From f2ad4cea3c8a6fb3f06aa8c8326a6b1e18f26477 Mon Sep 17 00:00:00 2001
From: Karl Hobley <karl@kaed.uk>
Date: Fri, 20 Oct 2017 10:40:00 +0100
Subject: [PATCH] Fix __isnull=True lookup for Elasticsearch 5

---
 wagtail/search/backends/elasticsearch5.py     | 21 +++++++++++++++++++
 .../tests/test_elasticsearch5_backend.py      |  9 ++------
 2 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/wagtail/search/backends/elasticsearch5.py b/wagtail/search/backends/elasticsearch5.py
index d8bf370b7..0c43b16b3 100644
--- a/wagtail/search/backends/elasticsearch5.py
+++ b/wagtail/search/backends/elasticsearch5.py
@@ -16,6 +16,27 @@ class Elasticsearch5Index(Elasticsearch2Index):
 class Elasticsearch5SearchQuery(Elasticsearch2SearchQuery):
     mapping_class = Elasticsearch5Mapping
 
+    def _process_lookup(self, field, lookup, value):
+        column_name = self.mapping.get_field_column_name(field)
+
+        if lookup == 'isnull':
+            query = {
+                'exists': {
+                    'field': column_name,
+                }
+            }
+
+            if value:
+                query = {
+                    'bool': {
+                        'mustNot': query
+                    }
+                }
+
+            return query
+
+        return super(Elasticsearch5SearchQuery, self)._process_lookup(field, lookup, value)
+
     def _connect_filters(self, filters, connector, negated):
         if filters:
             if len(filters) == 1:
diff --git a/wagtail/search/tests/test_elasticsearch5_backend.py b/wagtail/search/tests/test_elasticsearch5_backend.py
index 228cd85a3..205f50d13 100644
--- a/wagtail/search/tests/test_elasticsearch5_backend.py
+++ b/wagtail/search/tests/test_elasticsearch5_backend.py
@@ -18,11 +18,6 @@ from .test_backends import BackendTests
 class TestElasticsearch5SearchBackend(BackendTests, ElasticsearchCommonSearchBackendTests, TestCase):
     backend_path = 'wagtail.search.backends.elasticsearch5'
 
-    # Broken
-    @unittest.expectedFailure
-    def test_filter_isnull_true(self):
-        super(TestElasticsearch5SearchBackend, self).test_filter_isnull_true()
-
     # Broken
     @unittest.expectedFailure
     def test_delete(self):
@@ -190,7 +185,7 @@ class TestElasticsearch5SearchQuery(TestCase):
         # Check it
         expected_result = {'bool': {'filter': [
             {'match': {'content_type': 'searchtests.Book'}},
-            {'missing': {'field': 'title_filter'}}
+            {'bool': {'mustNot': {'exists': {'field': 'title_filter'}}}}
         ], 'must': {'multi_match': {'query': 'Hello', 'fields': ['_all', '_partials']}}}}
         self.assertDictEqual(query.get_query(), expected_result)
 
@@ -201,7 +196,7 @@ class TestElasticsearch5SearchQuery(TestCase):
         # Check it
         expected_result = {'bool': {'filter': [
             {'match': {'content_type': 'searchtests.Book'}},
-            {'missing': {'field': 'title_filter'}}
+            {'bool': {'mustNot': {'exists': {'field': 'title_filter'}}}}
         ], 'must': {'multi_match': {'query': 'Hello', 'fields': ['_all', '_partials']}}}}
         self.assertDictEqual(query.get_query(), expected_result)