Ensure parentheses used for CASE with subqueries.

Fixes #2873

peewee.py

@@ -1827,6 +1827,25 @@ def __sql__(self, ctx):
         return ctx.literal(self.window._alias or 'w')
 
 
+class Case(ColumnBase):
+    def __init__(self, predicate, expression_tuples, default=None):
+        self.predicate = predicate
+        self.expression_tuples = expression_tuples
+        self.default = default
+
+    def __sql__(self, ctx):
+        clauses = [SQL('CASE')]
+        if self.predicate is not None:
+            clauses.append(self.predicate)
+        for expr, value in self.expression_tuples:
+            clauses.extend((SQL('WHEN'), expr, SQL('THEN'), value))
+        if self.default is not None:
+            clauses.extend((SQL('ELSE'), self.default))
+        clauses.append(SQL('END'))
+        with ctx(in_function=False):
+            return ctx.sql(NodeList(clauses))
+
+
 class ForUpdate(Node):
     def __init__(self, expr, of=None, nowait=None):
         expr = 'FOR UPDATE' if expr is True else expr
@@ -1849,18 +1868,6 @@ def __sql__(self, ctx):
         return ctx
 
 
-def Case(predicate, expression_tuples, default=None):
-    clauses = [SQL('CASE')]
-    if predicate is not None:
-        clauses.append(predicate)
-    for expr, value in expression_tuples:
-        clauses.extend((SQL('WHEN'), expr, SQL('THEN'), value))
-    if default is not None:
-        clauses.extend((SQL('ELSE'), default))
-    clauses.append(SQL('END'))
-    return NodeList(clauses)
-
-
 class NodeList(ColumnBase):
     def __init__(self, nodes, glue=' ', parens=False):
         self.nodes = nodes

tests/regressions.py

@@ -1811,3 +1811,15 @@ def test_iteration_single_query(self):
             list(User.select())
         with self.assertQueryCount(1):
             self.assertEqual(User.select().count(), 0)
+
+
+class TestSumCaseSubquery(ModelTestCase):
+    requires = [Sample]
+
+    def test_sum_case_subquery(self):
+        Sample.insert_many([(i, i) for i in range(5)]).execute()
+
+        subq = Sample.select().where(Sample.counter.in_([1, 3, 5]))
+        case = Case(None, [(Sample.id.in_(subq), Sample.value)], 0)
+        q = Sample.select(fn.SUM(case))
+        self.assertEqual(q.scalar(), 4.0)

tests/sql.py

@@ -1793,6 +1793,16 @@ def test_case_function(self):
             'ELSE ? END '
             'FROM "nn" AS "t1"'), [1, 'one', 2, 'two', '?'])
 
+    def test_case_subquery(self):
+        Name = Table('n', ('id', 'name',))
+        case = Case(None, [(Name.id.in_(Name.select(Name.id)), 1)], 0)
+        q = Name.select(fn.SUM(case))
+        self.assertSQL(q, (
+            'SELECT SUM('
+            'CASE WHEN ("t1"."id" IN (SELECT "t1"."id" FROM "n" AS "t1")) '
+            'THEN ? ELSE ? END) FROM "n" AS "t1"'), [1, 0])
+
+
 
 class TestSelectFeatures(BaseTestCase):
     def test_reselect(self):