name="year">
<option value="">All</option>
</select>
<div class="clear"></div>
</div>
<div class="clear"></div>
<div class="search-element">
<?php // List all event subjects
$subjectList = get_terms('topics', array( 'taxonomy' => 'topics' ));
if(!empty($subjectList)) { ?>
<p class="search-label">Category</p>
<select class="work-list search-dropdown" name="subject">
<option value="">All</option>
<?php foreach($subjectList as $subject){
if(isset($_GET['subject'])) {
$selected = ($subject->slug == $_GET['subject']) ? ' selected="selected"' : '';
}
echo '<option value="' . $subject->slug . '"'. $selected.'> ' . $subject->name . '</option>';
}
echo '</select><br /><br />';
} ?>
</div>
<div class="search-element">
<?php // list all event types
$document = get_terms('document_type', array( 'taxonomy' => 'document_type' ));
if(!empty($subjectList)) { ?>
<p class="search-label">Document Type</p>
<select class="work-list search-dropdown search-dropdown-right" name="type">
<option value="">All</option>
<?php foreach($document as $type){
if(isset($_GET['type'])) {
$selected = ($type->slug == $_GET['type']) ? ' selected="selected"' : '';
}
echo '<option value="' . $type->slug . '"'. $selected.'> ' . $type->name . '</option>';
}
echo '</select><br /><br />';
} ?>
</div>
<input type="radio" name="sort" class="search-input" value="date" checked> <p class="search-label radio radio-nudge">Order by date</p>
<input type="radio" name="sort" class="search-input" value="title"> <p class="search-label radio">Order by title</p>
<input type="submit" id="searchsubmit2" class="search-submit" value="Search" />
<div class="clear"></div>
</div>
</form>
<?php if(isset($_GET['sort']) && $_GET['sort'] === "date") {
$sort = $_GET['sort'];
$order = "DESC";
} else {
$sort = $_GET['sort'];
$order = "ASC";
}
// default args to search by custom post type and search term
$args = array(
'post_type' => 'policies',
'posts_per_page' => 10,
'orderby' => $sort,
'order' => $order,
's' => $s
);
// add the subject to args if there is one
if(isset($_GET['subject']) && $_GET['subject'] != "") {
$args['tax_query'][1] = array(
'taxonomy' => 'topics',
'field' => 'slug',
'terms' => array($_GET['subject'])
);
}
// add the subject to args if there is one
if(isset($_GET['type']) && $_GET['type'] != "") {
$args['tax_query'][1] = array(
'taxonomy' => 'document_type',
'field' => 'slug',
'terms' => array($_GET['type'])
);
}
// Run the query
$the_query = new WP_Query( $args );
// The Loop
if ( $the_query->have_posts() ) {
while ( $the_query->have_posts() ) {
$the_query->the_post();
the_title();
the_content();
}
} else {
echo "No results";
}
/* Restore original Post Data */
wp_reset_postdata(); ?>
Update:
I've tried the following but no luck displaying any posts.
if(isset($_GET['year']) && $_GET['year'] != "") {
$args = array(
'date_query' => array(
array(
'year' => array($_GET['year'])
),
),
);
}

Answer 1

Solved with:
if(isset($_GET['year']) && $_GET['year'] != "") {
$args = array(
'post_type' => 'policies',
'posts_per_page' => 10,
'orderby' => $sort,
'order' => $order,
's' => $s,
'date_query' => array(
array(
'year' => ($_GET['year'])
),
),
);
} else {
// default args to search by custom post type and search term
$args = array(
'post_type' => 'policies',
'posts_per_page' => 10,
'orderby' => $sort,
'order' => $order,
's' => $s
);
}