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使用编程语言客户端操作 Redis

在此之前我们进行的操作都是通过 Redis 的命令行客户端 redis-cli 进行的，并没与介绍实际编程时如何操作 Redis。接下来主要会讲解如何通过具体的编程语言来操作 Redis。

Redis 支持的程序客户端

参考官方支持列表：https://redis.io/clients。

在 Node.js 中操作 Redis

Node.js 中可以操作 Redis 的软件包推荐列表：https://redis.io/clients#nodejs。 推荐下面两个：

这里我主要以 ioredis 为例。

ioredis 是功能强大的 Redis 客户端，已被世界上最大的在线商务公司阿里巴巴和许多其他了不起的公司所使用。

ioredis 特点：

基本使用

安装依赖：

Shell
npm install ioredis

npm install ioredis
js
const Redis = require("ioredis");
const redis = new Redis(); // uses defaults unless given configuration object

// ioredis supports all Redis commands:
redis.set("foo", "bar"); // returns promise which resolves to string, "OK"

// the format is: redis[SOME_REDIS_COMMAND_IN_LOWERCASE](ARGUMENTS_ARE_JOINED_INTO_COMMAND_STRING)
// the js: ` redis.set("mykey", "Hello") ` is equivalent to the cli: ` redis> SET mykey "Hello" `

// ioredis supports the node.js callback style
redis.get("foo", function (err, result) {
  if (err) {
    console.error(err);
  } else {
    console.log(result); // Promise resolves to "bar"
  }
});

// Or ioredis returns a promise if the last argument isn't a function
redis.get("foo").then(function (result) {
  console.log(result); // Prints "bar"
});

// Most responses are strings, or arrays of strings
redis.zadd("sortedSet", 1, "one", 2, "dos", 4, "quatro", 3, "three");
redis.zrange("sortedSet", 0, 2, "WITHSCORES").then((res) => console.log(res)); // Promise resolves to ["one", "1", "dos", "2", "three", "3"] as if the command was ` redis> ZRANGE sortedSet 0 2 WITHSCORES `

// All arguments are passed directly to the redis server:
redis.set("key", 100, "EX", 10);

const Redis = require("ioredis");
const redis = new Redis(); // uses defaults unless given configuration object

// ioredis supports all Redis commands:
redis.set("foo", "bar"); // returns promise which resolves to string, "OK"

// the format is: redis[SOME_REDIS_COMMAND_IN_LOWERCASE](ARGUMENTS_ARE_JOINED_INTO_COMMAND_STRING)
// the js: ` redis.set("mykey", "Hello") ` is equivalent to the cli: ` redis> SET mykey "Hello" `

// ioredis supports the node.js callback style
redis.get("foo", function (err, result) {
  if (err) {
    console.error(err);
  } else {
    console.log(result); // Promise resolves to "bar"
  }
});

// Or ioredis returns a promise if the last argument isn't a function
redis.get("foo").then(function (result) {
  console.log(result); // Prints "bar"
});

// Most responses are strings, or arrays of strings
redis.zadd("sortedSet", 1, "one", 2, "dos", 4, "quatro", 3, "three");
redis.zrange("sortedSet", 0, 2, "WITHSCORES").then((res) => console.log(res)); // Promise resolves to ["one", "1", "dos", "2", "three", "3"] as if the command was ` redis> ZRANGE sortedSet 0 2 WITHSCORES `

// All arguments are passed directly to the redis server:
redis.set("key", 100, "EX", 10);

有关更多实例，可以参考这里：https://github.com/luin/ioredis/tree/master/examples。

Pipelining

如果要发送一批命令（例如> 5），则可以使用流水线将命令在内存中排队，然后将它们一次全部发送到 Redis。这样，性能提高了50％〜300％（请参阅基准测试部分）。

redis.pipeline() 创建一个 Pipeline 实例。您可以像 Redis 实例一样在其上调用任何 Redis 命令。这些命令在内存中排队，并通过调用 exec 方法刷新到 Redis：

js
const pipeline = redis.pipeline();
pipeline.set("foo", "bar");
pipeline.del("cc");
pipeline.exec((err, results) => {
  // `err` is always null, and `results` is an array of responses
  // corresponding to the sequence of queued commands.
  // Each response follows the format `[err, result]`.
});

// You can even chain the commands:
redis
  .pipeline()
  .set("foo", "bar")
  .del("cc")
  .exec((err, results) => {});

