Thread: [Haskelldb-users] Identity columns

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Does HaskellDB support identity columns (auto-incremented integers)?
-- 
Colin Adams
Preston Lancashire

Not specifically. What are you looking for?

On Thu, Sep 17, 2009 at 2:30 AM, Colin Paul Adams
<co...@co...> wrote:
> Does HaskellDB support identity columns (auto-incremented integers)?
> --
> Colin Adams
> Preston Lancashire
>
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>>>>> "Justin" == Justin Bailey <jgb...@gm...> writes:

    Justin> Not specifically. What are you looking for? 

I want an identity column, to uniquely number the rows of a table (and
use that number within the application).

    Justin> <co...@co...> wrote:
    >> Does HaskellDB support identity columns (auto-incremented
    >> integers)? 
-- 
Colin Adams
Preston Lancashire

If you want the numbers generated in Haskell, consider the
'value-supply' library on Hackage. It allows you to create a generator
which you can pass around and which will generate a unique number for
you, on demand.

On Thu, Sep 17, 2009 at 7:45 AM, Colin Paul Adams
<co...@co...> wrote:
>>>>>> "Justin" == Justin Bailey <jgb...@gm...> writes:
>
>    Justin> Not specifically. What are you looking for?
>
> I want an identity column, to uniquely number the rows of a table (and
> use that number within the application).
>
>    Justin> <co...@co...> wrote:
>    >> Does HaskellDB support identity columns (auto-incremented
>    >> integers)?
> --
> Colin Adams
> Preston Lancashire
>

>>>>> "Justin" == Justin Bailey <jgb...@gm...> writes:

    Justin> If you want the numbers generated in Haskell, consider the
    Justin> 'value-supply' library on Hackage. It allows you to create
    Justin> a generator which you can pass around and which will
    Justin> generate a unique number for you, on demand.

I suppose that might help a little. I will only have to read the
existing maximum value from the table when restarting the application,
instead of on every insert.

    Justin> On Thu, Sep 17, 2009 at 7:45 AM, Colin Paul Adams
    Justin> <co...@co...> wrote:
    >>>>>>> "Justin" == Justin Bailey <jgb...@gm...> writes:
    >> 
    >>    Justin> Not specifically. What are you looking for?
    >> 
    >> I want an identity column, to uniquely number the rows of a
    >> table (and use that number within the application).
    >> 
    >>    Justin> <co...@co...> wrote:
    >>    >> Does HaskellDB support identity columns (auto-incremented
    >>    >> integers)?  -- Colin Adams Preston Lancashire
    >> 

-- 
Colin Adams
Preston Lancashire

In that case I would use the database driver's support for returning
auto-increment columns. You'll want to look at the specific library
you are using to see how to do that. The HaskellDB interface may hide
that from you - I'm not sure. You may want to use  HaskellDB just to
generate the appropriate SQL, which you then execute using the DB
library.

On Thu, Sep 17, 2009 at 8:05 AM, Colin Paul Adams
<co...@co...> wrote:
>>>>>> "Justin" == Justin Bailey <jgb...@gm...> writes:
>
>    Justin> If you want the numbers generated in Haskell, consider the
>    Justin> 'value-supply' library on Hackage. It allows you to create
>    Justin> a generator which you can pass around and which will
>    Justin> generate a unique number for you, on demand.
>
> I suppose that might help a little. I will only have to read the
> existing maximum value from the table when restarting the application,
> instead of on every insert.
>
>    Justin> On Thu, Sep 17, 2009 at 7:45 AM, Colin Paul Adams
>    Justin> <co...@co...> wrote:
>    >>>>>>> "Justin" == Justin Bailey <jgb...@gm...> writes:
>    >>
>    >>    Justin> Not specifically. What are you looking for?
>    >>
>    >> I want an identity column, to uniquely number the rows of a
>    >> table (and use that number within the application).
>    >>
>    >>    Justin> <co...@co...> wrote:
>    >>    >> Does HaskellDB support identity columns (auto-incremented
>    >>    >> integers)?  -- Colin Adams Preston Lancashire
>    >>
>
>
> --
> Colin Adams
> Preston Lancashire
>

>>>>> "Justin" == Justin Bailey <jgb...@gm...> writes:

    Justin> In that case I would use the database driver's support for
    Justin> returning auto-increment columns. You'll want to look at
    Justin> the specific library you are using to see how to do
    Justin> that. The HaskellDB interface may hide that from you - I'm
    Justin> not sure. You may want to use HaskellDB just to generate
    Justin> the appropriate SQL, which you then execute using the DB
    Justin> library.

This isn't going to work.

Can I get the MAX of a column using haskelldb syntax?
-- 
Colin Adams
Preston Lancashire

Sure, there is a "_max" operator which you can use:

  http://hackage.haskell.org/packages/archive/haskelldb/0.12/doc/html/Database-HaskellDB-Query.html#v%3A_max

On Thu, Sep 17, 2009 at 8:53 AM, Colin Paul Adams
<co...@co...> wrote:
>>>>>> "Justin" == Justin Bailey <jgb...@gm...> writes:
>
>    Justin> In that case I would use the database driver's support for
>    Justin> returning auto-increment columns. You'll want to look at
>    Justin> the specific library you are using to see how to do
>    Justin> that. The HaskellDB interface may hide that from you - I'm
>    Justin> not sure. You may want to use HaskellDB just to generate
>    Justin> the appropriate SQL, which you then execute using the DB
>    Justin> library.
>
> This isn't going to work.
>
> Can I get the MAX of a column using haskelldb syntax?
> --
> Colin Adams
> Preston Lancashire
>