From f09cd01b7598c8e5fec1b9bb5b649274b88ecd35 Mon Sep 17 00:00:00 2001
From: HenningWendtland <156231187+HenningWendtland@users.noreply.github.com>
Date: Mon, 7 Sep 2026 14:20:36 +0200
Subject: [PATCH 1/7] feat(Simple Subscription): optionally add additional
 customer info

---
 simple_subscription/locale/de.po              | 65 ++++++++++++--
 simple_subscription/locale/main.pot           | 65 ++++++++++++--
 .../simple_subscription.js                    | 45 ++++++++++
 .../simple_subscription.json                  | 60 ++++++++++++-
 .../simple_subscription.py                    | 54 ++++++++++++
 .../test_simple_subscription.py               | 86 +++++++++++++++++++
 6 files changed, 358 insertions(+), 17 deletions(-)

diff --git a/simple_subscription/locale/de.po b/simple_subscription/locale/de.po
index 5872677..6a7ca67 100644
--- a/simple_subscription/locale/de.po
+++ b/simple_subscription/locale/de.po
@@ -28,6 +28,12 @@ msgstr ""
 msgid "Accounts User"
 msgstr ""
 
+#. Label of the additional_customer_data_section (Section Break) field in
+#. DocType 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Additional Customer Data"
+msgstr "Zusätzliche Kundendaten"
+
 #. Label of the amended_from (Link) field in DocType 'Simple Subscription'
 #: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
 msgid "Amended From"
@@ -38,6 +44,23 @@ msgstr ""
 msgid "Biennial"
 msgstr "Zweijährlich"
 
+#. Label of the billing_address_display (Text Editor) field in DocType
+#. 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Billing Address"
+msgstr ""
+
+#. Label of the customer_address (Link) field in DocType 'Simple
+#. Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Billing Address Name"
+msgstr ""
+
+#. Label of the contact_person (Link) field in DocType 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Billing Contact Name"
+msgstr "Name des Rechnungskontakts"
+
 #. Label of the period_type (Select) field in DocType 'Simple Subscription'
 #: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
 msgid "Billing Period is based on"
@@ -53,7 +76,13 @@ msgstr "Rechnungszeit"
 msgid "Company"
 msgstr "Unternehmen"
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js:28
+#. Label of the contact_display (Small Text) field in DocType 'Simple
+#. Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Contact"
+msgstr ""
+
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js:73
 msgid "Create current {0} invoice"
 msgstr "Aktuelle {0} Rechnung erstellen"
 
@@ -89,7 +118,7 @@ msgstr ""
 msgid "Disabled"
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:135
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:195
 msgid "Failed to create subscription invoice"
 msgstr "Fehler beim Erstellen der Abo-Rechnung"
 
@@ -129,15 +158,21 @@ msgstr ""
 msgid "Monthly"
 msgstr "Monatlich"
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:57
+#. Description of the 'Additional Customer Data' (Section Break) field in
+#. DocType 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Optional. If empty, defaults are set on invoice generation"
+msgstr "Optional. Wenn leer, werden bei der Rechnungserstellung die Standardwerte gesetzt."
+
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:107
 msgid "Please amend Subscription {0} before creating a Sales Invoice."
 msgstr "Bitte ändern Sie das Abo {0} bevor Sie eine Rechnung erstellen."
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:51
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:101
 msgid "Please enable Subscription {0} before creating a Sales Invoice."
 msgstr "Bitte aktivieren Sie das Abo {0} bevor Sie eine Rechnung erstellen."
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:54
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:104
 msgid "Please submit Subscription {0} before creating a Sales Invoice."
 msgstr "Bitte buchen Sie das Abo {0} bevor Sie eine Rechnung erstellen."
 
@@ -151,7 +186,7 @@ msgstr ""
 msgid "Quarterly"
 msgstr "Vierteljährlich"
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:124
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:184
 msgid "Sales Invoice already exists for this period: {}"
 msgstr "Rechnung für diese Periode existiert bereits: {}"
 
@@ -160,6 +195,18 @@ msgstr "Rechnung für diese Periode existiert bereits: {}"
 msgid "Selling"
 msgstr ""
 
+#. Label of the shipping_address_display (Text Editor) field in DocType
+#. 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Shipping Address"
+msgstr ""
+
+#. Label of the shipping_address_name (Link) field in DocType 'Simple
+#. Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Shipping Address Name"
+msgstr ""
+
 #. Name of a DocType
 #. Label of a Link in the Simple Subscription Selling Workspace
 #. Label of a shortcut in the Simple Subscription Selling Workspace
@@ -184,8 +231,7 @@ msgstr "Vertrieb"
 msgid "Start Date"
 msgstr "Startdatum"
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:209
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:221
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:271
 msgid "Start Date is required for frequency {0}."
 msgstr "Startdatum ist für die Frequenz {0} erforderlich."
 
@@ -233,3 +279,6 @@ msgstr "Kalendermonate"
 msgid "start date"
 msgstr "Startdatum"
 
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:90
+msgid "{0} {1} does not belong to Customer {2}."
+msgstr "{0} {1} gehört nicht zu Kunde {2}."
diff --git a/simple_subscription/locale/main.pot b/simple_subscription/locale/main.pot
index a8c2ac1..3d6e406 100644
--- a/simple_subscription/locale/main.pot
+++ b/simple_subscription/locale/main.pot
@@ -26,6 +26,12 @@ msgstr ""
 msgid "Accounts User"
 msgstr ""
 
+#. Label of the additional_customer_data_section (Section Break) field in
+#. DocType 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Additional Customer Data"
+msgstr ""
+
 #. Label of the amended_from (Link) field in DocType 'Simple Subscription'
 #: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
 msgid "Amended From"
@@ -36,6 +42,23 @@ msgstr ""
 msgid "Biennial"
 msgstr ""
 
