从字符串公式映射变量 [英] Mapping variables from a string formula

问题描述

我有一个textarea在这里用户可以创建使用下拉列表动态公式（运营商，变量等）是这样的：

I have a textarea where user can create a dynamic formulas using dropdown lists(for operators, variables etc) like this:

basic / workingDays * attendingDays

其中的值基本， workingDays ， attendingDays 保存在数据库中。我想在运行时从数据库中的这些变量映射。我怎样才能做到这一点。

where values of basic, workingDays, attendingDays are saved in database. I want to map these variable from database during runtime. How can I do this.

推荐答案

NCalc 是一个非常强大的框架，你可以试试。他们让你定义这听起来像正是你需要的动态参数。你可以做这样的事情：

NCalc is a very powerful framework that you could try. They let you define dynamic parameters which sounds like exactly what you need. You can do something like this:

var e = new Expression("basic / workingDays * attendingDays);

//Set up a custom delegate so NCalc will ask you for a parameter's value
//   when it first comes across a variable
e.EvaluateParameter += delegate(string name, ParameterArgs args)
{
   if (name == "basic")
       args.Result = GetBasicValueFromSomeWhere();
   else if (/* etc. */)
   {
       //....
   }

   //Or if the names match up you might be able to something like:
   args.Result = dataRow[name];
};

var result =  e.Evaluate();

也有一些相关的问题在那里，如这个和<一个href=\"http://stackoverflow.com/questions/4384837/is-there-a-method-that-will-evaluate-a-string-and-produce-an-integer-assuming-th\">this 之一，让一些其他的选择。

There are also some related questions out there such as this one and this one that give some other options.

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