Merge pull request #2061 from darko1979/issue1872

Fixes a crash after a diff operation followed by a model close action.

Author: rkhaotix

libs/libcore/src/baseobject.cpp

@@ -1630,7 +1630,11 @@ void BaseObject::clearDependencies()
 
 void BaseObject::clearReferences()
 {
-	for(auto &obj : object_refs)
+	/* Iterate over a snapshot: unsetDependency calls back into this->unsetReference
+	 * which erases from object_refs, invalidating the range-for iterator. */
+	auto refs_snapshot = object_refs;
+
+	for(auto &obj : refs_snapshot)
 		obj->unsetDependency(this);
 
 	object_refs.clear();

libs/libcore/src/databasemodel.cpp

@@ -836,10 +836,22 @@ void DatabaseModel::destroyObjects()
 	ritr = objects.rbegin();
 	ritr_end = objects.rend();
 
+	/* Pass 1: clear all deps/refs across every object before any deletion.
+	 * This prevents dangling pointers when Relationship::destroyObjects() later
+	 * frees intermediate columns/constraints that are still referenced by other objects. */
+	while(ritr != ritr_end)
+	{
+		ritr->second->clearAllDepsRefs();
+		ritr++;
+	}
+
+	ritr = objects.rbegin();
+	ritr_end = objects.rend();
+
+	/* Pass 2: now safe to delete — no object can hold live pointers to another. */
 	while(ritr != ritr_end)
 	{
 		object = ritr->second;
-		object->clearAllDepsRefs();
 		ritr++;
 
 		// We ignore the database itself, permission objects (destroyed separetely) and table children objects