+#. Label of the billing_address_display (Text Editor) field in DocType
+#. 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Billing Address"
+msgstr ""
+
+#. Label of the customer_address (Link) field in DocType 'Simple
+#. Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Billing Address Name"
+msgstr ""
+
+#. Label of the contact_person (Link) field in DocType 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Billing Contact Name"
+msgstr ""
+
 #. Label of the period_type (Select) field in DocType 'Simple Subscription'
 #: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
 msgid "Billing Period is based on"
@@ -51,7 +74,13 @@ msgstr ""
 msgid "Company"
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js:28
+#. Label of the contact_display (Small Text) field in DocType 'Simple
+#. Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Contact"
+msgstr ""
+
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js:73
 msgid "Create current {0} invoice"
 msgstr ""
 
@@ -87,7 +116,7 @@ msgstr ""
 msgid "Disabled"
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:135
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:195
 msgid "Failed to create subscription invoice"
 msgstr ""
 
@@ -127,15 +156,21 @@ msgstr ""
 msgid "Monthly"
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:57
+#. Description of the 'Additional Customer Data' (Section Break) field in
+#. DocType 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Optional. If empty, defaults are set on invoice generation"
+msgstr ""
+
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:107
 msgid "Please amend Subscription {0} before creating a Sales Invoice."
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:51
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:101
 msgid "Please enable Subscription {0} before creating a Sales Invoice."
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:54
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:104
 msgid "Please submit Subscription {0} before creating a Sales Invoice."
 msgstr ""
 
@@ -149,7 +184,7 @@ msgstr ""
 msgid "Quarterly"
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:124
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:184
 msgid "Sales Invoice already exists for this period: {}"
 msgstr ""
 
@@ -158,6 +193,18 @@ msgstr ""
 msgid "Selling"
 msgstr ""
 
+#. Label of the shipping_address_display (Text Editor) field in DocType
+#. 'Simple Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Shipping Address"
+msgstr ""
+
+#. Label of the shipping_address_name (Link) field in DocType 'Simple
+#. Subscription'
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+msgid "Shipping Address Name"
+msgstr ""
+
 #. Name of a DocType
 #. Label of a Link in the Simple Subscription Selling Workspace
 #. Label of a shortcut in the Simple Subscription Selling Workspace
@@ -182,8 +229,7 @@ msgstr ""
 msgid "Start Date"
 msgstr ""
 
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:209
-#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:221
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:271
 msgid "Start Date is required for frequency {0}."
 msgstr ""
 
@@ -231,3 +277,6 @@ msgstr ""
 msgid "start date"
 msgstr ""
 
+#: simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py:90
+msgid "{0} {1} does not belong to Customer {2}."
+msgstr ""
diff --git a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js
index 9f89807..d76df45 100644
--- a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js
+++ b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js
@@ -1,8 +1,25 @@
 // Copyright (c) 2022, ALYF GmbH and contributors
 // For license information, please see license.txt
 
+function customer_link_query(frm, query) {
+	return {
+		query: query,
+		filters: { link_doctype: "Customer", link_name: frm.doc.customer },
+	};
+}
+
 frappe.ui.form.on("Simple Subscription", {
 	setup: function (frm) {
+		for (const field of ["customer_address", "shipping_address_name"]) {
+			frm.set_query(field, () =>
+				customer_link_query(frm, "frappe.contacts.doctype.address.address.address_query")
+			);
+		}
+
+		frm.set_query("contact_person", () =>
+			customer_link_query(frm, "frappe.contacts.doctype.contact.contact.contact_query")
+		);
+
 		frm.set_query("item", "items", function () {
 			return {
 				filters: {
@@ -21,6 +38,34 @@ frappe.ui.form.on("Simple Subscription", {
 		});
 	},
 
+	customer: function (frm) {
+		// address and contact are customer specific, don't keep the previous customer's
+		for (const field of ["customer_address", "shipping_address_name", "contact_person"]) {
+			frm.set_value(field, null);
+		}
+	},
+
+	customer_address: function (frm) {
+		erpnext.utils.get_address_display(frm, "customer_address", "billing_address_display");
+	},
+
+	shipping_address_name: function (frm) {
+		erpnext.utils.get_address_display(frm, "shipping_address_name", "shipping_address_display");
+	},
+
+	contact_person: function (frm) {
+		if (!frm.doc.contact_person) {
+			frm.set_value("contact_display", "");
+			return;
+		}
+
+		frappe.call({
+			method: "frappe.contacts.doctype.contact.contact.get_contact_details",
+			args: { contact: frm.doc.contact_person },
+			callback: (r) => r.message && frm.set_value("contact_display", r.message.contact_display),
+		});
+	},
+
 	refresh: function (frm) {
 		if (frm.doc.docstatus !== 1 || frm.doc.disabled === 1) return;
 
