Retrieve duration (in string format) from database and convert to Ruby syntax for calculation

rubyonrails-talk
1

If I store 1.month as a string in the database, how do I convert “1.month” into 1.month?

This way I can use the “1.month” value stored in database to perform the following calculation.

Time.now + 1.month

2

I don’t think this is good idea. 1.month.to_i will return in seconds as 2592000. you can store this and while fetching you can use it as it is Time.now + 2592000

3

btw you can do it using “eval” like eval(“1.month”)

4

Take a look at this gem: GitHub - josedonizetti/ruby-duration: Immutable type that represents some amount of time with accuracy in seconds. —it will convert an arbitrary duration (like 1 month, 2 weeks, etc.) into seconds which can be stored in the DB. It is very similar to what Raj is recommending, just a little more formal. Either way you can avoid eval’ing code, and your calculation can be a lot more flexible.

5

But not all months are 2592000 seconds long.....some are shorter and some are longer.... If you have a Date of 1 Jan and add 1.month to it you will get 1 Feb which is 31 days later. If you have 1 Feb and you add 1.month you will get 1 Mar which is 28 or 29 days later.

You could just store the value as x so you could do Time.now + x.month

Norm

6

If I store 1.month as a string in the database, how do I convert "1.month" into 1.month?

This way I can use the "1.month" value stored in database to perform the following calculation.

Time.now + 1.month

If you really feel you need to do this then you can store "1.month" as a string and use eval

1.9.3p194 :007 > delta = "1.month" => "1.month" 1.9.3p194 :008 > Time.now => 2013-09-22 08:52:13 +0100 1.9.3p194 :009 > Time.now + eval( delta ) => 2013-10-22 08:52:23 +0100

However if you do this be /very/ careful about what can get into the database as arbitrary code can be executed using eval and conceivably your machine could be hacked. I DO NOT recommend that you do this. If your requirement is for a delta with values such as 1 month 3 weeks and so on, then I suggest having two fields, one for the quantity and an enumerated value for the period (month, week and so on). Then work it out in code. Less efficient but /much/ safer.

Colin

7

Thanks for your help everyone.

I ended up using Chronic Duration gem.