From Xojo Documentation
Opens the large object specified by the passed oid. The ReadOnly parameter is optional and defaults to False. If you pass True, then the large object will be opened in read-only mode. If OpenLargeObject is successful, it returns an instance of PostgreSQLLargeObject.
PostgreSQL requires that all large object operations be performed inside of a transaction. Therefore, you must start a transaction before you perform your first large object operation:
After you have performed your last large object operation, you should close the transaction, like this:
Please see the PostgreSQLLargeObject class for information on how to work with large objects.
Read the data in a large object: