我的解决方案：
/****** MIT License **********
Copyright (c) 2017 Zonkiie
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
***************************/
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")
}
}