How do I add more than one dynamic bond while my simulation runs?

[anushkaj11]

I am trying to add dynamic bonds using the CustomWriter class.

class WriteBonds(hoomd.custom.Action):
    def __init__(self, dt):
        self.dt = dt
        self.iter = 0

    def act(self, timestep):
        print(timestep)
        snap = self._state.get_snapshot()
        snap.bonds.N = snap.bonds.N +1
        snap.bonds.group[-1] = [self.iter+1, self.iter+2]
        print("snap.bonds.group: ", snap.bonds.group)
        self._state.set_snapshot(snap) 
        self.iter = self.iter +1

I created a WriteBonds object and call it during the simulation with

    write_bonds = WriteBonds(dt)                             
    bond_writer_op = hoomd.write.CustomWriter(action=write_bonds, trigger=hoomd.trigger.Periodic(10000))
    sim.operations.writers.append(bond_writer_op) 

My issue is, I am only able to add bonds at the first trigger. I checked if my snap.bonds.group was getting updated and it seems to be getting bigger with every trigger event but I don't see more added bonds when the simulation ends.

Am I missing something here? I also tried using CustomUpdater but that doesn't seem to work to add more bonds.
I also noticed that my modifications are being written at the start - not dynamically.

UPDATE: it seems I needed to add 'topology' to dynamic in hoomd.write.GSD - I now see the kind of dynamic bonding I was looking for (Big thanks to my colleague who spotted this!)
The code above seems to be working fine.

FOLLOW-UP: I still don't know the difference between CustomWriter and CustomUpdater as it pertains to adding bonds in my code, both seem to be working just fine for adding bonds and applying forces on the new bonds

[joaander]

Writers and Updaters execute at different points during the Simulation.run loop: See https://hoomd-blue.readthedocs.io/en/v4.8.2/package-hoomd.html#hoomd.Simulation.run for details.

You should use an Updater when you modify system state and Writer when you read the system state and write results to an output (e.g. file or stream).