[Haskell-cafe] Announce: HDBI-1.3 and friends
gauthier.segay at gmail.com
Wed Oct 16 10:53:47 UTC 2013
> use `runFetchAll` it will return constructed Seq with results. But I would use conduits and conduit `selectAll` http://hackage.haskell.org/package/hdbi-conduit-1.3.0/docs/Data-Conduit-HDBI.html. Conduits are realy simple and effective.
I'm unsure I expressed the question properly, multiple results (rows)
is definitely supported but multiple resultset does not seem to be.
There are occurrences where you issue multiple select statements in a
single roundtrip to the database, each select with potentially
different row layout.
After reading your answer, I actually tried (hdbc) calling the
fetchRows function several times on Statement but it won't return
anything past the first resultset.
It seems the .net NextResults() approach is good because it let's you
check whether or not there is a next resultset to fetch rows from, I
think it would be necessary to have a similar approach if this is
going to be supported.
On Wed, Oct 16, 2013 at 6:03 AM, Alexey Uimanov <s9gf4ult at gmail.com> wrote:
>> ability to use named parameters
> Yes. I dont know when It will be done, but it is on github issues already
> https://github.com/s9gf4ult/hdbi/issues/3 .
>> fetching multiple results returned from single statement
> use `runFetchAll` it will return constructed Seq with results. But I would
> use conduits and conduit `selectAll`
> Conduits are realy simple and effective.
> If you need something like nextresult just use method `fetch` of `Statement`
> until it return Nothing. It is just the same. Or use ResumableSink from
> conduits (I would).
> 2013/10/16 Gauthier Segay <gauthier.segay at gmail.com>
>> Thanks for the announcement / library, I have started using hdbc (and
>> it's odbc driver) recently and had two concerns with it so far:
>> * ability to use named parameters
>> * fetching multiple results returned from single statement
>> (in .net this is done via
>> Is there any plan to get this supported in HDBI?
>> On Tue, Oct 15, 2013 at 7:55 PM, Alexey Uimanov <s9gf4ult at gmail.com>
>> > Hello haskellers!
>> > HDBI is the fork of HDBC but reworked. It supports SQlite3 and
>> > Postgresql
>> > for now. It also supports streaming with coduits.
>> > There is TH deriving mechanism to map database rows to Haskell
>> > structures
>> > and back. HDBI is trying to become simple
>> > but still powerfull and flexible database interface. It must be suitable
>> > to
>> > become the common RDBMS interface for higher level interfaces
>> > like persistent or haskelldb.
>> > The documentation is not very good, while I have no enough time to make
>> > some.
>> > In this version changed typeclass signatures of Connection and
>> > Statement.
>> > Now methods `run` and `execute` get any instance of `ToRow` and method
>> > `fetch` return an instance of `FromRow`.
>> > Note that [SqlValue] is also an instance of `FromRow` and `ToRow`
>> > typeclasses so you do not loose the control.
>> > Methods `fromRow` and `toRow` for [SqlValue] are just `id`. SQlite and
>> > Postgresql drivers are fixed as well as hdbi-conduit.
>> > There is also new helper functions, like `onei :: Integer -> [SqlValue]`
>> > which helps you to execute queries with one parameter
>> > or execute many queries consistinf of one parameter.
>> > Prelude Database.HDBI Database.HDBI.SQlite> :set -XScopedTypeVariables
>> > Prelude Database.HDBI Database.HDBI.SQlite> :set -XOverloadedStrings
>> > Prelude Database.HDBI Database.HDBI.SQlite> c <- connectSqlite3
>> > ":memory:"
>> > Prelude Database.HDBI Database.HDBI.SQlite> runRaw c "create table
>> > test(val
>> > integer)"
>> > Prelude Database.HDBI Database.HDBI.SQlite> withTransaction c $ runMany
>> > c
>> > "insert into test(val) values (?)" $ map one [1..1000]
>> > <interactive>:7:76: Warning:
>> > Defaulting the following constraint(s) to type `Integer'
>> > .........
>> > Prelude Database.HDBI Database.HDBI.SQlite> r :: (Maybe Integer) <-
>> > runFetchOne c "select sum(val) from test" ()
>> > Prelude Database.HDBI Database.HDBI.SQlite> r
>> > Just 500500
>> > Note here that the empty set is used as a parameter of query in
>> > `runFetchOne`. Empty set is an instance of `FromRow` and `ToRow` and
>> > return
>> > an empty list of [SqlValue].
>> > Use empty list as a parameters is bad idea, because we could instantiate
>> > some another list of things, suppose the [Integer] as `FromRow` and
>> > `ToRow` instance. So it would lead to ambigous type because [SqlValue]
>> > is
>> > also a list instantiating `FromRow` and `ToRow`.
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