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

[Claude Heiland-Allen]

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<ckkashyap at gmail.com>  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