Inventory_Presser_Plugin::add_orderby_to_query( object $query )

	function add_orderby_to_query( $query )
	{
		//Do not mess with the query if it's not the main one and our CPT
		if ( ! $query->is_main_query()
			|| ! is_post_type_archive( INVP::POST_TYPE )
			|| ( empty( $_GET['orderby'] ) && empty( $this->settings['sort_vehicles_by'] ) ) )
		{
			return;
		}

		add_filter( 'posts_clauses', array( $this, 'modify_query_orderby' ) );

		/**
		 * The field we want to order by is either in $_GET['orderby'] when
		 * the user has chosen to reorder posts or saved in the plugin
		 * settings 'default-sort-key.' The sort direction is in
		 * $_GET['order'] or 'sort_vehicles_order.'
		 */
		$direction = $this->settings['sort_vehicles_order'];
		if( isset( $_GET['order'] ) )
		{
			$direction = sanitize_text_field( $_GET['order'] );
		}

		$key = $this->settings['sort_vehicles_by'];
		if( isset( $_GET['orderby'] ) )
		{
			$key = sanitize_text_field( $_GET['orderby'] );
		}

		//Make sure the meta key has the prefix
		$key = apply_filters( 'invp_prefix_meta_key', $key );
		$query->set( 'meta_key', $key );

		//maybe append to the meta_query if it is already set
		$old = $query->get( 'meta_query', array() );
		switch( apply_filters( 'invp_unprefix_meta_key', $query->query_vars['meta_key'] ) )
		{
			//make
			case 'make':
				$query->set( 'meta_query', array_merge( $old, array(
					'relation' => 'AND',
					array(
						'relation' => 'OR',
						array(
							'key'     => apply_filters( 'invp_prefix_meta_key', 'model' ),
							'compare' => 'NOT EXISTS'
						),
						array(
							'key'     => apply_filters( 'invp_prefix_meta_key', 'model' ),
							'compare' => 'EXISTS'
						),
					),
					array(
						'relation' => 'OR',
						array(
							'key'     => apply_filters( 'invp_prefix_meta_key', 'trim' ),
							'compare' => 'NOT EXISTS'
						),
						array(
							'key'     => apply_filters( 'invp_prefix_meta_key', 'trim' ),
							'compare' => 'EXISTS'
						),
					),
				) ) );
				break;

			//model
			case 'model':
				$query->set( 'meta_query', array_merge( $old, array(
						'relation' => 'AND',
						array(
							'relation' => 'OR',
							array(
								'key'     => apply_filters( 'invp_prefix_meta_key', 'model' ),
								'compare' => 'NOT EXISTS'
							),
							array(
								'key'     => apply_filters( 'invp_prefix_meta_key', 'model' ),
								'compare' => 'EXISTS'
							),
						),
						array(
							'relation' => 'OR',
							array(
								'key'     => apply_filters( 'invp_prefix_meta_key', 'trim' ),
								'compare' => 'NOT EXISTS'
							),
							array(
								'key'     => apply_filters( 'invp_prefix_meta_key', 'trim' ),
								'compare' => 'EXISTS'
							),
						),
				) ) );
				break;

			//year
			case 'year':
				$query->set( 'meta_query', array_merge( $old, array(
						'relation' => 'AND',
						array(
							'relation' => 'OR',
							array(
								'key'     => apply_filters( 'invp_prefix_meta_key', 'year' ),
								'compare' => 'NOT EXISTS'
							),
							array(
								'key'     => apply_filters( 'invp_prefix_meta_key', 'year' ),
								'compare' => 'EXISTS'
							),
						),
						array(
							'relation' => 'OR',
							array(
								'key'     => apply_filters( 'invp_prefix_meta_key', 'make' ),
								'compare' => 'NOT EXISTS'
							),
							array(
								'key'     => apply_filters( 'invp_prefix_meta_key', 'make' ),
								'compare' => 'EXISTS'
							),
						),
						array(
							'relation' => 'OR',
							array(
								'key'     => apply_filters( 'invp_prefix_meta_key', 'model' ),
								'compare' => 'NOT EXISTS'
							),
							array(
								'key'     => apply_filters( 'invp_prefix_meta_key', 'model' ),
								'compare' => 'EXISTS'
							),
						),
						array(
							'relation' => 'OR',
							array(
								'key'     => apply_filters( 'invp_prefix_meta_key', 'trim' ),
								'compare' => 'NOT EXISTS'
							),
							array(
								'key'     => apply_filters( 'invp_prefix_meta_key', 'trim' ),
								'compare' => 'EXISTS'
							),
						),
					)
				) );
				break;

			//boat fields might not exist on all vehicles, so do not require them
			case 'beam':
			case 'length':
			case 'hull_material':
				unset( $query->query_vars['meta_key'] );
				$query->set( 'meta_query', array_merge( $old, array(
						'relation' => 'OR',
						array(
							'key'     => $key,
							'compare' => 'NOT EXISTS'
						),
						array(
							'key'     => $key,
							'compare' => 'EXISTS'
						),
					)
				) );
				break;
		}

		$meta_value_or_meta_value_num = 'meta_value';
		$key_is_odometer = $key == apply_filters( 'invp_prefix_meta_key', 'odometer' );

		if( INVP::meta_value_is_number( $key ) || $key_is_odometer )
		{
			$meta_value_or_meta_value_num .= '_num';
		}

		//We also want to customize the order by to remove non-digits from the odometer
		if( $key_is_odometer )
		{
			add_filter( 'posts_orderby', array( $this, 'change_order_by_for_odometer' ), 10, 2 );
		}

		//Allow other developers to decide if the post meta values are numbers
		$query->set( 'orderby', apply_filters( 'invp_meta_value_or_meta_value_num', $meta_value_or_meta_value_num, $key ) );
		$query->set( 'order', $direction );
	}