plv8 中使用 eval 函数执行表达式计算

在js 开发中我们都说eval 函数是邪恶的，但是此函数也有好多妙用，以下是几个简单的案例

eval 执行基于js 的表达式计算

比如我们有以下表

CREATE TABLE rules (

    id SERIAL PRIMARY KEY,

    rule_expression text

);

​

-- Indices -------------------------------------------------------

​

CREATE UNIQUE INDEX rules_pkey ON rules(id int4_ops);

• 表内容

INSERT INTO "public"."rules"("id","rule_expression")

VALUES

(1,E'"${vars_name}".length>10');

• plv8 函数

CREATE or replace FUNCTION rule_test(id int,args text) RETURNS json AS

$$

   // 解决es 模版函数问题，string 转string template

    String.prototype.interpolate = function(params) {

      const names = Object.keys(params);

      const vals = Object.values(params);

      return new Function(...names, `return \`${this}\`;`)(...vals);

    }

    var result = {}

    var plan = plv8.prepare('SELECT rule_expression from rules where id = $1',['int']);

    // only for test fetch one row 

    var rule_row = plan.execute([ id ])[0];

    let vars_name = args;

    var rule_template = rule_row.rule_expression.interpolate({vars_name});

     var execresult = eval(rule_template);

    result = {

       id: id,

       validate: execresult

    }

    plan.free();

    return JSON.stringify(result);

$$

LANGUAGE plv8;

 

 

• 调用函数

select * from rule_test(1,'ddssaa');  // return   {"id":1,"validate":false}

select * from rule_test(1,'dddaaasssssssssaa');  // return {"id":1,"validate":true}

一个比较通用的基于eval 的规则校验

• 约定
  通过vars. 进行key 的处理支持标准的js && ||
• 参考例子

 

"${vars.name}".length>10&& "${vars.version}"=="1.0"

• 函数定义

 CREATE or replace FUNCTION rule_test3(id int,args json,rule_row text) RETURNS json AS

$$

    String.prototype.interpolate = function(params) {

    const names = Object.keys(params);

    const vals = Object.values(params);

    return new Function(...names, `return \`${this}\`;`)(...vals);

  }

    var result = {}

    let vars = {...args};

    var rule_template = rule_row.interpolate({vars});

    var execresult = eval(rule_template);

    result = {

       id: id,

       validate: execresult

    }

    return JSON.stringify(result);

$$

LANGUAGE plv8;

• 调用

select a.*, rule_test3(3,'{"version":"1.0","name":"dddddddd"}',b.rule_expression) from apps a join rules b on a.id=b.id where a.id=2; /

// 2    rong    {"id":3,"validate":false}

select a.*, rule_test3(3,'{"version":"1.0","name":"dddddd1111dd"}',b.rule_expression) from apps a join rules b on a.id=b.id where a.id=2; 

// 2    rong    {"id":3,"validate":true}

 

说明

以上是一个简单的使用plv8 使用js 实现的一个简单的规则判断，核心是对于string template 的函数处理

参考资料

https://plv8.github.io/#inline-statement-calls
https://github.com/plv8/plv8