Gorm 插件在多语言重构应用
现状：项目内有很多Movie表相关的查询，包括单条数据查询，列表查询和各种连表查询 需要支持 Movie表 的多语言
- 直接修改原查询
Movie表代码改动过大，使用gorm的插件来支持语言的切换 - 根据前端的 header Accept-Language 判断需要返回什么语言
Gorm 插件
此处参考gorm官方文档：https://gorm.io/zh_CN/docs/write_plugins.html#Registering-a-Plugin
go
type TranslationPlugin struct{}
func (p *TranslationPlugin) Name() string {
return "TranslationPlugin"
}
func (p *TranslationPlugin) Initialize(db *gorm.DB) error {
db.Callback().Query().After("gorm:after_query").Register("translation:load_translations", p.loadTranslations)
return nil
}
func (p *TranslationPlugin) loadTranslations(db *gorm.DB) {
... // todo
}实现 loadTranslations
go
func (p *TranslationPlugin) loadTranslations(db *gorm.DB) {
if db.Statement.Schema.Table == "movie_table" {
language, ok := db.Statement.Context.Value(LanguageContextKey).(string)
if !ok || db.Statement.Schema == nil {
return
}
var movies []models.Movie
switch t := db.Statement.Model.(type) {
case *[]models.Movie:
movies = *t
case *[]*models.Movie:
for _, m := range *t {
movies = append(movies, *m)
}
default:
return
}
// 覆盖电影的 title 和 overview
for i, _ := range movies {
movies[i].Title = "translation.Title" + strconv.Itoa(i)
movies[i].Overview = "translation.Overview" + strconv.Itoa(i)
}
// 更新 db.Statement.Model 为修改后的 movies
db.Statement.ReflectValue.Set(reflect.ValueOf(movies))
return
}}上面的实现支持了Movie对象的赋值，但是查询movie表的返回用到了很多不同的对象接收
这里如果每个对象都判断再赋值会导致switch case块过长，逻辑过于冗长，故而牺牲了一些性能使用反射处理
golang 反射使用
[12.Golang 反射性能优化.md](12.Golang 反射性能优化.md)
go
func setFieldValue(structValue reflect.Value, fieldName, newValue string) {
field := structValue.FieldByName(fieldName)
if field.IsValid() && field.CanSet() && field.Kind() == reflect.String {
field.SetString(newValue)
}
}
func getFieldValue(structValue reflect.Value, fieldName string) int64 {
field := structValue.FieldByName(fieldName)
if field.IsValid() && field.Kind() == reflect.Int64 {
return field.Int()
}
return 0
}完整 testcase 示例
go
package movie_service
import (
"context"
"xxx/models"
"xxx/models/enums"
"xxx/models/params/res"
"fmt"
"gorm.io/driver/postgres"
"gorm.io/gorm"
"reflect"
"strconv"
"testing"
)
type TranslationContextKey string
const LanguageContextKey TranslationContextKey = "language"
type TranslationPlugin struct{}
func (p *TranslationPlugin) Name() string {
return "TranslationPlugin"
}
func (p *TranslationPlugin) Initialize(db *gorm.DB) error {
db.Callback().Query().After("gorm:after_query").Register("translation:load_translations", p.loadTranslations)
return nil
}
func (p *TranslationPlugin) loadTranslations(db *gorm.DB) {
language, ok := db.Statement.Context.Value(LanguageContextKey).(string)
fmt.Println(language)
if !ok || db.Statement.Schema == nil {
return
}
if db.Statement.Schema.Table == "movie_table" {
fmt.Println("SQL:", db.Statement.SQL.String())
modelValue := reflect.ValueOf(db.Statement.Model)
modelValue = dereferenceIfNeeded(modelValue)
if modelValue.Kind() == reflect.Slice {
// Traverse the slice and modify fields
for i := 0; i < modelValue.Len(); i++ {
item := modelValue.Index(i)
item = dereferenceIfNeeded(item)
if item.Kind() == reflect.Struct {
modifyFields(item, language)
}
}
} else if modelValue.Kind() == reflect.Pointer {
item := dereferenceIfNeeded(modelValue)
if item.Kind() == reflect.Struct {
modifyFields(item, language)
}
}
}
}
func modifyFields(structValue reflect.Value, language string) {
structValue = dereferenceIfNeeded(structValue)
id := getFieldValue(structValue, "ID")
setFieldValue(structValue, "Title", getTitleByID(id, language))
setFieldValue(structValue, "Overview", getOverviewByID(id, language))
}
func getTitleByID(id int64, language string) string {
return "func => query from db: translation.Title_" + language + strconv.Itoa(int(id))
}
func getOverviewByID(id int64, language string) string {
return "func => query from db: translation.Overview_" + language + strconv.Itoa(int(id))
}
func setFieldValue(structValue reflect.Value, fieldName, newValue string) {
field := structValue.FieldByName(fieldName)
if field.IsValid() && field.CanSet() && field.Kind() == reflect.String {
field.SetString(newValue)
}
}
func getFieldValue(structValue reflect.Value, fieldName string) int64 {
field := structValue.FieldByName(fieldName)
if field.IsValid() && field.Kind() == reflect.Int64 {
return field.Int()
}
return 0
}
func dereferenceIfNeeded(value reflect.Value) reflect.Value {
if value.Kind() == reflect.Ptr {
if value.IsNil() {
return reflect.Zero(value.Type().Elem())
}
return value.Elem()
}
return value
}
func TestPlugin(t *testing.T) {
dsn := fmt.Sprintf("host=%s user=%s password=%s dbname=%s port=%s sslmode=disable TimeZone=UTC",
"xxx",
"xxx",
"xxx",
"xxx",
"5432")
db, err := gorm.Open(postgres.Open(dsn), &gorm.Config{})
if err != nil {
panic("failed to connect database")
}
if err := db.Use(&TranslationPlugin{}); err != nil {
panic("failed use TranslationPlugin")
}
ctx := context.WithValue(context.Background(), LanguageContextKey, "en")
var movie *models.Movie
tx := db.Debug().WithContext(ctx).Limit(1).First(&movie)
if tx.Error != nil {
fmt.Println(tx.Error)
} else {
fmt.Println(movie)
}
var movies []*res.MovieInfoForVodRes
title := "A"
err = db.WithContext(ctx).Table("movie_table m").
Select("DISTINCT m.*, cover.url as cover, poster.url as poster, p.is_offline").
Joins("INNER JOIN license_table l on m.id=l.movie_id").
Joins("LEFT JOIN product_table p ON p.source_id = l.id and p.source_type=1").
Joins("LEFT JOIN movie_alternative_title_table malt on m.id = malt.movie_id").
Joins("LEFT JOIN movie_images_table cover on cover.movie_id=m.id AND cover.is_movie_cover=true").
Joins("LEFT JOIN movie_images_table poster on poster.movie_id=m.id AND poster.is_movie_poster=true").
Where("m.type =? AND (malt.title ILIKE ? OR m.title ILIKE ?)", enums.TVShow, "%"+title+"%", "%"+title+"%").
Limit(10).Offset(0).Find(&movies).Error
if err != nil {
fmt.Println(err)
} else {
for _, movie := range movies {
fmt.Printf("%+v\n", movie)
}
}
var movies2 []*models.Movie
err = db.Debug().WithContext(ctx).Limit(5).Find(&movies2).Error
if err != nil {
fmt.Println(err)
} else {
for _, movie := range movies2 {
fmt.Printf("%+v\n", movie)
}
}
}