Implement bulk_to_python on ListBlock

wagtail/core/blocks/list_block.py

@@ -1,3 +1,5 @@
+import itertools
+
 from django import forms
 from django.core.exceptions import ValidationError
 from django.forms.utils import ErrorList
@@ -137,6 +139,22 @@ class ListBlock(Block):
         # 'value' is a list of child block values; use bulk_to_python to convert them all in one go
         return self.child_block.bulk_to_python(value)
 
+    def bulk_to_python(self, values):
+        # 'values' is a list of lists of child block values; concatenate them into one list so that
+        # we can make a single call to child_block.bulk_to_python
+        lengths = [len(val) for val in values]
+        raw_values = list(itertools.chain.from_iterable(values))
+        converted_values = self.child_block.bulk_to_python(raw_values)
+
+        # split converted_values back into sub-lists of the original lengths
+        result = []
+        offset = 0
+        for sublist_len in lengths:
+            result.append(converted_values[offset:offset + sublist_len])
+            offset += sublist_len
+
+        return result
+
     def get_prep_value(self, value):
         # recursively call get_prep_value on children and return as a list
         return [

wagtail/core/tests/test_blocks.py

@@ -2342,6 +2342,18 @@ class TestListBlockWithFixtures(TestCase):
 
         self.assertSequenceEqual(pages, expected_pages)
 
+    def test_bulk_to_python(self):
+        block = blocks.ListBlock(blocks.PageChooserBlock())
+
+        with self.assertNumQueries(1):
+            result = block.bulk_to_python([[4, 5], [], [2]])
+
+        self.assertEqual(result, [
+            [Page.objects.get(id=4), Page.objects.get(id=5)],
+            [],
+            [Page.objects.get(id=2)],
+        ])
+
 
 class TestStreamBlock(WagtailTestUtils, SimpleTestCase):
     def test_initialisation(self):