dialect/sql: fix predicate builder on join

Summary: Pull Request resolved: https://github.com/facebookincubator/ent/pull/143

Reviewed By: idoshveki

Differential Revision: D18346652

fbshipit-source-id: e8c5d7eb3cefc16f52090de0d121e82cae058fc2

dialect/sql/builder.go

@@ -731,6 +731,9 @@ func P() *Predicate { return &Predicate{} }
 //
 func Or(preds ...*Predicate) *Predicate {
 	return P().append(func(b *Builder) {
+		if len(preds) > 1 {
+			b.WriteString("(")
+		}
 		for i := range preds {
 			if i > 0 {
 				b.WriteString(" OR ")
@@ -739,6 +742,9 @@ func Or(preds ...*Predicate) *Predicate {
 				b.Join(preds[i])
 			})
 		}
+		if len(preds) > 1 {
+			b.WriteString(")")
+		}
 	})
 }
 
@@ -1317,6 +1323,19 @@ func (s *Selector) Where(p *Predicate) *Selector {
 	return s
 }
 
+// P returns the predicate of a selector.
+func (s *Selector) P() *Predicate {
+	return s.where
+}
+
+// SetP sets explicitly the predicate function for the selector and clear its previous state.
+func (s *Selector) SetP(p *Predicate) *Selector {
+	s.where = p
+	s.or = false
+	s.not = false
+	return s
+}
+
 // FromSelect copies the predicate from a selector.
 func (s *Selector) FromSelect(s2 *Selector) *Selector {
 	s.where = s2.where