[Haskell-cafe] relational data representation in memory using haskell?

[Jeremy Shaw]

At Thu, 22 May 2008 01:04:24 +0200,
Marc Weber wrote:

> Some way representing relational data which is typically stored in
> databases such as Postgresql..
> 
> Rewriting something like Postgresql in haskell would take ages..
> So I'd be satisfied with having in memory representation only (this
> would fit the HAppS state system very well .. :)

Are you familiar with the HAppS IxSet library? 

You would do something like:



$( deriveAll [''Ord,''Eq,''Read,''Show,''Default] 
   [d|
        data CD = CD AlbumTitle Artist [Track]
	newtype Artist = Artist String
	newtype AlbumTitle = AlbumTitle String
	data Track = Track TrackTitle TrackIndex 
	newtype TrackIndex = TrackIndex Int
	newtype TrackTitle = TrackTitle String
  |])

$(inferIxSet "CDS" 'noCalcs [''AlbumTitle, ''TrackTitle, ''Artist])

This creates a table with indexs on AlbumTitle, TrackTitle, and
Artist.

You can do a simple query like:

  mycds @= (Artist "Wesley Willis")

to get all the tracks by Wesley Willis.

You should be able to build joins, etc on top of that. 

j.