vendors: restrict deletion

* Prevents the deletion of a vendor record when a holdings is attached
  to it.
* Closes rero#1822.

Co-Authored-by: Renaud Michotte <renaud.michotte@gmail.com>

rero_ils/modules/vendors/api.py

@@ -77,26 +77,21 @@ def order_email(self):
             'order_contact', self.get('default_contact', {})
         ).get('email')
 
-    def get_number_of_acq_orders(self):
+    def count_links_to_me(self, search_class):
         """Get number of acquisition orders."""
-        return AcqOrdersSearch().filter(
-            'term', vendor__pid=self.pid).source().count()
-
-    def get_number_of_acq_invoices(self):
-        """Get number of acquisition invoices."""
-        return AcquisitionInvoicesSearch().filter(
-            'term', vendor__pid=self.pid).source().count()
+        return search_class()\
+            .filter('term', vendor__pid=self.pid)\
+            .source().count()
 
     def get_links_to_me(self):
         """Get number of links."""
-        links = {}
-        acq_orders = self.get_number_of_acq_orders()
-        if acq_orders:
-            links['acq_orders'] = acq_orders
-
-        acq_invoices = self.get_number_of_acq_invoices()
-        if acq_invoices:
-            links['acq_invoices'] = acq_invoices
+        from rero_ils.modules.holdings.api import HoldingsSearch
+        links = {
+            'acq_orders': self.count_links_to_me(AcqOrdersSearch),
+            'acq_invoices': self.count_links_to_me(AcquisitionInvoicesSearch),
+            'holdings': self.count_links_to_me(HoldingsSearch),
+        }
+        links = {k: v for k, v in links.items() if v}
         return links
 
     def reasons_not_to_delete(self):

tests/api/vendors/test_vendors.py

@@ -73,13 +73,14 @@ def test_filtered_vendors_get(client, librarian_martigny,
 
 def test_vendors_can_delete(
         client, vendor_martigny, acq_order_fiction_martigny,
-        acq_invoice_fiction_martigny):
+        acq_invoice_fiction_martigny, holding_lib_martigny_w_patterns):
     """Test can delete a vendor with a linked acquisition order."""
     assert not vendor_martigny.can_delete
 
     reasons = vendor_martigny.reasons_not_to_delete()
     assert reasons['links']['acq_orders']
     assert reasons['links']['acq_invoices']
+    assert reasons['links']['holdings']
 
 
 def test_vendor_post_update_delete(client, librarian_martigny,