feat(#282): allow ordering by case expression

Author: doug-martin

exp/case.go

@@ -73,3 +73,6 @@ func (c caseExpression) Else(result interface{}) CaseExpression {
 	c.elseCondition = NewCaseElse(result)
 	return c
 }
+
+func (c caseExpression) Asc() OrderedExpression  { return asc(c) }
+func (c caseExpression) Desc() OrderedExpression { return desc(c) }

exp/case_test.go

@@ -57,6 +57,16 @@ func (ces *caseExpressionSuite) TestElse() {
 	ces.Nil(ce.GetElse())
 }
 
+func (ces *caseExpressionSuite) TestAsc() {
+	ce := exp.NewCaseExpression()
+	ces.Equal(exp.NewOrderedExpression(ce, exp.AscDir, exp.NoNullsSortType), ce.Asc())
+}
+
+func (ces *caseExpressionSuite) TestDesc() {
+	ce := exp.NewCaseExpression()
+	ces.Equal(exp.NewOrderedExpression(ce, exp.DescSortDir, exp.NoNullsSortType), ce.Desc())
+}
+
 type caseWhenSuite struct {
 	suite.Suite
 }

exp/exp.go

@@ -455,6 +455,7 @@ type (
 	CaseExpression interface {
 		Expression
 		Aliaseable
+		Orderable
 		GetValue() interface{}
 		GetWhens() []CaseWhen
 		GetElse() CaseElse

select_dataset_example_test.go

@@ -380,6 +380,14 @@ func ExampleSelectDataset_Order() {
 	// SELECT * FROM "test" ORDER BY "a" ASC
 }
 
+func ExampleSelectDataset_Order_caseExpression() {
+	ds := goqu.From("test").Order(goqu.Case().When(goqu.C("num").Gt(10), 0).Else(1).Asc())
+	sql, _, _ := ds.ToSQL()
+	fmt.Println(sql)
+	// Output:
+	// SELECT * FROM "test" ORDER BY CASE  WHEN ("num" > 10) THEN 0 ELSE 1 END ASC
+}
+
 func ExampleSelectDataset_OrderAppend() {
 	ds := goqu.From("test").Order(goqu.C("a").Asc())
 	sql, _, _ := ds.OrderAppend(goqu.C("b").Desc().NullsLast()).ToSQL()