From 401cba23b7aaa6ea8ed1d9be5152027b6dbbda96 Mon Sep 17 00:00:00 2001
From: Lance Edgar <lance@edbob.org>
Date: Sun, 22 Oct 2017 20:00:31 -0700
Subject: [PATCH] Add grid filter which treats empty string as NULL

---
 tailbone/grids/core.py    |  3 +++
 tailbone/grids/filters.py | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/tailbone/grids/core.py b/tailbone/grids/core.py
index 4f79587b..7729a536 100644
--- a/tailbone/grids/core.py
+++ b/tailbone/grids/core.py
@@ -123,6 +123,9 @@ class Grid(object):
     def set_sorter(self, key, *args, **kwargs):
         self.sorters[key] = self.make_sorter(*args, **kwargs)
 
+    def set_filter(self, key, *args, **kwargs):
+        self.filters[key] = self.make_filter(key, *args, **kwargs)
+
     def set_label(self, key, label):
         self.labels[key] = label
         if key in self.filters:
diff --git a/tailbone/grids/filters.py b/tailbone/grids/filters.py
index 87964693..e5618320 100644
--- a/tailbone/grids/filters.py
+++ b/tailbone/grids/filters.py
@@ -334,6 +334,24 @@ class AlchemyStringFilter(AlchemyGridFilter):
         ))
 
 
+class AlchemyEmptyStringFilter(AlchemyStringFilter):
+    """
+    String filter with special logic to treat empty string values as NULL
+    """
+
+    def filter_is_null(self, query, value):
+        return query.filter(
+            sa.or_(
+                self.column == None,
+                sa.func.trim(self.column) == ''))
+
+    def filter_is_not_null(self, query, value):
+        return query.filter(
+            sa.and_(
+                self.column != None,
+                sa.func.trim(self.column) != ''))
+
+
 class AlchemyByteStringFilter(AlchemyStringFilter):
     """
     String filter for SQLAlchemy, which encodes value as bytestring before