Serializer

Serializer is an extensible interface that allows to customize how to serialize and deserialize data with databasae.

GORM provides some default serializers: json, gob, unixtime, here is a quick example of how to use it.

type User struct {
Name []byte `gorm:"serializer:json"`
Roles Roles `gorm:"serializer:json"`
Contracts map[string]interface{} `gorm:"serializer:json"`
JobInfo Job `gorm:"type:bytes;serializer:gob"`
CreatedTime int64 `gorm:"serializer:unixtime;type:time"` // store int as datetime into database
}

type Roles []string

type Job struct {
Title string
Location string
IsIntern bool
}

createdAt := time.Date(2020, 1, 1, 0, 8, 0, 0, time.UTC)
data := User{
Name: []byte("jinzhu"),
Roles: []string{"admin", "owner"},
Contracts: map[string]interface{}{"name": "jinzhu", "age": 10},
CreatedTime: createdAt.Unix(),
JobInfo: Job{
Title: "Developer",
Location: "NY",
IsIntern: false,
},
}

DB.Create(&data)
// INSERT INTO `users` (`name`,`roles`,`contracts`,`job_info`,`created_time`) VALUES
// ("\"amluemh1\"","[\"admin\",\"owner\"]","{\"age\":10,\"name\":\"jinzhu\"}",<gob binary>,"2020-01-01 00:08:00")

var result User
DB.First(&result, "id = ?", data.ID)
// result => User{
// Name: []byte("jinzhu"),
// Roles: []string{"admin", "owner"},
// Contracts: map[string]interface{}{"name": "jinzhu", "age": 10},
// CreatedTime: createdAt.Unix(),
// JobInfo: Job{
// Title: "Developer",
// Location: "NY",
// IsIntern: false,
// },
// }

DB.Where(User{Name: []byte("jinzhu")}).Take(&result)
// SELECT * FROM `users` WHERE `users`.`name` = "\"amluemh1\"

Register Serializer

A Serializer needs to implement how to serialize and deserialize data, so it requires to implement the the following interface

import "gorm.io/gorm/schema"

type SerializerInterface interface {
Scan(ctx context.Context, field *schema.Field, dst reflect.Value, dbValue interface{}) error
SerializerValuerInterface
}

type SerializerValuerInterface interface {
Value(ctx context.Context, field *schema.Field, dst reflect.Value, fieldValue interface{}) (interface{}, error)
}

For example, the default JSONSerializer is implemented like:

// JSONSerializer json serializer
type JSONSerializer struct {
}

// Scan implements serializer interface
func (JSONSerializer) Scan(ctx context.Context, field *Field, dst reflect.Value, dbValue interface{}) (err error) {
fieldValue := reflect.New(field.FieldType)

if dbValue != nil {
var bytes []byte
switch v := dbValue.(type) {
case []byte:
bytes = v
case string:
bytes = []byte(v)
default:
return fmt.Errorf("failed to unmarshal JSONB value: %#v", dbValue)
}

err = json.Unmarshal(bytes, fieldValue.Interface())
}

field.ReflectValueOf(ctx, dst).Set(fieldValue.Elem())
return
}

// Value implements serializer interface
func (JSONSerializer) Value(ctx context.Context, field *Field, dst reflect.Value, fieldValue interface{}) (interface{}, error) {
return json.Marshal(fieldValue)
}

And registered with the following code:

schema.RegisterSerializer("json", JSONSerializer{})

After registering a serializer, you can use it with the serializer tag, for example:

type User struct {
Name []byte `gorm:"serializer:json"`
}

Customized Serializer Type

You can use a registered serializer with tags, you are also allowed to create a customized struct that implements the above SerializerInterface and use it as a field type directly, for example:

type EncryptedString string

// ctx: contains request-scoped values
// field: the field using the serializer, contains GORM settings, struct tags
// dst: current model value, `user` in the below example
// dbValue: current field's value in database
func (es *EncryptedString) Scan(ctx context.Context, field *schema.Field, dst reflect.Value, dbValue interface{}) (err error) {
switch value := dbValue.(type) {
case []byte:
*es = EncryptedString(bytes.TrimPrefix(value, []byte("hello")))
case string:
*es = EncryptedString(strings.TrimPrefix(value, "hello"))
default:
return fmt.Errorf("unsupported data %#v", dbValue)
}
return nil
}

// ctx: contains request-scoped values
// field: the field using the serializer, contains GORM settings, struct tags
// dst: current model value, `user` in the below example
// fieldValue: current field's value of the dst
func (es EncryptedString) Value(ctx context.Context, field *schema.Field, dst reflect.Value, fieldValue interface{}) (interface{}, error) {
return "hello" + string(es), nil
}

type User struct {
gorm.Model
Password EncryptedString
}

data := User{
Password: EncryptedString("pass"),
}

DB.Create(&data)
// INSERT INTO `serializer_structs` (`password`) VALUES ("hellopass")

var result User
DB.First(&result, "id = ?", data.ID)
// result => User{
// Password: EncryptedString("pass"),
// }

DB.Where(User{Password: EncryptedString("pass")}).Take(&result)
// SELECT * FROM `users` WHERE `users`.`password` = "hellopass"

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