Re: [web-devel] [Yesod][Persistent] FooIdEq,FooIdIn

Hi Aur, I don't know if you have seen the previous discussions, but it looks like you are moving towards creating a SQL relational algebra library. There are 2 such existing libraries. The original is haskellDB [1], and the new one is DSH [2]. I think this is a very promising direction for Yesod, and I think there is a lot to be gained by first looking at one of the existing libraries, and seeing if at least the inner core [3] can be used with our constructor interface. I think we should at least justify why we are not re-using them. Also, I agree that it would be ideal to remove the declaration of which actions are used. There are some technical reasons for this, but at a minimum they should be justified/documented in the book. Greg Weber [1] http://hackage.haskell.org/package/haskelldb [2] http://hackage.haskell.org/package/DSH [3] http://hackage.haskell.org/package/TableAlgebra-0.1.5 On Sun, Mar 13, 2011 at 1:48 PM, Aur Saraf wrote:

Hello Michael and everyone,

I think that it is very repetitive to need to specify what actions can or cannot be done on every field.

I think it would better be made part of the FieldType, at least letting you specify defaults that can be edited in the field specification.

Also, I definitely see a need for FooIdEq as I'm toying with adding support for more complicated SQL right now.

What I have working in a toy hacked environment:

...

showQuery $ do selectAll (undefined :: Pet) -- hopefully I'll make it possible to select specific fields where_ PetTypeEq Dog -- eventually I'll probably get "PetType .== Dog" to work where_ PetOwner PersonAgeLt 12 "SELECT * FROM Pet WHERE Pet.type=? AND Person.age

I'm currently modifying the TH to support generating

...

persistFilterToJoins :: Filter val -> [(SomePersistEntity, SomePersistEntity)]

That I need in order to do this in more than a toy environment.

When there'll be something half worth showing, I'll upload to git and invite everyone to help (since this is mostly over-my-head Haskell... I've been learning a lot from it).

On Sat, Mar 12, 2011 at 8:46 PM, Michael Snoyman wrote:

...

On Sat, Mar 12, 2011 at 3:07 AM, Katsutoshi Itoh wrote:

...

Hi

I had often wanted FooIdIn, FooIdEq on Foo Persistent type. Would you support this by default?

from japan.

As Max said, glad to see that you're safe.

For FooIdEq: I don't think there is any need, since it can be expressed more succinctly with the "get" function. As for FooIdIn: this *was* a recently requested feature. Maybe we can get it in for the next release. I think it would make sense to add the In attribute to the entity itself, eg:

mkPersist [$persist| Person In name String age Int |]

Any objections?

Michael

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