Safe Haskell | None |
---|
This module exports a Structued
type class which can be used to
convert from Haskel "record types" to BSON
objects and vice versa.
We use Templace Haskell to provide a function deriveStructured
which can be used to automatically generate an instance of such
types for the Structured
and BSON's Val
classes.
For instance:
data User = User { userId :: Int , userFirstName :: String , userLastName :: String } deriving(Show, Read, Eq, Ord, Typeable) $(deriveStructured ''User)
deriveStrctured
used used to create the following instance of Structured
:
instance Structured User where toBSON x = [ (u "_id") := val (userId x) , (u "userFirstName") := val (userFirstName x) , (u "userLastName") := val (userLastName x) ] fromBSON doc = lookup (u "_id") doc >>= \val_1 -> lookup (u "userFirstName") doc >>= \val_2 -> lookup (u "userLastName") doc >>= \val_3 -> return User { userId = val_1 , userFirstName = val_2 , userLastname = val_3 }
To allow for structured and well-typed queies, it also generates
types corresponding to each field (which are made an instance of
Selectable
). Specifically, for the above data type, it creates:
data UserId = UserId deriving (Show, Eq) instance Selectable User UserId SObjId where s _ _ = "_id" data FirstName = FirstName deriving (Show, Eq) instance Selectable User FirstName String where s _ _ = "firstName" data LastName = LastName deriving (Show, Eq) instance Selectable User LastName String where s _ _ = "lastName"
- deriveStructured :: Name -> Q [Dec]
Documentation
deriveStructured :: Name -> Q [Dec]Source
This function generates Structured
and Val
instances for
record types.