Formulas in mysql database for rails app

Rails
1

Hello,

any ideas how I might store a formula in a mysql database and access
it through my rails application. For example, say I have a model
Formula, which has two integer variables formula.var1 and
formula.var2. And each formula should have a stored formula that is
made up of only addition and multiplication by numbers and these
variables.

I want to be able to assign formula.expression=something and
formula.evaluate=expression evaluated at current variable
assignments.

Any idea what the best way to implement this might be. I am using
MySQL 4.1.25 and Rails 2.2.2.

Thanks,
Eyal

2

From how I understand you, I think a varchar in the db storing the
expression using some sort of placeholders for the variables, then your
evaluate method would sub the vars in and use eval to evaluate the
subbed text string. You could even use erb to do the substitution if
need be. Just be careful eval’ing anything that includes user supplied
variables or expressions. Make sure you thoroughly check the variables
they supply as they could supply virtually any ruby code to be
evaluated.

HTH,
-Bill

eyal wrote:

formula.evaluate=expression evaluated at current variable
assignments.

Any idea what the best way to implement this might be. I am using
MySQL 4.1.25 and Rails 2.2.2.

Thanks,
Eyal

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