From 59d56f0ae0da1d4b1898b3c7536ae38473306319 Mon Sep 17 00:00:00 2001
From: Michael Orlitzky <michael@orlitzky.com>
Date: Sat, 11 Jan 2014 18:34:26 -0500
Subject: [PATCH] Add the insert_xml_or_select function to TSN.XmlImport and
 use it in TSN.XML.News.

---
 src/TSN/XML/News.hs  | 14 +++++---------
 src/TSN/XmlImport.hs | 15 +++++++++++++++
 2 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/src/TSN/XML/News.hs b/src/TSN/XML/News.hs
index 8da4329..f962c9c 100644
--- a/src/TSN/XML/News.hs
+++ b/src/TSN/XML/News.hs
@@ -161,14 +161,11 @@ instance DbImport Message where
     -- Insert the message and acquire its primary key (unique ID)
     news_id <- insert_xml message
 
-    -- And insert each one into its own table. We use insertByAll_xml
+    -- And insert each one into its own table. We use insert_xml_or_select
     -- because we know that most teams will already exist, and we
-    -- want to get back a Left (id) for the existing team when
-    -- there's a collision. In fact, if the insert succeeds, we'll
-    -- get a Right (id) back, so we can disregard the Either
-    -- constructor entirely. That's what the (either id id) does.
-    either_nt_ids <- mapM insertByAll_xml (xml_teams message)
-    let nt_ids = map (either id id) either_nt_ids
+    -- want to get back the id for the existing team when
+    -- there's a collision.
+    nt_ids <- mapM insert_xml_or_select (xml_teams message)
 
     -- Now that the teams have been inserted, create
     -- news__news_team records mapping beween the two.
@@ -176,8 +173,7 @@ instance DbImport Message where
     mapM_ insert_ news_news_teams
 
     -- Do all of that over again for the NewsLocations.
-    either_loc_ids <- mapM insertByAll_xml (xml_locations message)
-    let loc_ids = map (either id id) either_loc_ids
+    loc_ids <- mapM insert_xml_or_select (xml_locations message)
     let news_news_locations = map (News_NewsLocation news_id) loc_ids
     mapM_ insert_ news_news_locations
 
diff --git a/src/TSN/XmlImport.hs b/src/TSN/XmlImport.hs
index 3791ab5..4300e87 100644
--- a/src/TSN/XmlImport.hs
+++ b/src/TSN/XmlImport.hs
@@ -26,3 +26,18 @@ class (FromXml a, PersistEntity (Db a)) => XmlImport a where
                   => a
                   -> m ( Either (AutoKey (Db a)) (AutoKey (Db a)) )
   insertByAll_xml x = insertByAll (from_xml x)
+
+
+  -- | Try to insert the given object and get its primary key
+  --   back. Or, if there's a unique constraint violation, get the
+  --   primary key of the unique thing already present.
+  --
+  --   Note: we can switch to using fmap here as soon as Functor is a
+  --   superclass of Monad (PersistBackend is a Monad).
+  --
+  insert_xml_or_select :: (PersistBackend m)
+                       => a
+                       -> m (AutoKey (Db a))
+  insert_xml_or_select x = do
+    tmp <- insertByAll_xml x
+    return $ (either id id) tmp
-- 
2.43.2