Implementing State Machines in PostgreSQL (2017)

While this is a good approach to implements state machines, the transition function is hardwired to one transition graph. Another approach is to generalize the state and transition graph into a table, and group those transitions by a machine id, as shown here:

https://github.com/michelp/pgfsm

Now many machines (sub-graphs of state transitions) can be defined in general, and the transition checking function checks the validity of the next state based on the table, instead of static rules in a function.