If an exception is generated from a method, all of the operations performed in the transaction will be automatically rolled back to the initial state. This is only applicable to a single transaction (a single RPC call). For example, imagine you are making two RPC calls to the server and there is an exception generated in the second call. This will roll back the operation that is carried out in the second RPC call. The operation performed through the first RPC call won't be rolled back. Consequently, you want to perform a complex operation through RPC. It is recommended to perform this in a single RPC call by creating a method in the model.