From b1c359a562ec19f0007e64866f3e3b1afeeaf222 Mon Sep 17 00:00:00 2001
From: Ryan P Kilby <rpkilby@ncsu.edu>
Date: Mon, 15 Jan 2018 02:42:48 -0500
Subject: [PATCH] Make lookup required when value is provided

---
 django_filters/fields.py | 13 +++++++++++--
 tests/test_fields.py     |  3 +++
 tests/test_filtering.py  |  9 +++++++++
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/django_filters/fields.py b/django_filters/fields.py
index b1126015a..b6903ba16 100644
--- a/django_filters/fields.py
+++ b/django_filters/fields.py
@@ -92,6 +92,10 @@ def __new__(cls, value, lookup_expr):
 
 
 class LookupChoiceField(forms.MultiValueField):
+    default_error_messages = {
+        'lookup_required': _('Select a lookup.'),
+    }
+
     def __init__(self, field, lookup_choices, *args, **kwargs):
         empty_label = kwargs.pop('empty_label', settings.EMPTY_CHOICE_LABEL)
         fields = (field, ChoiceField(choices=lookup_choices, empty_label=empty_label))
@@ -103,8 +107,13 @@ def __init__(self, field, lookup_choices, *args, **kwargs):
     def compress(self, data_list):
         if len(data_list) == 2:
             value, lookup_expr = data_list
-            if value not in EMPTY_VALUES and lookup_expr not in EMPTY_VALUES:
-                return Lookup(value=value, lookup_expr=lookup_expr)
+            if value not in EMPTY_VALUES:
+                if lookup_expr not in EMPTY_VALUES:
+                    return Lookup(value=value, lookup_expr=lookup_expr)
+                else:
+                    raise forms.ValidationError(
+                        self.error_messages['lookup_required'],
+                        code='lookup_required')
         return None
 
 
diff --git a/tests/test_fields.py b/tests/test_fields.py
index 98aeaf9f4..5b251227a 100644
--- a/tests/test_fields.py
+++ b/tests/test_fields.py
@@ -122,6 +122,9 @@ def test_clean(self):
             f.clean([]),
             None)
 
+        with self.assertRaisesMessage(forms.ValidationError, 'Select a lookup.'):
+            f.clean(['12.34', ''])
+
     def test_render_used_html5(self):
         inner = forms.DecimalField()
         f = LookupChoiceField(inner, [('gt', 'gt'), ('lt', 'lt')], empty_label=None)
diff --git a/tests/test_filtering.py b/tests/test_filtering.py
index fa8c760ca..6571c8fdc 100644
--- a/tests/test_filtering.py
+++ b/tests/test_filtering.py
@@ -1644,10 +1644,12 @@ def test_filtering(self):
         f = F({'price': '15', 'price_lookup': 'lt'})
         self.assertQuerysetEqual(f.qs, ['Ender\'s Game'], lambda o: o.title)
         f = F({'price': '', 'price_lookup': 'lt'})
+        self.assertTrue(f.is_valid())
         self.assertQuerysetEqual(f.qs,
                                  ['Ender\'s Game', 'Rainbow Six', 'Snowcrash'],
                                  lambda o: o.title, ordered=False)
         f = F({'price': '15'})
+        self.assertFalse(f.is_valid())
         self.assertQuerysetEqual(f.qs,
                                  ['Ender\'s Game', 'Rainbow Six', 'Snowcrash'],
                                  lambda o: o.title, ordered=False)
@@ -1666,6 +1668,13 @@ def test_lookup_choices_validation(self):
             'price': ['Select a valid choice. asdf is not one of the available choices.'],
         })
 
+    def test_lookup_omitted(self):
+        f = self.BookFilter({'price': '1'})
+        self.assertFalse(f.is_valid())
+        self.assertEqual(f.errors, {
+            'price': ['Select a lookup.'],
+        })
+
 
 # use naive datetimes, as pytz is required to perform
 # date lookups when timezones are involved.