diff --git a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
index 4c0d406..8c06744 100644
--- a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+++ b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
@@ -17,6 +17,14 @@
   "billing_time",
   "frequency",
   "disabled",
+  "additional_customer_data_section",
+  "customer_address",
+  "billing_address_display",
+  "shipping_address_name",
+  "shipping_address_display",
+  "column_break_beul",
+  "contact_person",
+  "contact_display",
   "section_break_5",
   "items",
   "section_break_7",
@@ -125,6 +133,56 @@
    "label": "Currency",
    "options": "Currency",
    "reqd": 1
+  },
+  {
+   "collapsible": 1,
+   "description": "Optional. If empty, defaults are set on invoice generation",
+   "fieldname": "additional_customer_data_section",
+   "fieldtype": "Section Break",
+   "label": "Additional Customer Data"
+  },
+  {
+   "fieldname": "customer_address",
+   "fieldtype": "Link",
+   "label": "Billing Address Name",
+   "options": "Address"
+  },
+  {
+   "fieldname": "billing_address_display",
+   "fieldtype": "Text Editor",
+   "is_virtual": 1,
+   "label": "Billing Address",
+   "read_only": 1
+  },
+  {
+   "fieldname": "shipping_address_name",
+   "fieldtype": "Link",
+   "label": "Shipping Address Name",
+   "options": "Address"
+  },
+  {
+   "fieldname": "shipping_address_display",
+   "fieldtype": "Text Editor",
+   "is_virtual": 1,
+   "label": "Shipping Address",
+   "read_only": 1
+  },
+  {
+   "fieldname": "column_break_beul",
+   "fieldtype": "Column Break"
+  },
+  {
+   "fieldname": "contact_person",
+   "fieldtype": "Link",
+   "label": "Billing Contact Name",
+   "options": "Contact"
+  },
+  {
+   "fieldname": "contact_display",
+   "fieldtype": "Small Text",
+   "is_virtual": 1,
+   "label": "Contact",
+   "read_only": 1
   }
  ],
  "is_submittable": 1,
@@ -134,7 +192,7 @@
    "link_fieldname": "simple_subscription"
   }
  ],
- "modified": "2026-06-15 11:53:49.870013",
+ "modified": "2026-09-07 12:41:55.374840",
  "modified_by": "Administrator",
  "module": "Simple Subscription",
  "name": "Simple Subscription",
diff --git a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py
index 8571c7f..acac47d 100644
--- a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py
+++ b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py
@@ -8,6 +8,8 @@
 from erpnext.accounts.doctype.sales_invoice.sales_invoice import SalesInvoice
 from erpnext.accounts.party import get_party_details
 from frappe import _
+from frappe.contacts.doctype.address.address import get_address_display
+from frappe.contacts.doctype.contact.contact import get_contact_details
 from frappe.model.document import Document
 from frappe.utils import today
 
@@ -41,9 +43,56 @@ class BillingTime(Enum):
 	AfterEndOfPeriod = "after end of period"
 
 
+# forwarded to the Sales Invoice, which uses the same fieldnames
+CUSTOMER_LINK_FIELDS: dict[str, str] = {
+	"customer_address": "Address",
+	"shipping_address_name": "Address",
+	"contact_person": "Contact",
+}
+
+
 class SimpleSubscription(Document):
+	@property
+	def billing_address_display(self) -> str | None:
+		return get_address_display(self.customer_address)
+
+	@property
+	def shipping_address_display(self) -> str | None:
+		return get_address_display(self.shipping_address_name)
+
+	@property
+	def contact_display(self) -> str | None:
+		if not self.contact_person:
+			return None
+		return frappe.db.get_value("Contact", self.contact_person, "full_name")
+
 	def validate(self):
 		validate_calendar_frequencies(self.period_type, self.frequency, self.start_date)
+		self.validate_customer_links()
+
+	def validate_customer_links(self) -> None:
+		"""The .js queries filter by customer, but the customer can change afterwards."""
+		for fieldname, doctype in CUSTOMER_LINK_FIELDS.items():
+			name = self.get(fieldname)
+			if not name:
+				continue
+
+			if not frappe.db.exists(
+				"Dynamic Link",
+				{
+					"parenttype": doctype,
+					"parent": name,
+					"link_doctype": "Customer",
+					"link_name": self.customer,
+				},
+			):
+				frappe.throw(
+					_("{0} {1} does not belong to Customer {2}.").format(
+						_(self.meta.get_label(fieldname)),
+						frappe.bold(name),
+						frappe.bold(self.customer),
+					)
+				)
 
 	def create_invoice(self, from_date: date, to_date: date) -> SalesInvoice:
 		msg = None
@@ -62,6 +111,8 @@ def create_invoice(self, from_date: date, to_date: date) -> SalesInvoice:
 		invoice = frappe.new_doc("Sales Invoice")
 		invoice.company = self.company
 		invoice.customer = self.customer
+		invoice.customer_address = self.customer_address
+		invoice.shipping_address_name = self.shipping_address_name
 		invoice.selling_price_list = self.get_price_list()
 		for row in self.items:
 			invoice.append(
@@ -76,6 +127,9 @@ def create_invoice(self, from_date: date, to_date: date) -> SalesInvoice:
 		invoice.to_date = to_date
 		invoice.simple_subscription = self.name
 		invoice.set_missing_values()
+		if self.contact_person:
+			# set_missing_values() would have filled in the customer's primary contact instead
+			invoice.update(get_contact_details(self.contact_person))
 		return invoice.insert()
 
 	def get_price_list(self) -> str | None:
diff --git a/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py b/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py
index efa1d60..d3e670a 100644
--- a/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py
+++ b/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py
@@ -5,6 +5,7 @@
 from datetime import date
 
