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
(http://stackoverflow.com/questions/19137803/does-database-hdbc-support-named...)
* fetching multiple results returned from single statement
(http://stackoverflow.com/questions/19159287/hdbc-and-multiple-resultsets-in-...)
(in .net this is done via
http://msdn.microsoft.com/en-us/library/system.data.idatareader.nextresult.a...)
Is there any plan to get this supported in HDBI?
On Tue, Oct 15, 2013 at 7:55 PM, Alexey Uimanov
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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