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当然,想必您已经猜到了,在对一些复杂类型(如struct
)的转换时,gconv
模块内部其实使用了反射的特性来实现的。这虽然为开发者提供了极大的便捷,但是这确实是以性能损耗为代价的。其实在对于struct
转换时,如果开发者已经明确转换规则,并且对于其中的性能损耗比较在意,那么可以对特定的struct
实现UnmarshalValue
接口来实现自定义转换。当使用gconv
模块对该struct
进行转换时,无论该struct
是直接作为转换对象或者转换对象的属性,gconv
都将会自动识别其实现的UnmarshalValue
接口并直接调用该接口实现类型转换,而不会使用反射特性来实现转换。
Tip |
---|
标准库的常用反序列化接口,如 |
接口定义
// apiUnmarshalValue is the interface for custom defined types customizing value assignment.
// Note that only pointer can implement interface apiUnmarshalValue.
type apiUnmarshalValue interface {
UnmarshalValue(interface{}) error
}
可以看到,自定义的类型可以通过定义UnmarshalValue
方法来实现自定义的类型转换。这里的输入参数为interface{}
类型,开发者可以在实际使用场景中通过 类型断言 或者其他方式进行类型转换。
Warning | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|
需要特别注意,由于 正确的接口实现定义示例(使用指针接受):
错误的接口实现定义示例(使用了值传递):
|
使用示例
1、自定义数据表查询结果struct
转换
数据表结构:
Code Block | ||
---|---|---|
| ||
CREATE TABLE `user` (
id bigint unsigned NOT NULL AUTO_INCREMENT,
passport varchar(45),
password char(32) NOT NULL,
nickname varchar(45) NOT NULL,
create_time timestamp NOT NULL,
PRIMARY KEY (id)
) ; |
示例代码:
Code Block | ||
---|---|---|
| ||
package main
import (
"fmt"
"github.com/gogf/gf/container/garray"
"github.com/gogf/gf/database/gdb"
"github.com/gogf/gf/frame/g"
"github.com/gogf/gf/os/gtime"
"github.com/gogf/gf/util/gconv"
)
type User struct {
Id int
Passport string
Password string
Nickname string
CreateTime *gtime.Time
}
func (user *User) UnmarshalValue(value interface{}) error {
switch result := value.(type) {
case map[string]interface{}:
user.Id = result["id"].(gdb.Value).Int()
user.Passport = result["passport"].(gdb.Value).String()
user.Password = ""
user.Nickname = result["nickname"].(gdb.Value).String()
user.CreateTime = result["create_time"].(gdb.Value).GTime()
return nil
default:
return gconv.Struct(value, user)
}
}
func main() {
var (
err error
users []*User
)
array := garray.New(true)
for i := 1; i <= 10; i++ {
array.Append(g.Map{
"id": i,
"passport": fmt.Sprintf(`user_%d`, i),
"password": fmt.Sprintf(`pass_%d`, i),
"nickname": fmt.Sprintf(`name_%d`, i),
"create_time": gtime.NewFromStr("2018-10-24 10:00:00").String(),
})
}
// 写入数据
_, err = g.DB().BatchInsert("user", array.Slice())
if err != nil {
panic(err)
}
// 查询数据
err = g.Model("user").Order("id asc").Scan(&users)
if err != nil {
panic(err)
}
g.Dump(users)
} |
执行后,终端输出:
Code Block | ||
---|---|---|
| ||
[
{
"Id": 1,
"Passport": "user_1",
"Password": "",
"Nickname": "name_1",
"CreateTime": "2018-10-24 10:00:00"
},
{
"Id": 2,
"Passport": "user_2",
"Password": "",
"Nickname": "name_2",
"CreateTime": "2018-10-24 10:00:00"
},
{
"Id": 3,
"Passport": "user_3",
"Password": "",
"Nickname": "name_3",
"CreateTime": "2018-10-24 10:00:00"
},
{
"Id": 4,
"Passport": "user_4",
"Password": "",
"Nickname": "name_4",
"CreateTime": "2018-10-24 10:00:00"
},
{
"Id": 5,
"Passport": "user_5",
"Password": "",
"Nickname": "name_5",
"CreateTime": "2018-10-24 10:00:00"
},
{
"Id": 6,
"Passport": "user_6",
"Password": "",
"Nickname": "name_6",
"CreateTime": "2018-10-24 10:00:00"
},
{
"Id": 7,
"Passport": "user_7",
"Password": "",
"Nickname": "name_7",
"CreateTime": "2018-10-24 10:00:00"
},
{
"Id": 8,
"Passport": "user_8",
"Password": "",
"Nickname": "name_8",
"CreateTime": "2018-10-24 10:00:00"
},
{
"Id": 9,
"Passport": "user_9",
"Password": "",
"Nickname": "name_9",
"CreateTime": "2018-10-24 10:00:00"
},
{
"Id": 10,
"Passport": "user_10",
"Password": "",
"Nickname": "name_10",
"CreateTime": "2018-10-24 10:00:00"
}
] |
Tip |
---|
可以看到自定义的 |
2、自定义二进制TCP数据解包
一个TCP通信的数据包解包示例。
package main
import (
"errors"
"fmt"
"github.com/gogf/gf/crypto/gcrc32"
"github.com/gogf/gf/encoding/gbinary"
"github.com/gogf/gf/util/gconv"
)
type Pkg struct {
Length uint16 // Total length.
Crc32 uint32 // CRC32.
Data []byte
}
// NewPkg creates and returns a package with given data.
func NewPkg(data []byte) *Pkg {
return &Pkg{
Length: uint16(len(data) + 6),
Crc32: gcrc32.Encrypt(data),
Data: data,
}
}
// Marshal encodes the protocol struct to bytes.
func (p *Pkg) Marshal() []byte {
b := make([]byte, 6+len(p.Data))
copy(b, gbinary.EncodeUint16(p.Length))
copy(b[2:], gbinary.EncodeUint32(p.Crc32))
copy(b[6:], p.Data)
return b
}
// UnmarshalValue decodes bytes to protocol struct.
func (p *Pkg) UnmarshalValue(v interface{}) error {
b := gconv.Bytes(v)
if len(b) < 6 {
return errors.New("invalid package length")
}
p.Length = gbinary.DecodeToUint16(b[:2])
if len(b) < int(p.Length) {
return errors.New("invalid data length")
}
p.Crc32 = gbinary.DecodeToUint32(b[2:6])
p.Data = b[6:]
if gcrc32.Encrypt(p.Data) != p.Crc32 {
return errors.New("crc32 validation failed")
}
return nil
}
func main() {
var p1, p2 *Pkg
// Create a demo pkg as p1.
p1 = NewPkg([]byte("123"))
fmt.Println(p1)
// Convert bytes from p1 to p2 using gconv.Struct.
err := gconv.Struct(p1.Marshal(), &p2)
if err != nil {
panic(err)
}
fmt.Println(p2)
}
执行后,终端输出:
&{9 2286445522 [49 50 51]}
&{9 2286445522 [49 50 51]}
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