我有一个由几个结构组成的层次
type Entry struct {
Id int
CreatedAt time.Time
UpdatedAt time.Time
Fields []Field
}
type SyncField struct {
Id int
CreatedAt time.Time
UpdatedAt time.Time
TechnicalName string
JsonName string
EntryId int
Decorators []Decorator
}
type Decorator struct {
Id int
CreatedAt time.Time
UpdatedAt time.Time
Name string
Description string
SortingOrder int
Params string
SyncFieldId int
}
我的数据库创建方式如下：
db.CreateTable(&Entry{})
db.CreateTable(&SyncField{})
db.Model(&Entry{}).Related(&SyncField{}, "EntryId")
db.CreateTable(&Decorator{})
db.Model(&SyncField{}).Related(&Decorator{}, "DecoratorId")
一切都很清楚，只能预加载这样的层次结构中的一个“子级别”：
entry := &Entry{Id: i}
iDB.Preload("SyncFields").First(entry)
或
field := &SyncField{Id: idf}
iDB.Preload("Decorators").First(field)
我正在寻找一种方法，使用GORM预加载整个层次，在其中一个根元素上调用“First（）”方法... 我想加载一个带有所有相关“字段”的“条目”，我也希望每个“字段”预装所有“装饰器”......
使用几个“Preload（）”函数是不可行的：
entry := &Entry{Id: i}
iDB.Preload("Decorators").Preload("SyncFields").First(entry)
我理解“iDB.Preload("child1").Preload("child2").First(root)”在child1和child2都是root的“叶子”时都有效。
所以我的问题是：是否有可能使用gorm执行此操作，如果是，以递归方式加载comlete层次结构的最佳方法是什么？
感谢。 此致
答案 0 :(得分：8)
答案 1 :(得分：2)
我的解决方案：
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package main
/// http://stackoverflow.com/questions/23030884/is-there-a-way-to-create-an-instance-of-a-struct-from-a-string
/// http://stackoverflow.com/questions/7850140/how-do-you-create-a-new-instance-of-a-struct-from-its-type-at-runtime-in-go
/// http://stackoverflow.com/questions/29435783/gorm-golang-orm-associations
import (
"github.com/jinzhu/gorm"
_ "github.com/jinzhu/gorm/dialects/sqlite"
"fmt"
"reflect"
"regexp"
"encoding/json"
"encoding/xml"
//"strconv"
"os"
"flag"
"strings"
)
type rs struct {
//Parent *rs `gorm:"ForeignKey:ID;AssociationForeignKey:ParentID"`
Childs []*rs `gorm:"ForeignKey:ID;AssociationForeignKey:ParentID" walkrec:"true"`
ID int64
ParentID int64 `gorm:"column:ParentID"`
Value string
Sub []rs_sub `gorm:"ForeignKey:ID;AssociationForeignKey:Rs_ID" walkrec:"true"`
}
type rs_sub struct {
ID int64
Rs_ID int64 `gorm:"column:rs_id"`
Value string
}
var db *gorm.DB
func populateDb(db *gorm.DB) {
rs1 := rs{ID: 1, ParentID: 0, Value: "root"}
db.Save(&rs1)
rs2 := rs{ID: 2, ParentID: 1, Value: "Child1"}
db.Save(&rs2)
rs3 := rs{ID: 3, ParentID: 2, Value: "Child2"}
db.Save(&rs3)
rs4 := rs{ID: 4, ParentID: 3, Value: "Child3"}
db.Save(&rs4)
rs5 := rs{ID: 5, ParentID: 3, Value: "Child4"}
db.Save(&rs5)
rs_s := rs_sub{ID:1, Rs_ID:4, Value: "SubChild1"}
db.Save(&rs_s)
}
func PStdErr(format string, args ...interface{}) {
fmt.Fprintf(os.Stderr, format, args...)
