@6river/graphql-google-pubsub 中文文档教程

发布于 3年前 浏览 25 项目主页 更新于 3年前

graphql-google-pubsub

该包实现了 graphql-subscriptions 包中的 PubSubEngine 接口以及新的 AsyncIterator 接口。 它允许您将订阅管理器连接到 Google PubSub 机制以支持 多个订阅管理器实例。

Installation

npm install @axelspringer/graphql-google-pubsub 或者 yarn add @axelspringer/graphql-google-pubsub

Using as AsyncIterator

使用 Subscription 类型定义您的 GraphQL 模式:

schema {
  query: Query
  mutation: Mutation
  subscription: Subscription
}

type Subscription {
    somethingChanged: Result
}

type Result {
    id: String
}

现在,让我们创建一个简单的 GooglePubSub 实例:

import { GooglePubSub } from '@axelspringer/graphql-google-pubsub';
const pubsub = new GooglePubSub();

现在,实现您的订阅类型解析器,使用 pubsub.asyncIterator 映射您需要的事件:

const SOMETHING_CHANGED_TOPIC = 'something_changed';

export const resolvers = {
  Subscription: {
    somethingChanged: {
      subscribe: () => pubsub.asyncIterator(SOMETHING_CHANGED_TOPIC),
    },
  },
}

订阅解析器不是一个函数,而是一个带有 subscribe 方法的对象,它返回 <代码>异步迭代。

调用 GooglePubSub 实例的方法 asyncIterator 将订阅所提供的主题,并将返回绑定到 GooglePubSub 实例并监听任何事件的 AsyncIterator发表在那个话题上。 现在,GraphQL 引擎知道 somethingChanged 是一个订阅,每次我们将对这个主题使用 pubsub.publish 时,GooglePubSub 将 < code>PUBLISH 将事件发送给所有其他订阅的实例,而这些实例又会使用 GraphQL 引擎提供的 next 回调将事件发送给 GraphQL。

pubsub.publish(SOMETHING_CHANGED_TOPIC, { somethingChanged: { id: "123" }});

主题不会自动创建,必须事先创建。

如果您发布非字符串数据,它会被字符串化,您必须解析接收到的消息数据

Receive Messages

来自 Google PubSub 的收到的消息直接作为有效载荷传递给解析/过滤函数。

您可以在其中提取数据(缓冲区)或使用通用消息处理程序 来转换接收到的消息。

function commonMessageHandler ({attributes = {}, data = ''}) {
  return {
    ...attributes,
    text: data.toString()
  };
}

can use custom message handler 测试说明了通用消息处理程序的灵活性。

Dynamically use a topic based on subscription args passed on the query:

export const resolvers = {
  Subscription: {
    somethingChanged: {
      subscribe: (_, args) => pubsub.asyncIterator(`${SOMETHING_CHANGED_TOPIC}.${args.relevantId}`),
    },
  },
}

Using both arguments and payload to filter events

import { withFilter } from 'graphql-subscriptions';

export const resolvers = {
  Subscription: {
    somethingChanged: {
      subscribe: withFilter(
        (_, args) => pubsub.asyncIterator(`${SOMETHING_CHANGED_TOPIC}.${args.relevantId}`),
        (payload, variables) => payload.somethingChanged.id === variables.relevantId,
      ),
    },
  },
}

Creating the Google PubSub Client

import { GooglePubSub } from '@axelspringer/graphql-google-pubsub';

const pubSub = new GooglePubSub(options, topic2SubName, commonMessageHandler)

Options

这些是传递给内部或通过 Google PubSub 客户端的选项。 如果提供,客户端将从环境变量中提取凭据、项目名称等。 查看身份验证指南了解更多信息。 否则,您可以在选项中提供此详细信息。

const options = {
  projectId: 'project-abc',
  credentials:{
    client_email: 'client@example-email.iam.gserviceaccount.com',
    private_key: '-BEGIN PRIVATE KEY-\nsample\n-END PRIVATE KEY-\n'
  }
};

Subscription Options

订阅选项可以传入subscribe异步交互器。

注意:google.protobuf.Duration 类型必须作为对象传入具有秒属性 ({ seconds: 123 })。

const dayInSeconds = 60 * 60 * 24;

const subscriptionOptions = {
  messageRetentionDuration: { seconds: dayInSeconds },
  expirationPolicy: {
    ttl: { seconds: dayInSeconds * 2 }, // 2 Days
  },
};

await pubsub.asyncIterator("abc123", subscriptionOptions);

topic2SubName

允许构建不同的工作流程。 如果您在多个服务器实例上侦听同一个订阅,消息将在它们之间分发。 大多数时候,您希望每台服务器有不同的订阅。 这样每个服务器实例都可以通知他们的客户一条新消息。

const topic2SubName = topicName => `${topicName}-${serverName}-subscription`

commonMessageHandler

使用从 Google PubSub 接收到的消息调用公共消息处理程序。 您可以在将消息传递给订阅者的各个过滤器/解析器方法之前对其进行转换。 例如,通过这种方式可以注入 DataLoader 的一个实例,它可以在所有过滤器/解析器方法中使用。

const getDataLoader = () => new DataLoader(...);
const commonMessageHandler = ({attributes: {id}, data}) => ({id, dataLoader: getDataLoader()});
export const resolvers = {
  Subscription: {
    somethingChanged: {
      resolve: ({id, dataLoader}) => dataLoader.load(id)
    },
  },
}

Author

Jonas Hackenberg - jonas-arkulpa

Acknowledgements

这个项目的灵感主要来自 graphql-redis-subscriptions。 非常感谢其作者的工作和灵感。 感谢精益团队(Daniel VogelMartin Thomas< /a>、马塞尔·多纳尔弗洛里安·塔茨基Sebastian HerrlingerMircea Craculeac蒂姆苏萨)。

graphql-google-pubsub

This package implements the PubSubEngine Interface from the graphql-subscriptions package and also the new AsyncIterator interface. It allows you to connect your subscriptions manger to a Google PubSub mechanism to support multiple subscription manager instances.

