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私は、Preload（）の代わりにSQL結合を使用してアプリケーションを最適化しようとしています。 しかし、私はモデルの結合されたテーブルが常に空である問題に遭遇しました。Gormはモデルへの結合を結合しません
私は新しいプロジェクトを開いていくつかの簡単なサンプルコードと同じ問題を発見しました。 以下のコードを実行すると、結合テーブルは常に空の配列になります。
私は何か間違っていますか？
import (
"fmt"
"log"
"github.com/jinzhu/gorm"
_ "github.com/lib/pq"
)
type Language struct {
ID uint `gorm:"primary_key"`
Name string
}
type Movie struct {
ID uint `gorm:"primary_key"`
Title string
Language Language
LanguageID uint
}
type Artist struct {
ID uint `gorm:"primary_key"`
Name string
Movies []Movie `gorm:"many2many:artist_movies"`
}
func createArtists() {
langs := []Language{{Name: "english"},
{Name: "tamil"},
{Name: "french"}}
for i, _ := range langs {
if err := db.Create(&langs[i]).Error; err != nil {
log.Fatal(err)
}
}
movies := []Movie{
{Title: "Nayagan", Language: langs[1]},
{Title: "Anbe sivam", Language: langs[1]},
{Title: "3 idiots", Language: langs[2]},
{Title: "Shamithab", Language: langs[2]},
{Title: "Dark Knight", Language: langs[0]},
{Title: "310 to Yuma", Language: langs[0]},
}
for i, _ := range movies {
if err := db.Create(&movies[i]).Error; err != nil {
log.Fatal(err)
}
}
artists := []Artist{
{Name: "Madhavan", Movies: []Movie{movies[1],movies[2]}},
{Name: "Kamal Hassan", Movies: []Movie{movies[0], movies[1]}},
{Name: "Dhanush", Movies: []Movie{movies[3]}},
{Name: "Aamir Khan", Movies: []Movie{movies[2]}},
{Name: "Amitabh Bachchan", Movies: []Movie{movies[3]}},
{Name: "Christian Bale", Movies: []Movie{movies[4], movies[5]}},
{Name: "Russell Crowe", Movies: []Movie{movies[5]}},
}
for i, _ := range artists {
if err := db.Create(&artists[i]).Error; err != nil {
log.Fatal(err)
}
}
}
var db *gorm.DB
func main() {
var err error
db, err = gorm.Open("postgres", "user=admin password=1234 dbname=test sslmode=disable")
if err != nil {
log.Fatal(err)
}
db.AutoMigrate(new(Language), new(Movie), new(Artist))
db.LogMode(true)
createArtists()
var artists []Artist
if err = db.Joins("JOIN artist_movies on artist_movies.artist_id=artists.id").
Joins("JOIN movies on movies.id=artist_movies.movie_id").
Joins("JOIN languages on movies.language_id=languages.id").
Where("languages.name=?", "tamil").
Group("artists.id").Find(&artists).Error; err != nil {
log.Fatal(err)
}
for _, ar := range artists {
fmt.Println(ar.Movies)
}
artists = []Artist{}
if err = db.Joins("JOIN artist_movies on artist_movies.artist_id=artists.id").
Joins("JOIN movies on artist_movies.movie_id=movies.id").Where("movies.title=?", "Nayagan").
Group("artists.id").Find(&artists).Error; err != nil {
log.Fatal(err)
}
for _, ar := range artists {
fmt.Println(ar.Movies)
}
artists = []Artist{}
if err = db.Joins("JOIN artist_movies on artist_movies.artist_id=artists.id").
Joins("JOIN movies on artist_movies.movie_id=movies.id").
Where("movies.title in (?)", []string{"3 idiots", "Shamitabh", "310 to Yuma"}).
Group("artists.id").Find(&artists).Error; err != nil {
log.Fatal(err)
}
for _, ar := range artists {
fmt.Println(ar.Movies)
}
}