Using HaskellDB on Tables that contain same column names

[R. Emre Başar]

Hi all,

I'm trying to create a HaskellDB application for keeping the inventory
of a set of devices. My database includes some tables which have some
columns with same names. Here is an example:

Server: id, name, vendor (fk), model(fk), system_id (always null)
Vendor: id, name
Model: id, name

I'm trying to join those three tables and create a result that contains
the names of the server, vendor and model. I use the projection:

project (Server.name << s!Server.name #
         Vendor.name << v!Vendor.name #
         Model.name << m!Model.name #
         Server.system_id << s!Server.system_id)

When I execute the query, the result contains just the name of the
servers repeated three times. When I check the generated SQL, I see that
it generates not what I expected.

Am I missing something here?

If you need, I can put the full source & generated SQL to somewhere.

--
R. Emre Başar
İstanbul Bilgi University
Department of Computer Science


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[Justin Bailey]

I'd recommend sending HaskellDB questions to the haskelldb users
mailing list. You do need to subscribe first. Now to your question:

On Sat, Oct 31, 2009 at 2:38 AM, R. Emre Başar <reb@...> wrote:
> Hi all,
> project (Server.name << s!Server.name #
>         Vendor.name << v!Vendor.name #
>         Model.name << m!Model.name #
>         Server.system_id << s!Server.system_id)
>

This is by design. Just like in SQL, the column names are not
disambiguated. If you wrote a SQL query like:

  select * from Server join Model on ... join Vendor on ...

you would get duplicate column names. You must use unique column names
in the projection. Check out the haskelldb-th package for Template
Haskell utils for easily creating column names if you don't want to
declare them by hand.

Justin
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