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

posted on 2019-11-08 21:42  荣锋亮  阅读(378)  评论(0编辑  收藏  举报

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