Add the ability to get post meta from the network_postmeta table without having to switch_to_blog or jump through hoops

network_get_post_meta.php

<?php
 
/**
 *
 * Gets the post meta for a specific post from the post indexer table
 *
 * @param int|post $post    The ID of the Post that you want the meta for
 * @param string   $key     (optional) The meta key of the data you want
 * @param bool     $single  (optional) Whether to return a single Value
 * @param int|bool $blog_id The ID of the blog that the post is located on
 *
 * @return array|bool|mixed|string|void ... Whatever get_post_meta() returns normally given parameters above
 */
function network_get_post_meta( $post, $key = '', $single = false, $blog_id = false ) {
	global $wpdb;
	$meta_type = 'post';
 
	// If you didn't specify a blog ID
	if ( ! $blog_id ) {
		if ( isset( $post->BLOG_ID ) ) {
			// Well if you passed a Post resulting from network_query() then use that BLOG_ID
			$blog_id = $post->BLOG_ID;
		} else {
			// Use the Current Blog ID
			$blog_id = get_current_blog_id();
		}
	}
 
	// If you passed in a Post object, lets get the ID
	if ( is_object( $post ) ) {
		$post = $post->ID;
	}
 
	if ( ! $post = absint( $post ) ) {
		return false;
	}
 
	/**
	 * Filter whether to retrieve metadata of a specific type.
	 *
	 * The dynamic portion of the hook, $meta_type, refers to the meta
	 * object type (comment, post, or user). Returning a non-null value
	 * will effectively short-circuit the function.
	 *
	 * @since 3.1.0
	 *
	 * @param null|array|string $value     The value network_get_metadata() should
	 *                                     return - a single metadata value,
	 *                                     or an array of values.
	 * @param int               $object_id Object ID.
	 * @param string            $meta_key  Meta key.
	 * @param string|array      $single    Meta value, or an array of values.
	 */
	$check = apply_filters( "network_get_{$meta_type}_metadata", null, $post, $key, $single );
	if ( null !== $check ) {
		if ( $single && is_array( $check ) ) {
			return $check[0];
		} else {
			return $check;
		}
	}
 
	// Check Cache first
	$meta = wp_cache_get( "network_meta_{$blog_id}-{$post}", $meta_type . '_meta' );
 
	// if nothing found in cache then go to DB
	if ( ! $meta ) {
		// Query EVERYTHING based on $blog_id and $post_id
		$query = $wpdb->prepare( "SELECT meta_id, meta_key, meta_value FROM {$wpdb->base_prefix}network_postmeta WHERE blog_id = %d AND post_id = %d", $blog_id, $post );
 
		$meta = $wpdb->get_results( $query, ARRAY_A );
 
		// Now set everything in the cache for future calls (even in this request)
		wp_cache_set( "network_meta_{$blog_id}-{$post}", $meta );
	}
 
	// If there's nothing then get out
	if ( empty( $meta ) ) {
		if ( $single ) {
			return '';
		} else {
			return array();
		}
	}
 
	// You wanted Everything... here's everything
	if ( ! $key ) {
		return $meta;
	}
 
	// Now filter everything but $key
	array_filter( $meta, function ( $row ) use ( &$key ) {
		return $row['meta_key'] == $key;
	} );
	// Check to see if the key was included
	if ( ! empty( $meta ) ) {
		if ( $single ) {
			return maybe_unserialize( $meta[0]['meta_value'] );
		} else {
			return array_map( function ( $row ) {
				return maybe_unserialize( $row['meta_key'] );
			}, $meta );
		}
	} else {
		// Key isn't in meta... return the nothing stuff again per wp spec
		if ( $single ) {
			return '';
		} else {
			return array();
		}
 
	}
}