// `exec` also returns a Promise:
const promise = redis.pipeline().set("foo", "bar").get("foo").exec();
promise.then((result) => {
  // result === [[null, 'OK'], [null, 'bar']]
});

const pipeline = redis.pipeline();
pipeline.set("foo", "bar");
pipeline.del("cc");
pipeline.exec((err, results) => {
  // `err` is always null, and `results` is an array of responses
  // corresponding to the sequence of queued commands.
  // Each response follows the format `[err, result]`.
});

// You can even chain the commands:
redis
  .pipeline()
  .set("foo", "bar")
  .del("cc")
  .exec((err, results) => {});

// `exec` also returns a Promise:
const promise = redis.pipeline().set("foo", "bar").get("foo").exec();
promise.then((result) => {
  // result === [[null, 'OK'], [null, 'bar']]
});

每个链接的命令还可以具有一个回调，该回调将在命令得到答复时被调用：

js
redis
  .pipeline()
  .set("foo", "bar")
  .get("foo", (err, result) => {
    // result === 'bar'
  })
  .exec((err, result) => {
    // result[1][1] === 'bar'
  });

redis
  .pipeline()
  .set("foo", "bar")
  .get("foo", (err, result) => {
    // result === 'bar'
  })
  .exec((err, result) => {
    // result[1][1] === 'bar'
  });

除了将命令分别添加到管道队列之外，您还可以将命令和参数数组传递给构造函数：

js
redis
  .pipeline([
    ["set", "foo", "bar"],
    ["get", "foo"],
  ])
  .exec(() => {
    /* ... */
  });

redis
  .pipeline([
    ["set", "foo", "bar"],
    ["get", "foo"],
  ])
  .exec(() => {
    /* ... */
  });

#length 属性显示管道中有多少个命令：

js
const length = redis.pipeline().set("foo", "bar").get("foo").length;
// length === 2

const length = redis.pipeline().set("foo", "bar").get("foo").length;
// length === 2

事务

大多数时候，事务命令 multi＆exec 与管道一起使用。因此，在调用 multi 时，默认情况下会自动创建 Pipeline 实例，因此您可以像使用管道一样使用 multi：

js
redis
  .multi()
  .set("foo", "bar")
  .get("foo")
  .exec((err, results) => {
    // results === [[null, 'OK'], [null, 'bar']]
  });

redis
  .multi()
  .set("foo", "bar")
  .get("foo")
  .exec((err, results) => {
    // results === [[null, 'OK'], [null, 'bar']]
  });

如果事务的命令链中存在语法错误（例如，错误的参数数量，错误的命令名称等），则不会执行任何命令，并返回错误：

js
redis
  .multi()
  .set("foo")
  .set("foo", "new value")
  .exec((err, results) => {
    // err:
    //  { [ReplyError: EXECABORT Transaction discarded because of previous errors.]
    //    name: 'ReplyError',
    //    message: 'EXECABORT Transaction discarded because of previous errors.',
    //    command: { name: 'exec', args: [] },
    //    previousErrors:
    //     [ { [ReplyError: ERR wrong number of arguments for 'set' command]
    //         name: 'ReplyError',
    //         message: 'ERR wrong number of arguments for \'set\' command',
    //         command: [Object] } ] }
  });

redis
  .multi()
  .set("foo")
  .set("foo", "new value")
  .exec((err, results) => {
    // err:
    //  { [ReplyError: EXECABORT Transaction discarded because of previous errors.]
    //    name: 'ReplyError',
    //    message: 'EXECABORT Transaction discarded because of previous errors.',
    //    command: { name: 'exec', args: [] },
    //    previousErrors:
    //     [ { [ReplyError: ERR wrong number of arguments for 'set' command]
    //         name: 'ReplyError',
    //         message: 'ERR wrong number of arguments for \'set\' command',
    //         command: [Object] } ] }
  });

就接口而言，multi 与管道的区别在于，当为每个链接的命令指定回调时，排队状态将传递给回调，而不是命令的结果：

js
redis
  .multi()
  .set("foo", "bar", (err, result) => {
    // result === 'QUEUED'
  })
  .exec(/* ... */);

redis
  .multi()
  .set("foo", "bar", (err, result) => {
    // result === 'QUEUED'
  })
  .exec(/* ... */);

