Get post from same taxonomy.

related-widget.php

<?php

/**
 * Stoma Related Post Widget class.
 *
 * @since 1.0.0
 */
class Stomap_Related_Post_Widget extends WP_Widget {

	/**
	 * Set up the widget's unique name, ID, class, description, and other options.
	 *
	 * @since 1.0.0
	 */
	function __construct() {

		/* Set up the widget options. */
		$widget_options = array(
			'classname' => 'stomap-related-post',
			'description' => esc_html__( 'Display related professionals by category.', 'stomap' )
		);

		/* Set up the widget control options. */
		$control_options = array(
			'width' => 200,
			'height' => 350,
			'id_base' => 'stomap-related-post'
		);

		/* Create the widget. */
		$this->WP_Widget(
			'stomap-related-post',                   // $this->id_base
			__( 'Related professionals', 'stomap' ), // $this->name
			$widget_options,                         // $this->widget_options
			$control_options                         // $this->control_options
		);
	}
	
	/**
	 * Outputs the widget based on the arguments input through the widget controls.
	 *
	 * @since 1.0.0
	 */
	function widget( $args, $instance ) {
		extract( $args );
		
		/* If we are not in singular team-member page, get out of here. */
		if ( !is_singular( 'team-member' ) ) {
			return false;
		}
		
		/* Get id of the 'page'. */
		$id = get_queried_object_id();
		
		/* Id to array. */
		$id_array = array( $id );
		
		/* Get team-member-category. */
		$terms = get_the_terms( $id, 'team-member-category' );
		
		/* If page doesn't have any categories attached to it, get out of here. */
		if( empty( $terms ) ) {
			return false;
		}
		
		/* Get taxonomy IDs. */
		$term_id = array();
		
		foreach ( $terms as $term ) {
			$term_id[]  = $term->slug;
			$term_title = __( 'Other', 'stomap' ) . ' ' . $term->name;
		}

		/* Open the before widget HTML. */
		echo $before_widget;

		/* Output the term title. */
		//if ( $instance['title'] )
		echo $before_title . apply_filters( 'widget_title',  $term_title, $instance, $this->id_base ) . $after_title; 
			
		/* Set custom query to show related posts from same category. */
		$stomap_posts_args = apply_filters( 'stomap_plugin_related_post_arguments', array(
			'orderby'        => 'rand',
			'post_type'      => 'team-member',
			'tax_query' => array(
				array(
					'taxonomy' => 'team-member-category',
					'field'    => 'slug',
					'terms'    => $term_id,
				),
			),
			'post__not_in'   => $id_array, // Don't show current page
			'posts_per_page' => 5
		) );
			
		$stomap_posts = new WP_Query( $stomap_posts_args );
		?>
		
		<?php if ( $stomap_posts->have_posts() ) : ?>
		
			<?php while ( $stomap_posts->have_posts() ) : $stomap_posts->the_post(); ?>
				
				<article id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
	
					<header class="entry-header">
						<?php if ( has_post_thumbnail() ) the_post_thumbnail( 'kuorinka-large', array( 'class' => 'thumbnail-large' ) ); ?>
						<?php the_title( sprintf( '<strong><a href="%s" rel="bookmark">', esc_url( get_permalink() ) ), '</a></strong>' ); ?>
					</header><!-- .entry-header -->
		
					<div class="entry-summary" <?php hybrid_attr( 'entry-summary' ); ?>>
						<?php the_excerpt(); ?>
					</div><!-- .entry-summary -->

				</article><!-- .entry -->

			<?php endwhile; ?>

		<?php endif; wp_reset_postdata(); // reset query.
		
		/* Close the after widget HTML. */
		echo $after_widget;
	}
	
	/**
	 * Updates the widget control options for the particular instance of the widget.
	 *
	 * @since 1.0.0
	 */
	function update( $new_instance, $old_instance ) {
		$instance = $old_instance;

		/* Set the instance to the new instance. */
		$instance = $new_instance;

		/* Strip tags from elements that don't need them. */
		$instance['title'] = strip_tags( $new_instance['title'] );
		
		return $instance;
		
	}
	
	/**
	 * Displays the widget control options in the Widgets admin screen.
	 *
	 * @since 1.0.0
	 */
	function form( $instance ) {

		/* Set up the defaults. */
		$defaults = apply_filters( 'stomap_plugin_widget_defaults', array(
			'title'    => __( 'Related professionals', 'stomap' )
		) );

		$instance = wp_parse_args( (array) $instance, $defaults );
		
		?>

			<p>
				<?php echo __( 'Related professionals', 'stomap' ); ?>
			</p>
			
		<div style="clear:both;">&nbsp;</div>
	<?php
	}

}

/**
 * Register Widgets
 *
 * @since   1.0.0 
*/

function stomap_plugin_register_widgets() {
   
    register_widget( 'Stomap_Related_Post_Widget' );
 
}

add_action( 'widgets_init', 'stomap_plugin_register_widgets' );