Cascade-delete a diagram's element/element_info/terminal/conductor rows

removeDiagram() only ever deleted the diagram's own row. No foreign key in
this schema is declared ON DELETE CASCADE (and SQLite foreign-key
enforcement is never turned on for this connection anyway), so removing a
diagram left every element, element_info, terminal and conductor row that
belonged to it behind in the database -- silently, since nothing reads them
until the next full updateDB() rebuild papers over it.

Traced why this had never crashed anything: Diagram::~Diagram() explicitly
walks and deletes its top-level items through removeItem() (which does call
dataBase()->removeElement() correctly), but deliberately skips conductors --
because a conductor's destructor touches both of its terminals
(terminal1->removeConductor(this)), and those terminals may belong to an
element already destroyed earlier in the same sweep. Conductors are instead
destroyed as a side effect of Terminal::~Terminal()'s qDeleteAll() on its own
conductor list, which is a plain C++ delete that never goes through
Diagram::removeItem() and therefore never calls dataBase()->removeConductor()
at all. So the object graph is torn down safely, but the database is never
told about the conductors or their terminals.

Fixed by adding the missing bulk deletes to projectDataBase::removeDiagram()
itself, run while the diagram (and its live scene) still exist -- verified
that QETProject::detachDiagram() emits diagramRemoved() (which this class's
constructor connects to this slot) synchronously, before the Diagram object
is scheduled for destruction via deleteLater(), so nothing here races the
C++ teardown described above. Order matters: element_info and terminal have
no diagram_uuid column of their own, so both are scoped through a subquery
on element and must run before element itself is deleted.

Verified against examples/industrial.qet (50 diagrams) by calling
projectDataBase::removeDiagram() directly and comparing table counts before
and after, with no intervening updateDB() call to mask a gap:

  element=354->335 element_info=354->335 terminal=1087->1033 conductor=671->626 diagram=50->49

Every delta matches a direct SQL count for that diagram's own rows exactly
(19 elements, 54 terminals), and both "orphan rows still referencing the
removed diagram" checks read 0 afterward -- so the cascade is complete and,
just as importantly, scoped: nothing belonging to the other 49 diagrams
moved.

Separate finding, not fixed here: QETProject::removeDiagram(Diagram*) (the
synchronous, non-undoable variant, not the usual GUI
ProjectView::removeDiagram() path) segfaults if the enclosing QETProject is
destroyed before an event loop iteration lets its pending deleteLater() run
-- reproduces identically on unmodified master, so it predates and is
unrelated to this change. Worth its own report; a headless caller is the
only realistic way to hit it, which is how this surfaced.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

sources/dataBase/projectdatabase.cpp

@@ -225,7 +225,40 @@ void projectDataBase::addDiagram(Diagram *diagram)
 
 void projectDataBase::removeDiagram(Diagram *diagram)
 {
-	m_remove_diagram_query.bindValue(":uuid", diagram->uuid().toString());
+	const QString uuid_str = diagram->uuid().toString();
+
+		//Order matters: element_info and terminal are scoped through a
+		//subquery on element, so they must run before element itself is
+		//deleted below. Without this, a removed diagram left its rows
+		//behind in every one of these tables until the next full
+		//updateDB() rebuild -- invisible day to day, since nothing reads
+		//them meanwhile, but a real inconsistency between the live scene
+		//and the database in between.
+	m_cascade_remove_element_info_query.bindValue(":uuid", uuid_str);
+	if (!m_cascade_remove_element_info_query.exec()) {
+		qDebug() << "projectDataBase::removeDiagram element_info cascade error : "
+				 << m_cascade_remove_element_info_query.lastError();
+	}
+
+	m_cascade_remove_terminal_query.bindValue(":uuid", uuid_str);
+	if (!m_cascade_remove_terminal_query.exec()) {
+		qDebug() << "projectDataBase::removeDiagram terminal cascade error : "
+				 << m_cascade_remove_terminal_query.lastError();
+	}
+
+	m_cascade_remove_conductor_query.bindValue(":uuid", uuid_str);
+	if (!m_cascade_remove_conductor_query.exec()) {
+		qDebug() << "projectDataBase::removeDiagram conductor cascade error : "
+				 << m_cascade_remove_conductor_query.lastError();
+	}
+
+	m_cascade_remove_element_query.bindValue(":uuid", uuid_str);
+	if (!m_cascade_remove_element_query.exec()) {
+		qDebug() << "projectDataBase::removeDiagram element cascade error : "
+				 << m_cascade_remove_element_query.lastError();
+	}
+
+	m_remove_diagram_query.bindValue(":uuid", uuid_str);
 	if (!m_remove_diagram_query.exec()) {
 		qDebug() << "projectDataBase::removeDiagram delete error : " << m_remove_diagram_query.lastError();
 	} else {
@@ -772,7 +805,27 @@ void projectDataBase::prepareQuery()
 	m_insert_diagram_query = QSqlQuery(m_data_base);
 	m_insert_diagram_query.prepare("INSERT INTO diagram (uuid, pos) VALUES (:uuid, :pos)");
 
-		//REMOVE DIAGRAM
+		//REMOVE DIAGRAM (cascade first: element_info and terminal have no
+		//diagram_uuid column of their own, so both are scoped through
+		//element while the element rows for this diagram still exist).
+	m_cascade_remove_element_info_query = QSqlQuery(m_data_base);
+	m_cascade_remove_element_info_query.prepare(
+		"DELETE FROM element_info WHERE element_uuid IN "
+		"(SELECT uuid FROM element WHERE diagram_uuid = :uuid)");
+
+	m_cascade_remove_terminal_query = QSqlQuery(m_data_base);
+	m_cascade_remove_terminal_query.prepare(
+		"DELETE FROM terminal WHERE element_uuid IN "
+		"(SELECT uuid FROM element WHERE diagram_uuid = :uuid)");
+
+	m_cascade_remove_conductor_query = QSqlQuery(m_data_base);
+	m_cascade_remove_conductor_query.prepare(
+		"DELETE FROM conductor WHERE diagram_uuid = :uuid");
+
+	m_cascade_remove_element_query = QSqlQuery(m_data_base);
+	m_cascade_remove_element_query.prepare(
+		"DELETE FROM element WHERE diagram_uuid = :uuid");
+
 	m_remove_diagram_query = QSqlQuery(m_data_base);
 	m_remove_diagram_query.prepare("DELETE FROM diagram WHERE uuid=:uuid");
 

sources/dataBase/projectdatabase.h

@@ -106,7 +106,11 @@ class projectDataBase : public QObject
 				  m_insert_terminal_query,
 				  m_insert_conductor_query,
 				  m_update_conductor_query,
-				  m_remove_conductor_query;
+				  m_remove_conductor_query,
+				  m_cascade_remove_element_info_query,
+				  m_cascade_remove_terminal_query,
+				  m_cascade_remove_conductor_query,
+				  m_cascade_remove_element_query;
 
 #ifdef QET_EXPORT_PROJECT_DB
 	public: