plv8 require 模块试用

plv8 是postgres 的一个比较强大的插件，社区有人基于babel，browserify 实现了一个方便的require 模块加载
实际上官方也有介绍过了类似的基于数据库存储js，然后通过eval 动态加载代码，以下是一个简单的试用

环境准备

• docker-compose 文件

 

version: '3.6'

services:

  postgres:

    image: dalongrong/plv8:2.3.12

    ports:

    - "5432:5432"

    environment: 

    - "POSTGRES_PASSWORD=dalong"

  graphql-engine:

    image: hasura/graphql-engine:v1.0.0-beta.9

    ports:

    - "8080:8080"

    depends_on:

    - "postgres"

    environment:

      HASURA_GRAPHQL_DATABASE_URL: postgres://postgres:dalong@postgres:5432/postgres

      HASURA_GRAPHQL_ENABLE_CONSOLE: "true" # set to "false" to disable console

      HASURA_GRAPHQL_ENABLED_LOG_TYPES: startup, http-log, webhook-log, websocket-log, query-log

• node-plv8 项目
  package.json

 

{

  "name": "node-plv8",

  "version": "1.0.0",

  "main": "app.js",

  "bin": "app.js",

  "license": "MIT",

  "dependencies": {

    "cuid": "^2.1.6",

    "knex": "^0.20.1",

    "lodash": "^4.17.15",

    "pg": "^7.12.1",

    "plv8": "^2.1.4",

    "uuid": "^3.3.3"

  },

  "scripts": {

    "init:app": "node app"

  }

}

app.js
进行模块的注册，目前包含了lodash以及一个自己的

 

// setup plv8 connection

const PLV8 = require('plv8')

const knex = require('knex')

const knexHandle = knex({

    client: 'pg',

    connection: {

      host: "127.0.0.1",

      user: "postgres",

      password: "dalong",

      database: "postgres"

    }

  })

const plv8 = new PLV8(knexHandle)

​

// setup a log listener

plv8.on('log:error', msg => {

  console.error(msg)

})

​

// install the lodash module so that it can be loaded (via require()) later

plv8.install({modulePath:require.resolve('lodash'),moduleName:"lodash"})

  .then(() => {

​

    // eval some code

    return plv8.eval(() => {

      const _ = require('lodash')

      return _.map([ 1, 2, 3 ], e => e + 1)

    })

  })

  .then(result => {

   console.log(result)

  }).catch(err=>{

      console.log(err)

  })

    plv8.install({modulePath:require.resolve("./login"),moduleName:"login"})

  .then(() => {

    // eval some code

    return plv8.eval(() => {

      const login = require('login')

      return login

    })

  })

  .then(result => {

   console.log(result)

  }).catch(err=>{

      console.log(err)

  })

login.js 模块

module.exports = {

    name:"dalong",

    age:333

}

运行&&测试

• 启动docker 服务

docker-compose up -d

• 运行nodejs demo 服务

yarn init:app

• 效果
  目前有关于pg 通信的一些异常log，可能是和代码很就已经没维护，包版本兼容pg 的问题，后边
  调试研究下

 

yarn run v1.17.3

$ node app

(node:56198) UnhandledPromiseRejectionWarning: error: syntax error at or near ":"

    at Connection.parseE (/Users/dalong/mylearning/hasura-project/plv8/node-plv8/node_modules/pg/lib/connection.js:604:11)

    at Connection.parseMessage (/Users/dalong/mylearning/hasura-project/plv8/node-plv8/node_modules/pg/lib/connection.js:401:19)

    at Socket.<anonymous> (/Users/dalong/mylearning/hasura-project/plv8/node-plv8/node_modules/pg/lib/connection.js:121:22)

    at Socket.emit (events.js:182:13)

    at addChunk (_stream_readable.js:283:12)

    at readableAddChunk (_stream_readable.js:264:11)

    at Socket.Readable.push (_stream_readable.js:219:10)

    at TCP.onStreamRead [as onread] (internal/stream_base_commons.js:94:17)

(node:56198) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)

(node:56198) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Use async .hasTable to check if table exists and then use plain .createTable. Since .createTableIfNotExists actually just generates plain "CREATE TABLE IF NOT EXIST..." query it will not work correctly if there are any alter table queries generated for columns afterwards. To not break old migrations this function is left untouched for now, but it should not be used when writing new code and it is removed from documentation.

Use async .hasTable to check if table exists and then use plain .createTable. Since .createTableIfNotExists actually just generates plain "CREATE TABLE IF NOT EXIST..." query it will not work correctly if there are any alter table queries generated for columns afterwards. To not break old migrations this function is left untouched for now, but it should not be used when writing new code and it is removed from documentation.

{ name: 'dalong', age: 333 }

[ 2, 3, 4 ]

 

sql 方式调用

• 函数定义

CREATE or replace FUNCTION dalong2() RETURNS json AS

$$

    const login = require('login')

    return JSON.stringify(login);

$$

LANGUAGE plv8;

• 查询

SET plv8.start_proc = 'v8.plv8_init';

select * from dalong2();

 

• 效果

{"name":"dalong","age":333}

简单原理说明

node plv8 将生成的js 通过browserify 以及babel 转换，存储在v8 schema 中的modules 表中
同时注册了SET plv8.start_proc = 'v8.plv8_init'; 需要的plv8.init 函数，同时也注册了几个依赖的
函数，代码的执行通过的是eval 函数，整体上还是比较简单的，但是实现的功能确实很方便的

 

 

参考资料

https://pgxn.org/dist/plv8/doc/plv8.html
https://github.com/plv8/plv8
https://plv8.github.io/
https://github.com/rongfengliang/plv8-require-learning