Re: [Haskell-cafe] DB vs read/show for persisting large data

On 14/12/11 13:59, Marc Weber wrote:

Excerpts from Michael Snoyman's message of Wed Dec 14 14:34:30 +0100 2011:

...

On Wed, Dec 14, 2011 at 3:31 PM, C K Kashyap wrote: Definite *don't* use read/show: if you make any updates to your data structures, all old files will be lost.

Well you can work around it:

data MyDataV1 = { name :: String } deriving (Read,Show)

then you make an update:

data MyDataV2 = { name :: String, age : Int } deriving (Read,Show)

then you can do let (v1 :: MyDataV1) = tryReadDataToMaybe data let (v2 :: MyDataV2) = tryReadDataToMaybe data let real_data = upgrade v1 `or` v2

But you already see that you start writing boilerplate code. It can be done for easy data structures .. But it soon will be a night mare if you have complex data.

If you use a version control system you don't loose your data - it will just be "hard to update". [snip]

I ran into this very nightmare in one project, and was recommend safecopy [0] by someone on the #haskell IRC channel. I've not (yet) used it but it looks very nice! [0] http://hackage.haskell.org/package/safecopy Claude