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Prevent data loss when editing table with foreign keys enabled

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Our procedure for editing tables may involve a drop of the old table
definition. This will trigger the "ON DELETE CASCADE" clauses of the
child tables, leading to unexpected and silent data loss.

Following the procedure described in:
https://www.sqlite.org/lang_altertable.html
we can guarantee that no data is deleted, but at the cost of opening a
new transaction specific for the table modification. The possible pending
changes must be saved before. This is only done when the foreign_keys
pragma is enabled.

See issue #1481
This commit is contained in:
mgrojo
2018-08-07 14:32:37 +02:00
committed by Martin Kleusberg
parent 7b660338ed
commit 282e6739d9
1 changed files with 33 additions and 1 deletions
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34
src/MainWindow.cpp
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@@ -948,8 +948,40 @@ void MainWindow::editObject()
if(type == "table")
{
// For a safe and possibly complex table modification we must follow the steps documented in
// https://www.sqlite.org/lang_altertable.html
// Paragraph (first procedure): Making Other Kinds Of Table Schema Changes
QString foreign_keys = db.getPragma("foreign_keys");
if (foreign_keys == "1") {
if(db.getDirty() && QMessageBox::question(this,
QApplication::applicationName(),
tr("Editing the table requires to save all pending changes now.\nAre you sure you want to save the database?"),
QMessageBox::Save | QMessageBox::Default,
QMessageBox::Cancel | QMessageBox::Escape) != QMessageBox::Save)
return;
// Commit all changes so the foreign_keys can be effective.
fileSave();
db.setPragma("foreign_keys", "0");
}
EditTableDialog dialog(db, name, false, this);
if(dialog.exec()) {
bool ok = dialog.exec();
// If foreign_keys were enabled, we must commit or rollback the transaction so the foreign_keys pragma can be restored.
if (foreign_keys == "1") {
if (!db.executeSQL(QString("PRAGMA %1.foreign_key_check").arg(sqlb::escapeIdentifier(name.schema())))) {
QMessageBox::warning(this, QApplication::applicationName(),
tr("Error checking foreign keys after table modification. The changes will be reverted.\n"
"Message from database engine:\n%1").arg(db.lastError()));
db.revertAll();
} else {
// Commit all changes so the foreign_keys can be effective.
fileSave();
}
db.setPragma("foreign_keys", foreign_keys);
}
if(ok) {
ui->dataTable->filterHeader()->clearFilters();
populateTable();
}