Safe Haskell | None |
---|---|
Language | Haskell2010 |
Functions to derive common boilerplate code when writing table types for the beam library. Only use them if you what you're doing.
The following GHC extensions have to be enabled in order to make the generated code typecheck:
{-# LANGUAGE TemplateHaskell, KindSignatures, StandaloneDeriving, TypeFamilies, TypeSynonymInstances, FlexibleInstances, DeriveGeneric #-}
Documentation
:: Name | The table type name. It should end with "T", otherwise the derived names will be bogus. |
-> Name | The primary key field name |
-> DecsQ |
Derives boilerplate code for beam table types.
makeTable
is equivalent to makeTable'
except that makeTable
takes a second argument,
the name of the primary key, while makeTable'
automatically makes the first field of the record
the primary key.
makeTable ''UserT 'userNumber == makeTable' ''UserT
:: Name | The table type name. It should end with "T", otherwise the derived names will be bogus. |
-> DecsQ |
Derives boilerplate code for beam table types.
>>>
:set -XTemplateHaskell
>>>
data UserT f = User { userNumber :: Columnar f Int }
>>>
putStrLn $(stringE . pprint =<< makeTable' ''UserT)
type User = UserT Data.Functor.Identity.Identity deriving instance GHC.Show.Show User instance Database.Beam.Schema.Tables.Table UserT where data Database.Beam.Schema.Tables.PrimaryKey UserT f_0 = UserId (Database.Beam.Schema.Tables.Columnar f_0 GHC.Types.Int) deriving GHC.Generics.Generic Database.Beam.Schema.Tables.primaryKey x_1 = UserId (Ghci4.userNumber x_1) type UserId (f_2 :: * -> *) = Database.Beam.Schema.Tables.PrimaryKey UserT f_2 type UserId' = UserId Data.Functor.Identity.Identity deriving instance GHC.Show.Show UserId' userNumberC :: Lens.Micro.Type.Lens' (UserT (Database.Beam.Schema.Tables.TableField UserT)) (Database.Beam.Schema.Tables.TableField UserT _) User (Database.Beam.Schema.Tables.LensFor userNumberC) = Database.Beam.Schema.Lenses.tableConfigLenses
Note: While the above example actually is a valid doctest, due to variable renaming and the pretty printer having a line break deficit it looks rather confusing. Therefore, consider the following reformatted but otherwise equivalent example:
type User = UserT Identity deriving instance Show User instance Table UserT where data PrimaryKey UserT f = UserId (Columnar f Int) deriving Generic primaryKey = UserId . userNumber type UserId f = PrimaryKey UserT f type UserId' = UserId Identity deriving instance Show UserId' userNumberC :: Lens' (UserT (TableField UserT)) (TableField UserT Int) User (LensFor userNumberC) = tableConfigLenses
Note that the UserId
type synonym is very useful when refering to other tables in fields. Consider this:
data BlogPostT f = BlogPost { blogPostId :: Columnar f Int, blogPostAuthor :: UserId f }
makeTable
is equivalent to makeTable'
except that makeTable
takes a second argument,
the name of the primary key, while makeTable'
automatically makes the first field of the record
the primary key.
makeTable ''UserT 'userNumber == makeTable' ''UserT