案例:用Redis来存储关注关系
- Wang Dong - NoSQLFanRedis提供了丰富的数据类型,比起关系型数据库或者简单的Key-Value存储(比如Memcached)来,Redis的数据模型与实际应用的数据模型更相近. 比如下面说到的好友关系的存储,原作者使用了Redis的 Sets(集合)数据结构. 具体存储方式如下:对于每一个用户,其关注关系存储两份列表,一份为此用户关注的人的UID列表,另一份为此用户粉丝的UID列表,这两个列表都使用Sets(集合).
Redis提供了丰富的数据类型,比起关系型数据库或者简单的Key-Value存储(比如Memcached)来,Redis的数据模型与实际应用的数据模型更相近。比如下面说到的好友关系的存储,原作者使用了Redis的 Sets(集合)数据结构。
具体存储方式如下:对于每一个用户,其关注关系存储两份列表,一份为此用户关注的人的UID列表,另一份为此用户粉丝的UID列表,这两个列表都使用Sets(集合)。比如对于用户ID为123的用户,graph:user:123:following 保存的是其关注人的列表,graph:user:1:followed_by 保存的是关注他的人的列表。
下面是一个PHP代码的关注关系类,包括了常规的关注关系操作查询等方法,具体可看注释:
<? /* * This example would probably work best if you're using * an MVC framework, but it can be used standalone as well. * * This example also assumes you are using Predis, the excellent * PHP Redis library available here: * https://github.com/nrk/predis */ class UserNode { // The user's ID, probably loaded from MySQL private $id; // The redis server configuration private $redis_config = array( array('host' => 'localhost', 'port' => 6379 ) ); // Stores the redis connection resource so that // we only need to connect to Redis once private $redis; public function __construct($userID) { $this->id = $userID; } private function redis() { if (!$this->redis) { $this->redis = new Predis\Client($redis_config); } return $this->redis; } /* * Makes this user follow the user with the given ID. * In order to stay efficient, we need to make a two-way * directed graph. This means when we follow a user, we also * say that that user is followed by this user, making a forward * and backword directed graph. */ public function follow($user) { $this->redis()->sadd("graph:user:{$this->id}:following", $user); $this->redis()->sadd("graph:user:$user:followed_by", $this->id); } /* * Makes this user unfollow the user with the given ID. * First we check to make sure that we are actually following * the user we want to unfollow, then we remove both the forward * and backward references. */ public function unfollow($user) { if ($this->is_following()) { $this->redis()->srem("graph:user:{$this->id}:following", $user); $this->redis()->srem("graph:user:$user:followed_by", $this->id); } } /* * Returns an array of user ID's that this user follows. */ public function following() { return $this->redis()->smembers("graph:user:{$this->id}:following"); } /* * Returns an array of user ID's that this user is followed by. */ public function followed_by() { return $this->redis()->smembers("graph:user:{$this->id}:followed_by"); } /* * Test to see if this user is following the given user or not. * Returns a boolean. */ public function is_following($user) { return $this->redis()->sismember("graph:user:{$this->id}:following", $user); } /* * Test to see if this user is followed by the given user. * Returns a boolean. */ public function is_followed_by($user) { return $this->redis()->sismember("graph:user:{$this->id}:followed_by", $user); } /* * Tests to see if the relationship between this user and the given user is mutual. */ public function is_mutual($user) { return ($this->is_following($user) && $this->is_followed_by($user)); } /* * Returns the number of users that this user is following. */ public function follow_count() { return $this->redis()->scard("graph:user:{$this->id}:following"); } /* * Retuns the number of users that follow this user. */ public function follower_count() { return $this->redis()->scard("graph:user:{$this->id}:followed_by"); } /* * Finds all users that the given users follow in common. * Returns an array of user IDs */ public function common_following($users) { $redis = $this->redis(); $users[] = $this->id; $keys = array(); foreach ($users as $user) { $keys[] = "graph:user:{$user}:following"; } return call_user_func_array(array($redis, "sinter"), $keys); } /* * Finds all users that all of the given users are followed by in common. * Returns an array of user IDs */ public function common_followed_by($users) { $redis = $this->redis(); $users[] = $this->id; $keys = array(); foreach ($users as $user) { $keys[] = "graph:user:{$user}:followed_by"; } return call_user_func_array(array($redis, "sinter"), $keys); } }
下面是使用这个类来操作关注关系的例子:
<? // create two user nodes, assume for this example // they're users with no social graph entries. $user1 = UserNode(1); $user2 = UserNode(2); $user1->follows(); // array() // add some followers $user1->follow(2); $user1->follow(3); // now check the follow list $user1->follows(); // array(2, 3) // now we can also do: $user2->followed_by(); // array(1) // if we do this... $user2->follow(3); // then we can do this to see which people users #1 and #2 follow in common $user1->common_following(2); // array(3)
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