issue2551142 - Import of retired node ... unique constraint failure. Title: Import of retired node with username after active node fails with unique constraint failure. More fixes needed for mysql and postgresql. mysql: add unique constraint for (keyvalue, __retired__) when creating class in the database. On schema change if class is changed, remove the unique constraint too. upgrade version of rdbms database from 5 to 6 to add constraint to all version 5 databases that were created as version 5 and didn't get the unique constraint. Make no changes on version 5 databases upgraded from version 4, the upgrade process to 5 added the constraint. Make no changes to other databases (sqlite, postgres) during upgrade from version 5 to 6. postgres: Handle the exception raised on unique constraint violation. The exception invalidates the database connection so it can't be used to recover from the exception. Added two new database methods: checkpoint_data - performs a db.commit under postgres does nothing on other backends restore_connection_on_error - does a db.rollback on postgres, does nothing on other backends with the rollback() done on the connection I can use the database connection to fixup the import that failed on the unique constraint. This makes postgres slower but without the commit after every imported object, the rollback will delete all the entries done up to this point. Trying to figure out how to make the caller do_import batch and recover from this failure is beyond me. Also dismissed having to process the export csv file before importing. Pushing that onto a user just seems wrong. Also since import/export isn't frequently done the lack of surprise on having a failing import and reduced load/frustration for the user seems worth it. Also the import can be run in verbose mode where it prints out a row as it is processed, so it may take a while, ut the user can get feedback. db_test-base.py: add test for upgrade from 5 to 6.

--- a/roundup/backends/back_mysql.py	Mon Jun 07 10:50:45 2021 -0400
+++ b/roundup/backends/back_mysql.py	Thu Jun 10 12:52:05 2021 -0400
@@ -395,6 +395,21 @@
         # Convert all String properties to TEXT
         self._convert_string_properties()
 
+    def fix_version_5_tables(self):
+        # A bug caused the _<class>_key_retired_idx to be missing
+        # unless the database was upgraded from version 4 to 5.
+        # If it was created at version 5, the index is missing.
+        # The user class is always present and has a key.
+        # Check it for the index. If missing, add index to all
+        # classes by rerunning self.fix_version_4_tables().
+
+        # if this fails abort. Probably means no user class
+        # so we should't be doing anything.
+        if not self.sql_index_exists("_user", "_user_key_retired_idx"):
+            self.fix_version_4_tables()
+        else:
+            self.log_info('No changes needed.')
+
     def __repr__(self):
         return '<myroundsql 0x%x>'%id(self)
 
@@ -446,6 +461,10 @@
                         spec.classname, idx)
             self.sql(index_sql3)
 
+            # and the unique index for key / retired(id)
+            self.add_class_key_required_unique_constraint(spec.classname,
+                                                          spec.key)
+
         # TODO: create indexes on (selected?) Link property columns, as
         # they're more likely to be used for lookup
 
@@ -530,6 +549,12 @@
         sql = 'drop index %s on %s'%(index_name, table_name)
         self.sql(sql)
 
+        # and now the retired unique index too
+        index_name = '_%s_key_retired_idx' % cn
+        if self.sql_index_exists(table_name, index_name):
+            sql = 'drop index %s on _%s'%(index_name, cn)
+            self.sql(sql)
+
     # old-skool id generation
     def newid(self, classname):
         ''' Generate a new id for the given class