 import frappe
+from frappe.tests import IntegrationTestCase
 
 from .simple_subscription import (
 	BillingTime,
@@ -196,3 +197,88 @@ def test_get_from_and_to_date(self):
 		)
 		self.assertEqual(from_date, date(2020, 1, 1))
 		self.assertEqual(to_date, date(2021, 12, 31))
+
+
+class TestSubscriptionCustomerData(IntegrationTestCase):
+	"""Address/Contact prefill: customer-bound validation and forwarding to the invoice."""
+
+	@classmethod
+	def setUpClass(cls):
+		super().setUpClass()
+		cls.customer = frappe.get_doc(doctype="Customer", customer_name="_Test Sub Customer").insert()
+		cls.other_customer = frappe.get_doc(
+			doctype="Customer", customer_name="_Test Sub Other Customer"
+		).insert()
+		cls.address = make_address("_Test Sub Billing", cls.customer.name, "Rechnungsweg 1")
+		cls.shipping_address = make_address("_Test Sub Shipping", cls.customer.name, "Lieferweg 2")
+		cls.other_address = make_address("_Test Sub Foreign", cls.other_customer.name, "Fremdweg 3")
+		cls.contact = make_contact("_Test Sub Contact", cls.customer.name)
+
+	def make_subscription(self, **kwargs):
+		return frappe.get_doc(
+			doctype="Simple Subscription",
+			company="_Test Company",
+			customer=self.customer.name,
+			start_date="2024-01-01",
+			frequency="Yearly",
+			items=[{"item": "_Test Item", "qty": 1}],
+			**kwargs,
+		)
+
+	def test_rejects_address_of_another_customer(self):
+		subscription = self.make_subscription(customer_address=self.other_address)
+		self.assertRaises(frappe.ValidationError, subscription.insert)
+
+	def test_virtual_fields_render_linked_records(self):
+		subscription = self.make_subscription(
+			customer_address=self.address,
+			shipping_address_name=self.shipping_address,
+			contact_person=self.contact,
+		).insert()
+
+		self.assertIn("Rechnungsweg 1", subscription.billing_address_display)
+		self.assertIn("Lieferweg 2", subscription.shipping_address_display)
+		self.assertEqual(subscription.contact_display, "_Test Sub Contact")
+
+	def test_forwards_links_to_invoice(self):
+		subscription = self.make_subscription(
+			customer_address=self.address,
+			shipping_address_name=self.shipping_address,
+			contact_person=self.contact,
+		).insert()
+		subscription.submit()
+
+		invoice = subscription.create_invoice(date(2024, 1, 1), date(2024, 12, 31))
+
+		self.assertIn(invoice.customer_address, (self.address, self.shipping_address))
+		self.assertEqual(invoice.shipping_address_name, self.shipping_address)
+		self.assertEqual(invoice.contact_person, self.contact)
+		self.assertEqual(invoice.contact_display, "_Test Sub Contact")
+
+	def test_invoice_falls_back_to_customer_defaults(self):
+		subscription = self.make_subscription().insert()
+		subscription.submit()
+
+		invoice = subscription.create_invoice(date(2024, 1, 1), date(2024, 12, 31))
+
+		self.assertIn(invoice.customer_address, (self.address, self.shipping_address))
+
+
+def make_address(title: str, customer: str, line1: str) -> str:
+	return frappe.get_doc(
+		doctype="Address",
+		address_title=title,
+		address_type="Billing",
+		address_line1=line1,
+		city="Berlin",
+		country="Germany",
+		links=[{"link_doctype": "Customer", "link_name": customer}],
+	).insert().name
+
+
+def make_contact(first_name: str, customer: str) -> str:
+	return frappe.get_doc(
+		doctype="Contact",
+		first_name=first_name,
+		links=[{"link_doctype": "Customer", "link_name": customer}],
+	).insert().name

From 87fb4b095320762bd2fa1f44c7048e21cc340647 Mon Sep 17 00:00:00 2001
From: HenningWendtland <156231187+HenningWendtland@users.noreply.github.com>
Date: Mon, 7 Sep 2026 14:26:00 +0200
Subject: [PATCH 2/7] fix: set allow_on_submit for new link fields

---
 .../doctype/simple_subscription/simple_subscription.json     | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
index 8c06744..c089041 100644
--- a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
+++ b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.json
@@ -142,6 +142,7 @@
    "label": "Additional Customer Data"
   },
   {
+   "allow_on_submit": 1,
    "fieldname": "customer_address",
    "fieldtype": "Link",
    "label": "Billing Address Name",
@@ -155,6 +156,7 @@
    "read_only": 1
   },
   {
+   "allow_on_submit": 1,
    "fieldname": "shipping_address_name",
    "fieldtype": "Link",
    "label": "Shipping Address Name",
@@ -172,6 +174,7 @@
    "fieldtype": "Column Break"
   },
   {
+   "allow_on_submit": 1,
    "fieldname": "contact_person",
    "fieldtype": "Link",
    "label": "Billing Contact Name",
@@ -192,7 +195,7 @@
    "link_fieldname": "simple_subscription"
   }
  ],
- "modified": "2026-09-07 12:41:55.374840",
+ "modified": "2026-09-07 14:24:50.615780",
  "modified_by": "Administrator",
  "module": "Simple Subscription",
  "name": "Simple Subscription",

From b75054ad92147b9c8b4c32add369b7296940b946 Mon Sep 17 00:00:00 2001
From: HenningWendtland <156231187+HenningWendtland@users.noreply.github.com>
Date: Mon, 7 Sep 2026 17:25:32 +0200
Subject: [PATCH 3/7] fix: add on_update_after_submit validation

---
 .../doctype/simple_subscription/simple_subscription.py         | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py
index acac47d..8682130 100644
--- a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py
+++ b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.py
@@ -70,6 +70,9 @@ def validate(self):
 		validate_calendar_frequencies(self.period_type, self.frequency, self.start_date)
 		self.validate_customer_links()
 
+	def before_update_after_submit(self):
+		self.validate_customer_links()
+
 	def validate_customer_links(self) -> None:
 		"""The .js queries filter by customer, but the customer can change afterwards."""
 		for fieldname, doctype in CUSTOMER_LINK_FIELDS.items():

From 5494f0a91b5ff9cc1e4a19cc556c2b6f9feb4629 Mon Sep 17 00:00:00 2001
From: HenningWendtland <156231187+HenningWendtland@users.noreply.github.com>
Date: Mon, 7 Sep 2026 17:26:07 +0200
Subject: [PATCH 4/7] fix: make tests not depend on erpnext

---
 .../test_simple_subscription.py               | 146 ++++++++++++++----
 1 file changed, 112 insertions(+), 34 deletions(-)

diff --git a/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py b/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py
index d3e670a..54be686 100644
--- a/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py
+++ b/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py
@@ -5,7 +5,6 @@
 from datetime import date
 
 import frappe
-from frappe.tests import IntegrationTestCase
 
 from .simple_subscription import (
 	BillingTime,
@@ -199,35 +198,63 @@ def test_get_from_and_to_date(self):
 		self.assertEqual(to_date, date(2021, 12, 31))
 
 
-class TestSubscriptionCustomerData(IntegrationTestCase):
-	"""Address/Contact prefill: customer-bound validation and forwarding to the invoice."""
+class TestSubscriptionCustomerData(unittest.TestCase):
+	"""Address/Contact prefill: customer-bound validation and forwarding to the invoice.
+
+	Deliberately a plain TestCase: frappe.tests.IntegrationTestCase would resolve the test
+	record dependencies of Simple Subscription, which pulls in ERPNext's whole object graph
+	(including every Company test record) and breaks on a fresh site. Everything needed here
+	is created below instead.
+	"""
 
