From d5b58915c065b1e8e523c2c7c2aa79732b328028 Mon Sep 17 00:00:00 2001
From: Michael Orlitzky <michael@orlitzky.com>
Date: Fri, 4 Jul 2014 01:25:12 -0400
Subject: [PATCH] Add the FromXmlFkTeams class.

---
 src/Xml.hs | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/src/Xml.hs b/src/Xml.hs
index e7d47a1..5c84664 100644
--- a/src/Xml.hs
+++ b/src/Xml.hs
@@ -7,6 +7,7 @@ module Xml (
   DtdName(..),
   FromXml(..),
   FromXmlFk(..),
+  FromXmlFkTeams(..),
   ToDb(..),
   parse_opts,
   pickle_unpickle,
@@ -36,6 +37,11 @@ import Text.XML.HXT.Core (
   xunpickleVal,
   yes )
 
+
+-- Local imports.
+import TSN.Team ( Team(..) )
+
+
 -- | Common associated type shared by 'FromXml' and 'FromXmlFk'. This
 --   basically just forces the client to define the \"database
 --   version\" of his type.
@@ -76,6 +82,22 @@ class (ToDb a) => FromXmlFk a where
   from_xml_fk :: DefaultKey (Parent a) -> a -> Db a
 
 
+-- | A further refinement of 'FromXmlFk'. These types need not only a
+--   foreign key to a parent in order to make the XML -> DB
+--   conversion, but also two foreign keys to away/home teams (as
+--   represented in "TSN.Team").
+--
+class (ToDb a) => FromXmlFkTeams a where
+  -- | The function that produces a @Db a@ out of a parent foreign
+  -- key, two team foreign keys, and an @a@. The parameter order makes
+  -- it easier to map this function over a bunch of things.
+  from_xml_fk_teams :: DefaultKey (Parent a)
+                    -> DefaultKey Team -- ^ The away team FK
+                    -> DefaultKey Team -- ^ The home team FK
+                    -> a
+                    -> Db a
+
+
 -- | Represents the DTD filename (\"SYSTEM\") part of the DOCTYPE
 --   definition.
 newtype DtdName = DtdName String
-- 
2.43.2