As noted previously (see
What ismulti-tenancy?), after converting a non-multi-tenant database to a multi-tenant database, most, if not all, of the code in an existing application will work without change. When executing against a converted multi-tenant database, all existing code that accesses database objects is implicitly tenant aware, which means that it accesses database objects that are shared (the default) or that belong to the tenancy of the connected user (if you have made any database objects multi-tenant).
Super-tenant users are allowed access to all the data in a multi-tenant database regardless of tenant ownership.
The primary requirements to run an application against a multi-tenant database is to configure one or more tenants, and to configure at least one domain per tenant to which application users can authenticate when they login to your application. For a converted multi-tenant database, any existing application only requires the default tenant in order to execute as originally designed, and you typically add additional regular tenants to expand the application to run with totally separate sets of users, again, with little or no change to the application code.