 	@classmethod
 	def setUpClass(cls):
 		super().setUpClass()
-		cls.customer = frappe.get_doc(doctype="Customer", customer_name="_Test Sub Customer").insert()
-		cls.other_customer = frappe.get_doc(
-			doctype="Customer", customer_name="_Test Sub Other Customer"
-		).insert()
-		cls.address = make_address("_Test Sub Billing", cls.customer.name, "Rechnungsweg 1")
-		cls.shipping_address = make_address("_Test Sub Shipping", cls.customer.name, "Lieferweg 2")
-		cls.other_address = make_address("_Test Sub Foreign", cls.other_customer.name, "Fremdweg 3")
-		cls.contact = make_contact("_Test Sub Contact", cls.customer.name)
+		cls.currency = frappe.defaults.get_global_default("currency")
+		cls.company = make_company(cls.currency)
+		cls.item = make_item()
+		cls.customer = make_customer("_Test Sub Customer")
+		cls.other_customer = make_customer("_Test Sub Other Customer")
+		cls.address = make_address("_Test Sub Billing", cls.customer, "Rechnungsweg 1", primary=True)
+		cls.shipping_address = make_address("_Test Sub Shipping", cls.customer, "Lieferweg 2", shipping=True)
+		cls.other_address = make_address("_Test Sub Foreign", cls.other_customer, "Fremdweg 3")
+		cls.contact = make_contact("_Test Sub Contact", cls.customer)
+		cls.other_contact = make_contact("_Test Sub Foreign Contact", cls.other_customer)
+		frappe.db.commit()
+
+	def tearDown(self):
+		frappe.db.rollback()
 
 	def make_subscription(self, **kwargs):
 		return frappe.get_doc(
 			doctype="Simple Subscription",
-			company="_Test Company",
-			customer=self.customer.name,
+			company=self.company,
+			customer=self.customer,
+			currency=self.currency,
 			start_date="2024-01-01",
 			frequency="Yearly",
-			items=[{"item": "_Test Item", "qty": 1}],
+			items=[{"item": self.item, "qty": 1}],
 			**kwargs,
 		)
 
-	def test_rejects_address_of_another_customer(self):
-		subscription = self.make_subscription(customer_address=self.other_address)
-		self.assertRaises(frappe.ValidationError, subscription.insert)
+	def test_rejects_links_of_another_customer(self):
+		for fieldname, value in (
+			("customer_address", self.other_address),
+			("shipping_address_name", self.other_address),
+			("contact_person", self.other_contact),
+		):
+			with self.subTest(fieldname=fieldname):
+				subscription = self.make_subscription(**{fieldname: value})
+				self.assertRaises(frappe.ValidationError, subscription.insert)
+
+	def test_rejects_links_still_stale_after_submit(self):
+		"""The links are allow_on_submit, so validate() no longer guards them."""
+		subscription = self.make_subscription(customer_address=self.address).insert()
+		subscription.submit()
+
+		subscription.customer_address = self.other_address
+		# must be the ownership check, not the generic "cannot change after submit" guard
+		self.assertRaisesRegex(frappe.ValidationError, "does not belong to Customer", subscription.save)
 
 	def test_virtual_fields_render_linked_records(self):
 		subscription = self.make_subscription(
@@ -240,6 +267,13 @@ def test_virtual_fields_render_linked_records(self):
 		self.assertIn("Lieferweg 2", subscription.shipping_address_display)
 		self.assertEqual(subscription.contact_display, "_Test Sub Contact")
 
+	def test_virtual_fields_are_empty_without_links(self):
+		subscription = self.make_subscription().insert()
+
+		self.assertIsNone(subscription.billing_address_display)
+		self.assertIsNone(subscription.shipping_address_display)
+		self.assertIsNone(subscription.contact_display)
+
 	def test_forwards_links_to_invoice(self):
 		subscription = self.make_subscription(
 			customer_address=self.address,
@@ -250,9 +284,10 @@ def test_forwards_links_to_invoice(self):
 
 		invoice = subscription.create_invoice(date(2024, 1, 1), date(2024, 12, 31))
 
-		self.assertIn(invoice.customer_address, (self.address, self.shipping_address))
+		self.assertEqual(invoice.customer_address, self.address)
 		self.assertEqual(invoice.shipping_address_name, self.shipping_address)
 		self.assertEqual(invoice.contact_person, self.contact)
+		# the whole contact block must come from the chosen contact, not the customer default
 		self.assertEqual(invoice.contact_display, "_Test Sub Contact")
 
 	def test_invoice_falls_back_to_customer_defaults(self):
@@ -261,24 +296,67 @@ def test_invoice_falls_back_to_customer_defaults(self):
 
 		invoice = subscription.create_invoice(date(2024, 1, 1), date(2024, 12, 31))
 
-		self.assertIn(invoice.customer_address, (self.address, self.shipping_address))
+		self.assertEqual(invoice.customer_address, self.address)
+		self.assertEqual(invoice.shipping_address_name, self.shipping_address)
 
