composite
Composite is a group of libraries focusing on practical uses of composite records, in particular Vinyl, such as querying records from a database and converting them to JSON. These libraries are based on the excellent Frames style use of Vinyl records, though composite implements its own derived from Frames to make for a smaller dependency graph, as Frames is a full CSV parsing/printing and data manipulation library.
composite-aeson
composite-aeson provides JSON formatting facilities for records. JSON formats can be derived automatically when default formats are available, explicitly assembled, combined, or a mix. Aeson's use of FromJSON/ToJSON type classes is mostly avoided to make using JSON formats first-class while still convenient.
Example:
import qualified Data.Aeson as Aeson
import Composite.Aeson (RecJsonFormat, defaultJsonFormatRec, recFormatJson)
import Composite.Record (Record, (:->), pattern (:*:), pattern Nil)
type FId = "id" :-> Int
type FName = "name" :-> Text
type User = '[FId, FName]
userFormat :: RecJsonFormat e User
userFormat = recFormatJson defaultJsonFormatRec
alice :: Record '[User]
alice = 1 :*: "Alice" :*: Nil
aliceJson :: Aeson.Value
aliceJson = toJsonWithFormat userFormat alice
composite-base
Definitions shared by the other composite libraries or generally useful when using Vinyl/Frames records.
composite-opaleye
composite-opaleye provides the necessary instances to use a Frames record with the opaleye library, letting you use records for query expressions as well as result rows.
Example:
import Composite.Opaleye (defaultRecTable)
import Composite.Record (Record, (:->))
import Composite.TH (withLensesAndProxies)
import Control.Lens (view)
import Data.Proxy (Proxy(Proxy))
import Frames ((:->), Record, rlens)
import Opaleye (Column, PGInt8, PGText, Query, Table, (./=), asc, constant, orderBy, queryTable, restrict)
-- For each field type defined with, withLensesAndProxies will expand to the type, a record lens for the type,
-- and a proxy for the type, so for example FId is the type, fId is a lens which accesses the "id" field of any
-- record which contains that field, and fId_ is a proxy for the field type in case it's needed.
withLensesAndProxies [d|
type FId = "id" :-> Int64
type CId = "id" :-> Column PGInt8
type FName = "name" :-> Text
type CName = "name" :-> Column PGText
|]
type User = '[FId, FName]
type UserCols = '[CId, CName]
userTable :: Table (Record UserCols) (Record UserCols)
userTable = Table "users" defaultRecTable
userQuery :: Query (Record User)
userQuery =
orderBy (asc $ view cName) $ proc () -> do
user@(view cId -> recId) <- queryTable userTable -< ()
restrict -< recId ./= constant 1
returnA -< user
example
A small servant based server which uses composite-opaleye to pull records from the database, reshape
the record to an API type, and send the records out to the client as JSON via composite-aeson.
Contributing
Contributions and feedback welcome! File and issue or make a PR.
Chat
Asa (@asa) and Ross (@dridus) hang out on fpchat.