🐛 Fix mods:relatedItem with mods:recordIdentifier source=dnb-ppn

mods:relatedItem may have a mods:recordIdentifier with source="dnb-ppn".
This may happen for digitized works that have their original work in
another library and use a DNB PPN there.

Fixes gh-22.

qurator/mods4pandas/mods4pandas.py

@@ -95,7 +95,13 @@ def mods_to_dict(mods, raise_errors=True):
         elif tag == '{http://www.loc.gov/mods/v3}recordInfo':
             value['recordInfo'] = TagGroup(tag, group).is_singleton().has_no_attributes().descend(raise_errors)
         elif tag == '{http://www.loc.gov/mods/v3}recordIdentifier':
-            value['recordIdentifier'] = TagGroup(tag, group).is_singleton().has_attributes({'source': 'gbv-ppn'}).text()
+            # By default we assume source="gbv-ppn" mods:recordIdentifiers (= PPNs),
+            # however, in mods:relatedItems, there may be source="dnb-ppns",
+            # which we need to distinguish by using a separate field name.
+            try:
+                value['recordIdentifier'] = TagGroup(tag, group).is_singleton().has_attributes({'source': 'gbv-ppn'}).text()
+            except ValueError:
+                value['recordIdentifier-dnb-ppn'] = TagGroup(tag, group).is_singleton().has_attributes({'source': 'dnb-ppn'}).text()
         elif tag == '{http://www.loc.gov/mods/v3}identifier':
             for e in group:
                 if len(e.attrib) != 1:

qurator/mods4pandas/tests/test_modstool.py

@@ -138,3 +138,16 @@ def test_relatedItem():
     """)
 
     assert d['relatedItem-original_recordInfo_recordIdentifier'] == 'PPN167755803'
+
+    # mods:relatedItem may also have source="dnb-ppn" recordIdentifiers:
+    d = dict_fromstring("""
+    <mods:mods xmlns:mods="http://www.loc.gov/mods/v3">
+        <mods:relatedItem type="original">
+            <mods:recordInfo>
+                <mods:recordIdentifier source="dnb-ppn">1236513355</mods:recordIdentifier>
+            </mods:recordInfo>
+        </mods:relatedItem>
+    </mods:mods>
+    """)
+
+    assert d['relatedItem-original_recordInfo_recordIdentifier-dnb-ppn'] == '1236513355'