 
-def make_address(title: str, customer: str, line1: str) -> str:
-	return frappe.get_doc(
-		doctype="Address",
-		address_title=title,
-		address_type="Billing",
-		address_line1=line1,
-		city="Berlin",
-		country="Germany",
-		links=[{"link_doctype": "Customer", "link_name": customer}],
-	).insert().name
+def make_company(currency: str) -> str:
+	"""A company in the site's own currency, so the invoice does not trip the party-account check."""
+	name = "_Test Sub Company"
+	if not frappe.db.exists("Company", name):
+		frappe.get_doc(
+			doctype="Company",
+			company_name=name,
+			abbr="_TSC",
+			default_currency=currency,
+			country="Germany",
+		).insert()
+	return name
+
+
+def make_item() -> str:
+	name = "_Test Sub Item"
+	if not frappe.db.exists("Item", name):
+		frappe.get_doc(
+			doctype="Item",
+			item_code=name,
+			item_group="All Item Groups",
+			stock_uom="Nos",
+			is_stock_item=0,
+			is_sales_item=1,
+		).insert()
+	return name
+
+
+def make_customer(name: str) -> str:
+	if not frappe.db.exists("Customer", name):
+		frappe.get_doc(doctype="Customer", customer_name=name).insert()
+	return name
+
+
+def make_address(title: str, customer: str, line1: str, primary=False, shipping=False) -> str:
+	name = f"{title}-Billing"
+	if not frappe.db.exists("Address", name):
+		frappe.get_doc(
+			doctype="Address",
+			address_title=title,
+			address_type="Billing",
+			address_line1=line1,
+			city="Berlin",
+			country="Germany",
+			is_primary_address=int(primary),
+			is_shipping_address=int(shipping),
+			links=[{"link_doctype": "Customer", "link_name": customer}],
+		).insert()
+	return name
 
 
 def make_contact(first_name: str, customer: str) -> str:
-	return frappe.get_doc(
-		doctype="Contact",
-		first_name=first_name,
-		links=[{"link_doctype": "Customer", "link_name": customer}],
-	).insert().name
+	name = f"{first_name}-{customer}"
+	if not frappe.db.exists("Contact", name):
+		frappe.get_doc(
+			doctype="Contact",
+			first_name=first_name,
+			links=[{"link_doctype": "Customer", "link_name": customer}],
+		).insert()
+	return name

From 26ad94e32829c3e33e0b5548cc5655ad915f8ce8 Mon Sep 17 00:00:00 2001
From: HenningWendtland <156231187+HenningWendtland@users.noreply.github.com>
Date: Mon, 7 Sep 2026 17:27:44 +0200
Subject: [PATCH 5/7] fix: catch the edge case where the contact changes, while
 the contact_display is fetched

---
 .../simple_subscription/simple_subscription.js        | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js
index d76df45..e7603db 100644
--- a/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js
+++ b/simple_subscription/simple_subscription/doctype/simple_subscription/simple_subscription.js
@@ -54,15 +54,20 @@ frappe.ui.form.on("Simple Subscription", {
 	},
 
 	contact_person: function (frm) {
-		if (!frm.doc.contact_person) {
+		const contact = frm.doc.contact_person;
+		if (!contact) {
 			frm.set_value("contact_display", "");
 			return;
 		}
 
 		frappe.call({
 			method: "frappe.contacts.doctype.contact.contact.get_contact_details",
-			args: { contact: frm.doc.contact_person },
-			callback: (r) => r.message && frm.set_value("contact_display", r.message.contact_display),
+			args: { contact },
+			callback: (r) =>
+				// the selection may have moved on while the call was in flight
+				r.message &&
+				frm.doc.contact_person === contact &&
+				frm.set_value("contact_display", r.message.contact_display),
 		});
 	},
 

From 141172db4fcde76c2b522d43b8467587b2398c75 Mon Sep 17 00:00:00 2001
From: HenningWendtland <156231187+HenningWendtland@users.noreply.github.com>
Date: Tue, 8 Sep 2026 12:52:24 +0200
Subject: [PATCH 6/7] fix: simplify test cases

---
 .../test_simple_subscription.py               | 153 +++++++-----------
 1 file changed, 60 insertions(+), 93 deletions(-)

diff --git a/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py b/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py
index 54be686..2890c99 100644
--- a/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py
+++ b/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py
@@ -10,6 +10,7 @@
 	BillingTime,
 	Frequency,
 	PeriodType,
+	SimpleSubscription,
 	get_calendar_period,
 	get_date_period,
 	get_from_and_to_date,
@@ -199,43 +200,56 @@ def test_get_from_and_to_date(self):
 
 
 class TestSubscriptionCustomerData(unittest.TestCase):
-	"""Address/Contact prefill: customer-bound validation and forwarding to the invoice.
+	"""Customer-bound Address/Contact links: the ownership check and the display properties.
 
-	Deliberately a plain TestCase: frappe.tests.IntegrationTestCase would resolve the test
-	record dependencies of Simple Subscription, which pulls in ERPNext's whole object graph
-	(including every Company test record) and breaks on a fresh site. Everything needed here
-	is created below instead.
+	Kept deliberately light. Anything that inserts a Simple Subscription needs a Company and an
+	Item, and anything that generates the invoice needs a fully set-up ERPNext site -- fixtures
+	that only the setup wizard creates and that CI (a bare `install-app erpnext`) does not have.
+	So these exercise the app's own logic on an in-memory document; that the invoice picks the
+	links up is ERPNext's `_get_party_details` doing its normal job.
 	"""
 
 	@classmethod
 	def setUpClass(cls):
 		super().setUpClass()
-		cls.currency = frappe.defaults.get_global_default("currency")
-		cls.company = make_company(cls.currency)
-		cls.item = make_item()
 		cls.customer = make_customer("_Test Sub Customer")
 		cls.other_customer = make_customer("_Test Sub Other Customer")
-		cls.address = make_address("_Test Sub Billing", cls.customer, "Rechnungsweg 1", primary=True)
-		cls.shipping_address = make_address("_Test Sub Shipping", cls.customer, "Lieferweg 2", shipping=True)
+		cls.address = make_address("_Test Sub Billing", cls.customer, "Rechnungsweg 1")
 		cls.other_address = make_address("_Test Sub Foreign", cls.other_customer, "Fremdweg 3")
 		cls.contact = make_contact("_Test Sub Contact", cls.customer)
 		cls.other_contact = make_contact("_Test Sub Foreign Contact", cls.other_customer)
 		frappe.db.commit()
 
