I'm doing a D2D migration that requires a mapping table to map tids from the source site to the destination site. In prepareRow(), I need to check the tid for a certain vocabulary and get the corresponding tid for the destination site. For a couple reasons, this mapping table is kept in the source site. However, the problem is that the default db connection that is being used in prepareRow() is the destination db, not the source db any more, so running my query throws an error. How can I switch the connection to use the source db so I can access this table and cache it? The short term method would be to copy this table to the destination site, but this will be an ongoing migration, and I don't want to have to update the table manually in the destination site every time the table is updated.