}
func JsonMarshal(data interface{}) string {
b, err := json.Marshal(data)
if err != nil {
return "Error"
}
return string(b[:])
}
func XmlMarshal(data interface{}) string {
b, err := xml.Marshal(data)
if err != nil {
return "Error"
}
return string(b[:])
}
func InitDB() *gorm.DB {
db, err := gorm.Open("sqlite3", ":memory:")
if err != nil {
panic("failed to connect database")
}
db.Exec("DROP TABLE IF EXISTS rs;")
db.SingularTable(true)
// Migrate the schema
db.AutoMigrate(&rs{})
db.AutoMigrate(&rs_sub{})
populateDb(db)
//db.LogMode(true)
return db
}
// This function fetches all related objects from a given object in the data parameter.
// The struct must be fully tagged, we don't recognize automatically related IDs and so on.
// The function works only with not combined keys.
// Every field which should be fetched must be tagged with:
// walkrec:"true" gorm:"ForeignKey:ID;AssociationForeignKey:ForeignKey"
// See: http://stackoverflow.com/questions/24537525/reflect-value-fieldbyname-causing-panic
// See: http://stackoverflow.com/questions/34493062/how-to-reflect-struct-recursive-in-golang
func fetchRec(db *gorm.DB, data interface{}) {
// With data *rs: Type: *main.rs
// With data interface{}: *main.rs
var ref reflect.Value
if reflect.TypeOf(data).Kind() == reflect.Struct {
ref = reflect.ValueOf(data)
} else if reflect.TypeOf(data).Kind() == reflect.Ptr {
ref = reflect.Indirect(reflect.ValueOf(data))
}
if ref.Type().Kind() == reflect.Slice {
for i := 0; i < ref.Len(); i++ {
if ref.Index(i).Type().Kind() == reflect.Ptr {
fetchRec(db, ref.Index(i).Elem().Addr().Interface())
} else if ref.Index(i).Type().Kind() == reflect.Struct {
// What should we do here?
}
}
} else if ref.Type().Kind() == reflect.Struct {
for i := 0; i < ref.NumField(); i++ {
var IDFieldRaw string
var IDFields []string
var RefFieldRaw string
var RefFields []string
var re *regexp.Regexp
var matches []string
if ref.Field(i).CanAddr() && strings.EqualFold(ref.Type().Field(i).Tag.Get("walkrec"), "true") {
gormflags := ref.Type().Field(i).Tag.Get("gorm")
if gormflags == "" {
panic("No gorm flags found!")
} else {
re = regexp.MustCompile(`\bForeignKey:([a-zA-Z0-9_,]+)\b`)
matches = re.FindStringSubmatch(gormflags)
if len(matches) == 2 {
IDFieldRaw = matches[1]
IDFields = strings.Split(IDFieldRaw, ",")
}
re = regexp.MustCompile(`\bAssociationForeignKey:([a-zA-Z0-9_,]+)\b`)
matches = re.FindStringSubmatch(gormflags)
if len(matches) == 2 {
RefFieldRaw = matches[1]
RefFields = strings.Split(RefFieldRaw, ",")
}
}
if len(IDFields) == 0 { continue }
if len(RefFields) != 0 {
WhereMap := make(map[string]interface{})
for fk := 0; fk < len(RefFields); fk++ {
WhereMap[RefFields[fk]] = fmt.Sprint(ref.FieldByName(IDFields[fk]))
}
db.Where(WhereMap).Find(ref.Field(i).Addr().Interface())
if ref.Field(i).Addr().Interface() != nil {
fetchRec(db, ref.Field(i).Addr().Interface())
}
} else {
panic("AssociationForeignKey empty!")
}
}
}
}
}
func getParams() (id int) {
flag.IntVar(&id, "id", 1, "the id to fetch")
flag.Parse()
return
}
func fetch(db *gorm.DB, id interface{}) (d rs, found bool) {
//db.First(&d, id)
found = false
found = !db.Find(&d, id).RecordNotFound()
if found {
fetchRec(db, &d)
}
return
}
// Execute this program. For example:
// go run main.go --id=2
func main() {
db = InitDB()
defer db.Close()
id := getParams()
PStdErr("Loading data with ID %d\n", id)
rs, found := fetch(db, id)
if found {
fmt.Print(XmlMarshal(rs) + "\n")
}
}