example_udt_unmarshaler_test.go

package gocql_test

import (
	"context"
	"fmt"
	"github.com/gocql/gocql"
	"log"
)

// MyUDTUnmarshaler implements UDTUnmarshaler.
type MyUDTUnmarshaler struct {
	fieldA string
	fieldB int32
}

// UnmarshalUDT unmarshals the field identified by name into MyUDTUnmarshaler.
func (m *MyUDTUnmarshaler) UnmarshalUDT(name string, info gocql.TypeInfo, data []byte) error {
	switch name {
	case "field_a":
		return gocql.Unmarshal(info, data, &m.fieldA)
	case "field_b":
		return gocql.Unmarshal(info, data, &m.fieldB)
	default:
		// If you want to be strict and return error un unknown field, you can do so here instead.
		// Returning nil will ignore unknown fields, which might be handy if you want
		// to be forward-compatible when a new field is added to the UDT.
		return nil
	}
}

// ExampleUDTUnmarshaler demonstrates how to implement a UDTUnmarshaler.
func ExampleUDTUnmarshaler() {
	/* The example assumes the following CQL was used to setup the keyspace:
	create keyspace example with replication = { 'class' : 'SimpleStrategy', 'replication_factor' : 1 };
	create type example.my_udt (field_a text, field_b int);
	create table example.my_udt_table(pk int, value frozen<my_udt>, PRIMARY KEY(pk));
	insert into example.my_udt_table (pk, value) values (1, {field_a: 'a value', field_b: 42});
	*/
	cluster := gocql.NewCluster("localhost:9042")
	cluster.Keyspace = "example"
	cluster.ProtoVersion = 4
	session, err := cluster.CreateSession()
	if err != nil {
		log.Fatal(err)
	}
	defer session.Close()

	ctx := context.Background()

	var value MyUDTUnmarshaler
	err = session.Query("SELECT value FROM example.my_udt_table WHERE pk = 1").WithContext(ctx).Scan(&value)
	if err != nil {
		log.Fatal(err)
	}
	fmt.Println(value.fieldA)
	fmt.Println(value.fieldB)
	// a value
	// 42
}