How to use formula template from db in ruby ​​on rails?

Question

Ruby on Rails

In short, there is a formula in the database, for example "PRICE * 0.07". The template is stored as text. I need this formula to work out: first, PRICE should be replaced by a number that is taken from the variable and then multiplied by 0.07. accordingly, you need to be able to write any actions (multiply, subtract, divide)

Answer 1

Solved such a problem with the help of an excellent library: https://github.com/rubysolo/dentaku
Able to parse mathematical and logical formulas, coding dynamic values ​​of variables.

Answer 2

How did you try to solve it? What are the difficulties?

Answer 3

You can write an interpreter that executes your formulas. The easiest way to do this is to master some kind of parsing library. On ruby, I used treetop and citrus, the latter will work for you.
Take a look at the example for citrus, it just parses such an interpreter of the simplest expressions.

Answer 4

some_variable = 10 
string_from_database = "some_variable * 5"

eval(string_from_database)
=> 50

The biggest problem here is to properly sanitize the string so that you don't slip some dangerous construct there.