haskelldb-users

[Haskelldb-users] General questions (insertion)

[R. J. Fernández-M. <rfe...@cs...>]

Hello!

I have a table with the following schema:

boats(bid int not null, bname string, color string)

and I would like to perform the basic insert, update, delete functions  
on it. However, I've had a hard time figuring out how to correctly  
compose HaskellDB's functions. Following some code I've seen in this  
list (and a few blogs), I wrote these little functions:

testInsert db = insert db boats ((bid << constant 1) # (bname <<  
constant "Boat") # (color << constant "Purple"))

main = do
        let db = mysqlConnect MySQLOptions { ... }
        testInsert db


Unfortunatelly, the ghc compiler tells me that neither of boats, bid,  
bname, and color are visible.

Am I missing something obvious?

Thanks for your help!

RJFM

Re: [Haskelldb-users] General questions (insertion)

[Marc W. <mar...@gm...>]

> Unfortunatelly, the ghc compiler tells me that neither of boats, bid,  
> bname, and color are visible.

I'm guessing you are missing a simple thing:
Haskelldb provides type safety when creating SQL-queries.. but how does
it know about your database scheme?
Somewhere there is a tool (src/Database/HaskellDB.hs) which can create those missing modules
"telling" haskelldb about the db scheme.

I've used this in my own project:

        dbName = "timeTracker"
        dbInfo = DBInfo dbName (DBOptions False) [ trackedData, summarize, projects ]
                  where trackedData = TInfo "trackedData" [ CInfo "tag" (StringT, False)
                                                         , CInfo "start" (CalendarTimeT, False)
                                                         , CInfo "end" (CalendarTimeT, False)
                                                         ]
                [..]

        createDBModules = dbInfoToModuleFiles "." "TimeTrackerDB" dbInfo

but there is also
        dbSpecToDatabase db dbInfo
to create the db from spec and I recall there is another method crating the
dbInfo from a real database..

Marc Weber

Re: [Haskelldb-users] General questions (insertion)

[R. J. Fernández-M. <rfe...@cs...>]

Hi!

On May 26, 2008, at 3:32 AM, Marc Weber wrote:

>>
> Haskelldb provides type safety when creating SQL-queries.. but how  
> does
> it know about your database scheme?

tiny, minor detail :) (for some reason I thought this was encapsulated  
in the connection...)

>
>        createDBModules = dbInfoToModuleFiles "." "TimeTrackerDB"  
> dbInfo
>

I used a similar construct and now have support modules, so variables  
are in scope. Hooray!

So I tested my insertion,

   testInsert database = insert database boats (bid << constant 1 #  
bname << constant "Boo" # color << constant "Purple")

only to find an unexpected error, namely, "No instance for (Num (Maybe  
Int)) arising from the literal `1' [..]

I'm sure I'm missing yet another obvious thing... any ideas?

Thanks much!

RJFM

Re: [Haskelldb-users] General questions (insertion)

[Bjorn B. <bj...@br...>]

On Mon, May 26, 2008 at 7:58 PM, "Rafael J. Fernández-Moctezuma"
<rfe...@cs...> wrote:
> Hi!
>
> On May 26, 2008, at 3:32 AM, Marc Weber wrote:
>
>>>
>> Haskelldb provides type safety when creating SQL-queries.. but how
>> does
>> it know about your database scheme?
>
> tiny, minor detail :) (for some reason I thought this was encapsulated
> in the connection...)
>
>>
>>        createDBModules = dbInfoToModuleFiles "." "TimeTrackerDB"
>> dbInfo
>>
>
> I used a similar construct and now have support modules, so variables
> are in scope. Hooray!
>
> So I tested my insertion,
>
>   testInsert database = insert database boats (bid << constant 1 #
> bname << constant "Boo" # color << constant "Purple")
>
> only to find an unexpected error, namely, "No instance for (Num (Maybe
> Int)) arising from the literal `1' [..]
>
> I'm sure I'm missing yet another obvious thing... any ideas?

Use

constant (Just 1)

instead of

constant 1

/Björn