Installation

npm install @axelspringer/graphql-google-pubsub or yarn add @axelspringer/graphql-google-pubsub

Using as AsyncIterator

Define your GraphQL schema with a Subscription type:

schema {
  query: Query
  mutation: Mutation
  subscription: Subscription
}

type Subscription {
    somethingChanged: Result
}

type Result {
    id: String
}

Now, let's create a simple GooglePubSub instance:

import { GooglePubSub } from '@axelspringer/graphql-google-pubsub';
const pubsub = new GooglePubSub();

Now, implement your Subscriptions type resolver, using the pubsub.asyncIterator to map the event you need:

const SOMETHING_CHANGED_TOPIC = 'something_changed';

export const resolvers = {
  Subscription: {
    somethingChanged: {
      subscribe: () => pubsub.asyncIterator(SOMETHING_CHANGED_TOPIC),
    },
  },
}

Subscriptions resolvers are not a function, but an object with subscribe method, that returns AsyncIterable.

Calling the method asyncIterator of the GooglePubSub instance will subscribe to the topic provided and will return an AsyncIterator binded to the GooglePubSub instance and listens to any event published on that topic. Now, the GraphQL engine knows that somethingChanged is a subscription, and every time we will use pubsub.publish over this topic, the GooglePubSub will PUBLISH the event to all other subscribed instances and those in their turn will emit the event to GraphQL using the next callback given by the GraphQL engine.

pubsub.publish(SOMETHING_CHANGED_TOPIC, { somethingChanged: { id: "123" }});

The topic doesn't get created automatically, it has to be created beforehand.

If you publish non string data it gets stringified and you have to parse the received message data.

Receive Messages

The received message from Google PubSub gets directly passed as payload to the resolve/filter function.

You might extract the data (Buffer) in there or use a common message handler to transform the received message.

function commonMessageHandler ({attributes = {}, data = ''}) {
  return {
    ...attributes,
    text: data.toString()
  };
}

The can use custom message handler test illustrates the flexibility of the common message handler.

Dynamically use a topic based on subscription args passed on the query:

export const resolvers = {
  Subscription: {
    somethingChanged: {
      subscribe: (_, args) => pubsub.asyncIterator(`${SOMETHING_CHANGED_TOPIC}.${args.relevantId}`),
    },
  },
}

Using both arguments and payload to filter events

import { withFilter } from 'graphql-subscriptions';

export const resolvers = {
  Subscription: {
    somethingChanged: {
      subscribe: withFilter(
        (_, args) => pubsub.asyncIterator(`${SOMETHING_CHANGED_TOPIC}.${args.relevantId}`),
        (payload, variables) => payload.somethingChanged.id === variables.relevantId,
      ),
    },
  },
}

Creating the Google PubSub Client

import { GooglePubSub } from '@axelspringer/graphql-google-pubsub';

const pubSub = new GooglePubSub(options, topic2SubName, commonMessageHandler)

Options

These are the options which are passed to the internal or passed Google PubSub client. The client will extract credentials, project name etc. from environment variables if provided. Have a look at the authentication guide for more information. Otherwise you can provide this details in the options.

const options = {
  projectId: 'project-abc',
  credentials:{
    client_email: 'client@example-email.iam.gserviceaccount.com',
    private_key: '-BEGIN PRIVATE KEY-\nsample\n-END PRIVATE KEY-\n'
  }
};

Subscription Options

Subscription options can be passed into subscribe or asyncInterator.

Note: google.protobuf.Duration types must be passed in as an object with a seconds property ({ seconds: 123 }).

const dayInSeconds = 60 * 60 * 24;

const subscriptionOptions = {
  messageRetentionDuration: { seconds: dayInSeconds },
  expirationPolicy: {
    ttl: { seconds: dayInSeconds * 2 }, // 2 Days
  },
};

await pubsub.asyncIterator("abc123", subscriptionOptions);

topic2SubName

Allows building different workflows. If you listen on multiple server instances to the same subscription, the messages will get distributed between them. Most of the time you want different subscriptions per server. That way every server instance can inform their clients about a new message.

const topic2SubName = topicName => `${topicName}-${serverName}-subscription`

commonMessageHandler

The common message handler gets called with the received message from Google PubSub. You can transform the message before it is passed to the individual filter/resolver methods of the subscribers. This way it is for example possible to inject one instance of a DataLoader which can be used in all filter/resolver methods.

const getDataLoader = () => new DataLoader(...);
const commonMessageHandler = ({attributes: {id}, data}) => ({id, dataLoader: getDataLoader()});
export const resolvers = {
  Subscription: {
    somethingChanged: {
      resolve: ({id, dataLoader}) => dataLoader.load(id)
    },
  },
}

Author

Jonas Hackenberg - jonas-arkulpa

Acknowledgements

This project is mostly inspired by graphql-redis-subscriptions. Many thanks to its authors for their work and inspiration. Thanks to the Lean Team (Daniel Vogel, Martin Thomas, Marcel Dohnal, Florian Tatzky, Sebastian Herrlinger, Mircea Craculeac and Tim Susa).

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