From 9cda61694957f2f0428779319f85f626578d0cf0 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <e.dolstra@tudelft.nl>
Date: Mon, 22 Feb 2010 14:18:55 +0000
Subject: [PATCH] * The database needs a trigger to get rid of self-references
 to   prevent a foreign key constraint violation on the Refs table when  
 deleting a path.

---
 src/libstore/local-store.cc | 12 ++++++++++--
 src/libstore/schema.sql     | 10 ++++++++++
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index 0823e785bd..7df67555ee 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -109,7 +109,11 @@ struct SQLiteStmtUse
     }
     ~SQLiteStmtUse()
     {
-        stmt.reset();
+        try {
+            stmt.reset();
+        } catch (...) {
+            ignoreException();
+        }
     }
 };
 
@@ -798,6 +802,8 @@ void LocalStore::registerValidPaths(const ValidPathInfos & infos)
 void LocalStore::invalidatePath(const Path & path)
 {
     debug(format("invalidating path `%1%'") % path);
+
+    SQLiteTxn txn(db);
     
     SQLiteStmtUse use(stmtInvalidatePath);
 
@@ -807,7 +813,9 @@ void LocalStore::invalidatePath(const Path & path)
         throw SQLiteError(db, format("invalidating path `%1%' in database") % path);
 
     /* Note that the foreign key constraints on the Refs table take
-       care of deleting the references entries for `path'. */ 
+       care of deleting the references entries for `path'. */
+
+    txn.commit();
 }
 
 
diff --git a/src/libstore/schema.sql b/src/libstore/schema.sql
index 682ce5ed7b..4adad34b70 100644
--- a/src/libstore/schema.sql
+++ b/src/libstore/schema.sql
@@ -17,6 +17,16 @@ create table if not exists Refs (
 create index if not exists IndexReferrer on Refs(referrer);
 create index if not exists IndexReference on Refs(reference);
 
+-- Paths can refer to themselves, causing a tuple (N, N) in the Refs
+-- table.  This causes a deletion of the corresponding row in
+-- ValidPaths to cause a foreign key constraint violation (due to `on
+-- delete restrict' on the `reference' column).  Therefore, explicitly
+-- get rid of self-references.
+create trigger DeleteSelfRefs before delete on ValidPaths
+  begin
+    delete from Refs where referrer = old.id and reference = old.id;
+  end;
+
 create table if not exists DerivationOutputs (
     drv  integer not null,
     id   text not null, -- symbolic output id, usually "out"