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Your first module

Tutorial. How a module registers itself, using the ERPNext connector as the worked example. Honest scope: the entry-point mechanism is small, and the "module" boundary is still a target the code is moving toward (see the architecture page).

What "module" means here, today

fsmes info lists modules by reading the fsmes.modules entry-point group. As of 2026-09-07 one thing registers there: the ERPNext connector. The ERP factory resolves any MES_ERP_MODE it does not know built in (rest, file, off) by looking up an entry point of that name, so a connector in a separate package plugs in without a change here.

That is the whole mechanism. Quality, maintenance and scheduling are not yet separately installable packages; they ship in the kernel wheel. Turning them into entry-point modules is on the roadmap, not done.

The worked example: ERPNext

pyproject.toml:

[project.entry-points."fsmes.modules"]
erpnext = "fsmes.integrations.erp.erpnext_adapter:from_settings"

from_settings(settings) builds an adapter that satisfies the ErpAdapter protocol — three methods:

class ErpAdapter(Protocol):
    def fetch_orders(self) -> list[ProductionRequest]: ...
    def acknowledge(self, order_code: str) -> None: ...
    def send_confirmation(self, confirmation: Confirmation) -> None: ...

The models are typed (contract.py); every MES-side rule lives in services.erp, so an adapter is transport only.

Write your own connector, in its own package

  1. New package, say fsmes-sap, depending on factorysemantics-mes.
  2. Implement the three methods against fsmes.integrations.erp.contract.

  3. Register:

    [project.entry-points."fsmes.modules"]
sap = "fsmes_sap.adapter:from_settings"

  4. pip install fsmes-sap; fsmes info now lists erpnext, sap; MES_ERP_MODE=sap selects it.

Settings your connector needs come from the same MES_ environment; read them off the Settings object you are handed, or from os.environ if they are yours alone.

What to test

The ERPNext connector's tests (tests/test_erpnext.py) run against a fake ERPNext in-process: the shape to copy. Name tests after the promise they pin, not the function they call — house rule 5.

See also