Allow setting parent id in doc metadata

This makes the API more consistent between physical and logical domains.

pagexml/model/physical_document_model.py

@@ -483,6 +483,13 @@ def set_derived_id(self, parent_id: str):
         self.id = f"{parent_id}-{self.main_type}-{box_string}"
         # self.metadata['id'] = self.id
 
+    def add_parent_id_to_metadata(self):
+        if self.parent:
+            self.metadata['parent_type'] = self.parent.main_type
+            self.metadata['parent_id'] = self.parent.id
+            if hasattr(self.parent, 'main_type') and self.parent.main_type is not None:
+                self.metadata[f'{self.parent.main_type}_id'] = self.parent.id
+
 
 class LogicalStructureDoc(StructureDoc):
 

tests/physical_document_model_test.py

@@ -176,6 +176,14 @@ def test_set_derived_id(self):
         self.doc.set_derived_id(parent.id)
         self.assertEqual('parent_doc-book-0-0-10-10', self.doc.id)
 
+    def test_add_parent_id_to_metadata(self):
+        child = pdm.PhysicalStructureDoc(doc_id='doc2', doc_type='chapter')
+        child.id = 'parent_doc'
+        self.doc.set_as_parent([child])
+        self.doc.add_parent_id_to_metadata()
+        self.assertIn('book_id', child.metadata)
+        self.assertEqual('doc1', child.metadata['book_id'])
+
     def test_json(self):
         expected_json = {
             'id': 'doc1',