如果要使用不带管道的事务，请将 { pipeline: false } 传递给 multi，每个命令将立即发送到 Redis，而无需等待 exec 调用：

js
redis.multi({ pipeline: false });
redis.set("foo", "bar");
redis.get("foo");
redis.exec((err, result) => {
  // result === [[null, 'OK'], [null, 'bar']]
});

redis.multi({ pipeline: false });
redis.set("foo", "bar");
redis.get("foo");
redis.exec((err, result) => {
  // result === [[null, 'OK'], [null, 'bar']]
});

multi 的构造函数还接受一批命令：

js
redis
  .multi([
    ["set", "foo", "bar"],
    ["get", "foo"],
  ])
  .exec(() => {
    /* ... */
  });

redis
  .multi([
    ["set", "foo", "bar"],
    ["get", "foo"],
  ])
  .exec(() => {
    /* ... */
  });

管道支持内联事务，这意味着您可以将管道中的命令子集分组为一个事务：

js
redis
  .pipeline()
  .get("foo")
  .multi()
  .set("foo", "bar")
  .get("foo")
  .exec()
  .get("foo")
  .exec();

redis
  .pipeline()
  .get("foo")
  .multi()
  .set("foo", "bar")
  .get("foo")
  .exec()
  .get("foo")
  .exec();

错误处理

Redis服务器返回的所有错误都是 ReplyError 的实例，可以通过 Redis 进行访问：

js
const Redis = require("ioredis");
const redis = new Redis();
// This command causes a reply error since the SET command requires two arguments.
redis.set("foo", (err) => {
  err instanceof Redis.ReplyError;
});

const Redis = require("ioredis");
const redis = new Redis();
// This command causes a reply error since the SET command requires two arguments.
redis.set("foo", (err) => {
  err instanceof Redis.ReplyError;
});

这是 ReplyError 的错误堆栈：

ReplyError: ERR wrong number of arguments for 'set' command
    at ReplyParser._parseResult (/app/node_modules/ioredis/lib/parsers/javascript.js:60:14)
    at ReplyParser.execute (/app/node_modules/ioredis/lib/parsers/javascript.js:178:20)
    at Socket.<anonymous> (/app/node_modules/ioredis/lib/redis/event_handler.js:99:22)
    at Socket.emit (events.js:97:17)
    at readableAddChunk (_stream_readable.js:143:16)
    at Socket.Readable.push (_stream_readable.js:106:10)
    at TCP.onread (net.js:509:20)

ReplyError: ERR wrong number of arguments for 'set' command
    at ReplyParser._parseResult (/app/node_modules/ioredis/lib/parsers/javascript.js:60:14)
    at ReplyParser.execute (/app/node_modules/ioredis/lib/parsers/javascript.js:178:20)
    at Socket.<anonymous> (/app/node_modules/ioredis/lib/redis/event_handler.js:99:22)
    at Socket.emit (events.js:97:17)
    at readableAddChunk (_stream_readable.js:143:16)
    at Socket.Readable.push (_stream_readable.js:106:10)
    at TCP.onread (net.js:509:20)

默认情况下，错误堆栈没有任何意义，因为整个堆栈都发生在 ioredis 模块本身而不是代码中。因此，要找出错误在代码中的位置并不容易。 ioredis 提供了一个选项 showFriendlyErrorStack 来解决该问题。启用 showFriendlyErrorStack 时，ioredis 将为您优化错误堆栈：

js
const Redis = require("ioredis");
const redis = new Redis({ showFriendlyErrorStack: true });
redis.set("foo");

const Redis = require("ioredis");
const redis = new Redis({ showFriendlyErrorStack: true });
redis.set("foo");

输出将是：

ReplyError: ERR wrong number of arguments for 'set' command
    at Object.<anonymous> (/app/index.js:3:7)
    at Module._compile (module.js:446:26)
    at Object.Module._extensions..js (module.js:464:10)
    at Module.load (module.js:341:32)
    at Function.Module._load (module.js:296:12)
    at Function.Module.runMain (module.js:487:10)
    at startup (node.js:111:16)
    at node.js:799:3

ReplyError: ERR wrong number of arguments for 'set' command
    at Object.<anonymous> (/app/index.js:3:7)
    at Module._compile (module.js:446:26)
    at Object.Module._extensions..js (module.js:464:10)
    at Module.load (module.js:341:32)
    at Function.Module._load (module.js:296:12)
    at Function.Module.runMain (module.js:487:10)
    at startup (node.js:111:16)
    at node.js:799:3

这次，堆栈告诉您错误发生在代码的第三行。

太好了！但是，优化错误堆栈会大大降低性能。因此，默认情况下，此选项是禁用的，只能用于调试目的。不建议在生产环境中使用此功能。

综合案例

https://github.com/attraction11/drift-bottle

Released under the MIT License.

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