Add example custom type

README.md

@@ -145,7 +145,7 @@ added for additional types like point, hstore, numeric, etc. that do not have
 direct mappings in Go by the types implementing Scanner, TextEncoder, and
 optionally BinaryEncoder. To enable binary format for custom types, a prepared
 statement must be used and the field description of the returned field must have
-FormatCode set to BinaryFormatCode. See example_value_transcoder_test.go for an
+FormatCode set to BinaryFormatCode. See example_custom_type_test.go for an
 example of a custom type for the PostgreSQL point type.
 
 ### Null Mapping

example_custom_type_test.go

@@ -0,0 +1,99 @@
+package pgx_test
+
+import (
+	"errors"
+	"fmt"
+	"github.com/jackc/pgx"
+	"regexp"
+	"strconv"
+)
+
+var pointRegexp *regexp.Regexp = regexp.MustCompile(`^\((.*),(.*)\)$`)
+
+// NullPoint represents a point that may be null.
+//
+// If Valid is false then the value is NULL.
+type NullPoint struct {
+	X, Y  float64 // Coordinates of point
+	Valid bool    // Valid is true if not NULL
+}
+
+const pointOid = 600
+
+func (p *NullPoint) Scan(vr *pgx.ValueReader) error {
+	if vr.Type().DataType != pointOid {
+		return pgx.SerializationError(fmt.Sprintf("NullPoint.Scan cannot decode OID %d", vr.Type().DataType))
+	}
+
+	if vr.Len() == -1 {
+		p.X, p.Y, p.Valid = 0, 0, false
+		return nil
+	}
+
+	switch vr.Type().FormatCode {
+	case pgx.TextFormatCode:
+		s := vr.ReadString(vr.Len())
+		match := pointRegexp.FindStringSubmatch(s)
+		if match == nil {
+			return pgx.SerializationError(fmt.Sprintf("Received invalid point: %v", s))
+		}
+
+		var err error
+		p.X, err = strconv.ParseFloat(match[1], 64)
+		if err != nil {
+			return pgx.SerializationError(fmt.Sprintf("Received invalid point: %v", s))
+		}
+		p.Y, err = strconv.ParseFloat(match[2], 64)
+		if err != nil {
+			return pgx.SerializationError(fmt.Sprintf("Received invalid point: %v", s))
+		}
+	case pgx.BinaryFormatCode:
+		return errors.New("binary format not implemented")
+	default:
+		return fmt.Errorf("unknown format %v", vr.Type().FormatCode)
+	}
+
+	p.Valid = true
+	return vr.Err()
+}
+
+func (p NullPoint) EncodeText() (string, byte, error) {
+	if p.Valid {
+		return fmt.Sprintf("point(%v,%v)", p.X, p.Y), pgx.SafeText, nil
+	} else {
+		return "", pgx.NullText, nil
+	}
+}
+
+func (p NullPoint) String() string {
+	if p.Valid {
+		return fmt.Sprintf("%v, %v", p.X, p.Y)
+	}
+	return "null point"
+}
+
+func Example_CustomType() {
+	conn, err := pgx.Connect(*defaultConnConfig)
+	if err != nil {
+		fmt.Printf("Unable to establish connection: %v", err)
+		return
+	}
+
+	var p NullPoint
+	err = conn.QueryRow("select null::point").Scan(&p)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	fmt.Println(p)
+
+	err = conn.QueryRow("select point(1.5,2.5)").Scan(&p)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	fmt.Println(p)
+	// Output:
+	// null point
+	// 1.5, 2.5
+}