add support for ?field__isnull=1 (#107)

* add support for ?field__isnull=1

* Add unit test and conditional formatting for ?field__isnull

datasette/utils.py

@@ -46,6 +46,7 @@ def build_where_clauses(args):
             'lte': '"{}" <= :{}',
             'glob': '"{}" glob :{}',
             'like': '"{}" like :{}',
+            'isnull': '"{}" is null',
         }[lookup]
         numeric_operators = {'gt', 'gte', 'lt', 'lte'}
         value_convert = {
@@ -56,11 +57,15 @@ def build_where_clauses(args):
         converted = value_convert(value)
         if lookup in numeric_operators and converted.isdigit():
             converted = int(converted)
-        param_id = 'p{}'.format(i)
+        if ':{}' in template:
+            param_id = 'p{}'.format(i)
+            params[param_id] = converted
+            tokens = (column, param_id)
+        else:
+            tokens = (column,)
         sql_bits.append(
-            template.format(column, param_id)
+            template.format(*tokens)
         )
-        params[param_id] = converted
     return sql_bits, params
 
 

tests/test_utils.py

@@ -88,6 +88,15 @@ def test_custom_json_encoder(obj, expected):
         ['"foo" like :p0', '"zax" glob :p1'],
         ['2%2', '3*']
     ),
+    (
+        {
+            'foo__isnull': '1',
+            'baz__isnull': '1',
+            'bar__gt': '10'
+        },
+        ['"bar" > :p0', '"baz" is null', '"foo" is null'],
+        [10]
+    ),
 ])
 def test_build_where(args, expected_where, expected_params):
     sql_bits, actual_params = utils.build_where_clauses(args)