-	def tearDown(self):
-		frappe.db.rollback()
+	@classmethod
+	def tearDownClass(cls):
+		for doctype, name in (
+			("Contact", cls.contact),
+			("Contact", cls.other_contact),
+			("Address", cls.address),
+			("Address", cls.other_address),
+			("Customer", cls.customer),
+			("Customer", cls.other_customer),
+		):
+			frappe.delete_doc(doctype, name, force=True, ignore_missing=True)
+		frappe.db.commit()
+		super().tearDownClass()
 
 	def make_subscription(self, **kwargs):
-		return frappe.get_doc(
-			doctype="Simple Subscription",
-			company=self.company,
-			customer=self.customer,
-			currency=self.currency,
-			start_date="2024-01-01",
-			frequency="Yearly",
-			items=[{"item": self.item, "qty": 1}],
-			**kwargs,
+		subscription = frappe.new_doc("Simple Subscription")
+		subscription.customer = self.customer
+		subscription.update(kwargs)
+		return subscription
+
+	def test_accepts_links_of_the_same_customer(self):
+		subscription = self.make_subscription(
+			customer_address=self.address,
+			shipping_address_name=self.address,
+			contact_person=self.contact,
 		)
+		subscription.validate_customer_links()  # must not raise
+
+	def test_accepts_empty_links(self):
+		self.make_subscription().validate_customer_links()  # must not raise
 
 	def test_rejects_links_of_another_customer(self):
 		for fieldname, value in (
@@ -245,88 +259,43 @@ def test_rejects_links_of_another_customer(self):
 		):
 			with self.subTest(fieldname=fieldname):
 				subscription = self.make_subscription(**{fieldname: value})
-				self.assertRaises(frappe.ValidationError, subscription.insert)
-
-	def test_rejects_links_still_stale_after_submit(self):
-		"""The links are allow_on_submit, so validate() no longer guards them."""
-		subscription = self.make_subscription(customer_address=self.address).insert()
-		subscription.submit()
-
-		subscription.customer_address = self.other_address
-		# must be the ownership check, not the generic "cannot change after submit" guard
-		self.assertRaisesRegex(frappe.ValidationError, "does not belong to Customer", subscription.save)
+				self.assertRaisesRegex(
+					frappe.ValidationError,
+					"does not belong to Customer",
+					subscription.validate_customer_links,
+				)
+
+	def test_guards_the_links_after_submit_too(self):
+		"""The fields are allow_on_submit, and validate() does not run on update after submit."""
+		self.assertTrue(
+			hasattr(SimpleSubscription, "before_update_after_submit"),
+			"allow_on_submit links need a before_update_after_submit guard",
+		)
+		subscription = self.make_subscription(customer_address=self.other_address)
+		self.assertRaisesRegex(
+			frappe.ValidationError,
+			"does not belong to Customer",
+			subscription.before_update_after_submit,
+		)
 
-	def test_virtual_fields_render_linked_records(self):
+	def test_display_properties_render_linked_records(self):
 		subscription = self.make_subscription(
 			customer_address=self.address,
-			shipping_address_name=self.shipping_address,
+			shipping_address_name=self.address,
 			contact_person=self.contact,
-		).insert()
+		)
 
 		self.assertIn("Rechnungsweg 1", subscription.billing_address_display)
-		self.assertIn("Lieferweg 2", subscription.shipping_address_display)
+		self.assertIn("Rechnungsweg 1", subscription.shipping_address_display)
 		self.assertEqual(subscription.contact_display, "_Test Sub Contact")
 
-	def test_virtual_fields_are_empty_without_links(self):
-		subscription = self.make_subscription().insert()
+	def test_display_properties_are_empty_without_links(self):
+		subscription = self.make_subscription()
 
 		self.assertIsNone(subscription.billing_address_display)
 		self.assertIsNone(subscription.shipping_address_display)
 		self.assertIsNone(subscription.contact_display)
 
-	def test_forwards_links_to_invoice(self):
-		subscription = self.make_subscription(
-			customer_address=self.address,
-			shipping_address_name=self.shipping_address,
-			contact_person=self.contact,
-		).insert()
-		subscription.submit()
-
-		invoice = subscription.create_invoice(date(2024, 1, 1), date(2024, 12, 31))
-
-		self.assertEqual(invoice.customer_address, self.address)
-		self.assertEqual(invoice.shipping_address_name, self.shipping_address)
-		self.assertEqual(invoice.contact_person, self.contact)
-		# the whole contact block must come from the chosen contact, not the customer default
-		self.assertEqual(invoice.contact_display, "_Test Sub Contact")
-
-	def test_invoice_falls_back_to_customer_defaults(self):
-		subscription = self.make_subscription().insert()
-		subscription.submit()
-
-		invoice = subscription.create_invoice(date(2024, 1, 1), date(2024, 12, 31))
-
-		self.assertEqual(invoice.customer_address, self.address)
-		self.assertEqual(invoice.shipping_address_name, self.shipping_address)
-
-
-def make_company(currency: str) -> str:
-	"""A company in the site's own currency, so the invoice does not trip the party-account check."""
-	name = "_Test Sub Company"
-	if not frappe.db.exists("Company", name):
-		frappe.get_doc(
-			doctype="Company",
-			company_name=name,
-			abbr="_TSC",
-			default_currency=currency,
-			country="Germany",
-		).insert()
-	return name
-
-
-def make_item() -> str:
-	name = "_Test Sub Item"
-	if not frappe.db.exists("Item", name):
-		frappe.get_doc(
-			doctype="Item",
-			item_code=name,
-			item_group="All Item Groups",
-			stock_uom="Nos",
-			is_stock_item=0,
-			is_sales_item=1,
-		).insert()
-	return name
-
 
 def make_customer(name: str) -> str:
 	if not frappe.db.exists("Customer", name):
@@ -334,7 +303,7 @@ def make_customer(name: str) -> str:
 	return name
 
