Add custom value transcoder example

example_value_transcoder_test.go

@@ -0,0 +1,59 @@
+package pgx_test
+
+import (
+	"fmt"
+	"github.com/JackC/pgx"
+	"regexp"
+	"strconv"
+)
+
+var pointRegexp *regexp.Regexp = regexp.MustCompile(`^\((.*),(.*)\)$`)
+
+type Point struct {
+	x float64
+	y float64
+}
+
+func (p Point) String() string {
+	return fmt.Sprintf("%v, %v", p.x, p.y)
+}
+
+func Example_customValueTranscoder() {
+	pgx.ValueTranscoders[pgx.Oid(600)] = &pgx.ValueTranscoder{
+		DecodeText: decodePointFromText,
+		EncodeTo:   encodePoint}
+
+	conn := getSharedConnection()
+
+	v, _ := conn.SelectValue("select point(1.5,2.5)")
+	fmt.Println(v)
+	// Output:
+	// 1.5, 2.5
+}
+
+func decodePointFromText(mr *pgx.MessageReader, size int32) interface{} {
+	s := mr.ReadByteString(size)
+	match := pointRegexp.FindStringSubmatch(s)
+	if match == nil {
+		panic(fmt.Sprintf("Received invalid point: %v", s))
+	}
+
+	var err error
+	var p Point
+	p.x, err = strconv.ParseFloat(match[1], 64)
+	if err != nil {
+		panic(fmt.Sprintf("Received invalid point: %v", s))
+	}
+	p.y, err = strconv.ParseFloat(match[2], 64)
+	if err != nil {
+		panic(fmt.Sprintf("Received invalid point: %v", s))
+	}
+	return p
+}
+
+func encodePoint(w *pgx.MessageWriter, value interface{}) {
+	p := value.(Point)
+	s := fmt.Sprintf("point(%v,%v)", p.x, p.y)
+	w.Write(int32(len(s)))
+	w.WriteString(s)
+}