From 3ec4e739dd4ac3f1dea92cdec858bf491f63d5e8 Mon Sep 17 00:00:00 2001
From: Attila Tovt <uran198@gmail.com>
Date: Sun, 22 Nov 2015 02:59:37 +0200
Subject: [1.8.x] Fixed #25772 -- Corrected __len lookup on ArrayField for
 empty arrays.

Backport of 88fc9e2826044110b7b22577a227f122fe9c1fb5 from master
---
 django/contrib/postgres/fields/array.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

(limited to 'django/contrib/postgres/fields/array.py')

diff --git a/django/contrib/postgres/fields/array.py b/django/contrib/postgres/fields/array.py
index 87760613fb..ceac798604 100644
--- a/django/contrib/postgres/fields/array.py
+++ b/django/contrib/postgres/fields/array.py
@@ -198,7 +198,11 @@ class ArrayLenTransform(Transform):
 
     def as_sql(self, compiler, connection):
         lhs, params = compiler.compile(self.lhs)
-        return 'array_length(%s, 1)' % lhs, params
+        # Distinguish NULL and empty arrays
+        return (
+            'CASE WHEN %(lhs)s IS NULL THEN NULL ELSE '
+            'coalesce(array_length(%(lhs)s, 1), 0) END'
+        ) % {'lhs': lhs}, params
 
 
 class IndexTransform(Transform):
-- 
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