 
-def make_address(title: str, customer: str, line1: str, primary=False, shipping=False) -> str:
+def make_address(title: str, customer: str, line1: str) -> str:
 	name = f"{title}-Billing"
 	if not frappe.db.exists("Address", name):
 		frappe.get_doc(
@@ -344,8 +313,6 @@ def make_address(title: str, customer: str, line1: str, primary=False, shipping=
 			address_line1=line1,
 			city="Berlin",
 			country="Germany",
-			is_primary_address=int(primary),
-			is_shipping_address=int(shipping),
 			links=[{"link_doctype": "Customer", "link_name": customer}],
 		).insert()
 	return name

From a5e0f70da7b1df4736a67e1751e515f6b3318484 Mon Sep 17 00:00:00 2001
From: HenningWendtland <156231187+HenningWendtland@users.noreply.github.com>
Date: Tue, 8 Sep 2026 15:14:08 +0200
Subject: [PATCH 7/7] fix: remove commit from tests and add address template
 creation

---
 .../test_simple_subscription.py               | 59 +++++++++++--------
 1 file changed, 33 insertions(+), 26 deletions(-)

diff --git a/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py b/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py
index 2890c99..e9569ee 100644
--- a/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py
+++ b/simple_subscription/simple_subscription/doctype/simple_subscription/test_simple_subscription.py
@@ -7,10 +7,10 @@
 import frappe
 
 from .simple_subscription import (
+	CUSTOMER_LINK_FIELDS,
 	BillingTime,
 	Frequency,
 	PeriodType,
-	SimpleSubscription,
 	get_calendar_period,
 	get_date_period,
 	get_from_and_to_date,
@@ -202,37 +202,25 @@ def test_get_from_and_to_date(self):
 class TestSubscriptionCustomerData(unittest.TestCase):
 	"""Customer-bound Address/Contact links: the ownership check and the display properties.
 
-	Kept deliberately light. Anything that inserts a Simple Subscription needs a Company and an
-	Item, and anything that generates the invoice needs a fully set-up ERPNext site -- fixtures
-	that only the setup wizard creates and that CI (a bare `install-app erpnext`) does not have.
-	So these exercise the app's own logic on an in-memory document; that the invoice picks the
-	links up is ERPNext's `_get_party_details` doing its normal job.
+	Kept deliberately light. Generating the invoice needs a fully set-up ERPNext site -- Company,
+	Item Group, UOM, Price List, Fiscal Year -- fixtures that only the setup wizard creates and
+	that CI (a bare `install-app erpnext`) does not have. So these exercise the app's own logic on
+	an in-memory document, plus a meta check that the fieldnames create_invoice() forwards still
+	line up with the Sales Invoice.
 	"""
 
 	@classmethod
 	def setUpClass(cls):
 		super().setUpClass()
+		# never committed, so the fixtures die with the transaction -- same as IntegrationTestCase
+		cls.addClassCleanup(frappe.db.rollback)
+		make_default_address_template()
 		cls.customer = make_customer("_Test Sub Customer")
 		cls.other_customer = make_customer("_Test Sub Other Customer")
 		cls.address = make_address("_Test Sub Billing", cls.customer, "Rechnungsweg 1")
 		cls.other_address = make_address("_Test Sub Foreign", cls.other_customer, "Fremdweg 3")
 		cls.contact = make_contact("_Test Sub Contact", cls.customer)
 		cls.other_contact = make_contact("_Test Sub Foreign Contact", cls.other_customer)
-		frappe.db.commit()
-
-	@classmethod
-	def tearDownClass(cls):
-		for doctype, name in (
-			("Contact", cls.contact),
-			("Contact", cls.other_contact),
-			("Address", cls.address),
-			("Address", cls.other_address),
-			("Customer", cls.customer),
-			("Customer", cls.other_customer),
-		):
-			frappe.delete_doc(doctype, name, force=True, ignore_missing=True)
-		frappe.db.commit()
-		super().tearDownClass()
 
 	def make_subscription(self, **kwargs):
 		subscription = frappe.new_doc("Simple Subscription")
@@ -266,11 +254,11 @@ def test_rejects_links_of_another_customer(self):
 				)
 
 	def test_guards_the_links_after_submit_too(self):
-		"""The fields are allow_on_submit, and validate() does not run on update after submit."""
-		self.assertTrue(
-			hasattr(SimpleSubscription, "before_update_after_submit"),
-			"allow_on_submit links need a before_update_after_submit guard",
-		)
+		"""The fields are allow_on_submit, so validate() no longer runs once they change."""
+		meta = frappe.get_meta("Simple Subscription")
+		for fieldname in CUSTOMER_LINK_FIELDS:
+			self.assertTrue(meta.get_field(fieldname).allow_on_submit, fieldname)
+
 		subscription = self.make_subscription(customer_address=self.other_address)
 		self.assertRaisesRegex(
 			frappe.ValidationError,
@@ -296,6 +284,25 @@ def test_display_properties_are_empty_without_links(self):
 		self.assertIsNone(subscription.shipping_address_display)
 		self.assertIsNone(subscription.contact_display)
 
+	def test_link_fields_match_the_sales_invoice(self):
+		"""create_invoice() forwards these by name, so both doctypes have to spell them the same.
+
+		The forwarding itself needs a set-up site to exercise, so this is what guards it: a
+		renamed or retyped field on either side breaks the invoice silently, and fails here.
+		"""
+		subscription_meta = frappe.get_meta("Simple Subscription")
+		invoice_meta = frappe.get_meta("Sales Invoice")
+		for fieldname, doctype in CUSTOMER_LINK_FIELDS.items():
+			with self.subTest(fieldname=fieldname):
+				self.assertEqual(subscription_meta.get_field(fieldname).options, doctype)
+				self.assertEqual(invoice_meta.get_field(fieldname).options, doctype)
+
+
+def make_default_address_template() -> None:
+	"""Address.validate() renders the address, which needs one. A bare CI site has none."""
+	if not frappe.db.exists("Address Template", {"is_default": 1}):
+		frappe.get_doc(doctype="Address Template", country="Germany", is_default=1).insert()
+
 
 def make_customer(name: str) -> str:
 	if not frappe.db.exists("Customer", name):