Django ORM and Oracle notes

Oracle and MariaDB compare a value from a JSONField as text. The filter stays correct, so a suite on SQLite passes.

A raw cursor gives back a handle, not text. The handle also reads one time only.

Above 4000 characters a key read returns an empty string, and filter() misses the row. Neither one reports a fault.

Django adds CHECK (col IS JSON). One old row of plain text stops the migration, and the error names no row.

Oracle 12.2 permits 128 characters. Django still reports 30, and the truncation is silent.

Name the state to return to, not the migration to remove. A reverse of AddField destroys the column.

Four causes, and one repair that hides a column difference until the next deploy.