Add support for CASE operator.

sqlbuilder/func_expression.go

@@ -1,5 +1,7 @@
 package sqlbuilder
 
+import "errors"
+
 type funcExpressionImpl struct {
 	expressionInterfaceImpl
 
@@ -63,3 +65,98 @@ func MAX(expression NumericExpression) NumericExpression {
 func SUM(expression NumericExpression) NumericExpression {
 	return NewNumericFunc("SUM", expression)
 }
+
+type caseInterface interface {
+	Expression
+
+	WHEN(condition Expression) caseInterface
+	THEN(then Expression) caseInterface
+	ELSE(els Expression) caseInterface
+}
+
+type caseExpression struct {
+	expressionInterfaceImpl
+
+	expression Expression
+	when       []Expression
+	then       []Expression
+	els        Expression
+}
+
+func CASE(expression ...Expression) caseInterface {
+	caseExp := &caseExpression{}
+
+	if len(expression) == 1 {
+		caseExp.expression = expression[0]
+	}
+
+	caseExp.expressionInterfaceImpl.parent = caseExp
+
+	return caseExp
+}
+
+func (c *caseExpression) WHEN(when Expression) caseInterface {
+	c.when = append(c.when, when)
+	return c
+}
+
+func (c *caseExpression) THEN(then Expression) caseInterface {
+	c.then = append(c.then, then)
+	return c
+}
+
+func (c *caseExpression) ELSE(els Expression) caseInterface {
+	c.els = els
+
+	return c
+}
+
+func (c *caseExpression) Serialize(out *queryData, options ...serializeOption) error {
+	out.WriteString("(CASE")
+
+	if c.expression != nil {
+		out.WriteString(" ")
+		err := c.expression.Serialize(out)
+
+		if err != nil {
+			return err
+		}
+	}
+
+	if len(c.when) == 0 || len(c.then) == 0 {
+		return errors.New("Invalid case statement. There should be at least one when/then expression pair. ")
+	}
+
+	if len(c.when) != len(c.then) {
+		return errors.New("When and then expression count mismatch. ")
+	}
+
+	for i, when := range c.when {
+		out.WriteString(" WHEN ")
+		err := when.Serialize(out)
+
+		if err != nil {
+			return err
+		}
+
+		out.WriteString(" THEN ")
+		err = c.then[i].Serialize(out)
+
+		if err != nil {
+			return err
+		}
+	}
+
+	if c.els != nil {
+		out.WriteString(" ELSE ")
+		err := c.els.Serialize(out)
+
+		if err != nil {
+			return err
+		}
+	}
+
+	out.WriteString(" END)")
+
+	return nil
+}