Safe Haskell	None
Language	Haskell2010

Hyperion.Database.HasDB

Contents

General comments
Documentation

Synopsis

data DatabaseConfig = DatabaseConfig {
- dbPool :: Pool Connection
- dbProgramId :: ProgramId
- dbRetries :: Int
}
class HasDB env where
- dbConfigLens :: Lens' env DatabaseConfig
type Pool = Pool Connection
newDefaultPool :: FilePath -> IO (Pool Connection)
withConnection :: forall m env a. (MonadIO m, MonadReader env m, HasDB env) => (Connection -> IO a) -> m a
withConnectionRetry :: forall m env a. (MonadIO m, MonadReader env m, HasDB env, MonadCatch m) => (Connection -> IO a) -> m a

General comments

Hyperion.Database.HasDB provides typeclass HasDB which describes environments that contain a DatabaseConfig, which is extracted by Lens' dbConfigLens.

This is used in the following way: if we have a monad m that

is an instance of MonadIO, i.e. embeds IO actions,
an instance of MonadReader, i.e. it carries an environment,
this environment is an instance of HasDB,

then we can create m-actions using withConnection, i.e.

doStuffWithConnection :: Sql.Connection -> IO a
...
do -- here we are in m monad
  ...
  result <- withConnection doStuffWithConnection
  ...

withConnection uses Data.Pool. See withResource for details.

Documentation

data DatabaseConfig Source #

Database information datatype

Constructors

DatabaseConfig
Fields dbPool :: Pool Connection dbProgramId :: ProgramId dbRetries :: Int

Instances

Instances details

HasDB DatabaseConfig Source #
Instance details Defined in Hyperion.Database.HasDB Methods dbConfigLens :: Lens' DatabaseConfig DatabaseConfig Source #

class HasDB env where Source #

HasDB typeclass

Methods

dbConfigLens :: Lens' env DatabaseConfig Source #

Instances

Instances details

HasDB DatabaseConfig Source #
Instance details Defined in Hyperion.Database.HasDB Methods dbConfigLens :: Lens' DatabaseConfig DatabaseConfig Source #
HasDB ClusterEnv Source #	`ClusterEnv` is an instance of `HasDB` since it contains info that is sufficient to build a `DatabaseConfig`.
Instance details Defined in Hyperion.Cluster Methods dbConfigLens :: Lens' ClusterEnv DatabaseConfig Source #
HasDB JobEnv Source #	Make `JobEnv` an instance of `HasDB`.
Instance details Defined in Hyperion.Job Methods dbConfigLens :: Lens' JobEnv DatabaseConfig Source #

type Pool = Pool Connection Source #

newDefaultPool :: FilePath -> IO (Pool Connection) Source #

Produces a default pool with connections to the SQLite DB in the given file

withConnection :: forall m env a. (MonadIO m, MonadReader env m, HasDB env) => (Connection -> IO a) -> m a Source #

Extracts the connection pool from the environment of our monad, gets a connection and runs the supplied function with it

withConnectionRetry :: forall m env a. (MonadIO m, MonadReader env m, HasDB env, MonadCatch m) => (Connection -> IO a) -> m a Source #

Tries withConnection until succeeds. Failure means that SQLError is thrown during execution of the function. Otherwise execution is deemed successful. The number of attempts is determined by DatabaseConfig in the environment. If last attempt is a failure, the last exception propagates outside of withConnectionRetry. Uses retryRepeated internally.