Golang - MongoDB (mgo) retrieve inserted file (BSON not GridFS) - mongodb

Question

I am a newbie in Golang.
I am trying to retrieve a PDF file object I have inserted. I am not using GridFS, as the files that I would be storing are under 16 MB.
The object has been inserted (using load_file function) and the object ID I am seeing with the MongoDB visual client is ObjectId("554f98a400afc2dd3cbfb21b").
Unfortunately the file created on disk is of 0 kb.
Please advise how to correctly retrieve the inserted PDF object.
Thank you
package main
import (
"fmt"
"io/ioutil"
"gopkg.in/mgo.v2"
)
type Raw struct {
Kind byte
Data []byte
}
type RawDocElem struct {
Name string
Value Raw
}
func check(err error) {
if err != nil {
panic(err.Error())
}
}
func read_file_content(AFileName string) []byte {
file_contents, err := ioutil.ReadFile(AFileName)
check(err)
return file_contents
}
func save_fetched_file(AFileName RawDocElem) {
ioutil.WriteFile("fisier.pdf", AFileName.Value.Data, 0644)
fmt.Println("FileName:", AFileName.Name)
}
func load_file(AFileName string, ADatabaseName string, ACollection string) {
session, err := mgo.Dial("127.0.0.1,127.0.0.1")
if err != nil {
panic(err)
}
defer session.Close()
session.SetMode(mgo.Monotonic, true)
c := session.DB(ADatabaseName).C(ACollection)
the_obj_to_insert := Raw{Kind: 0x00, Data: read_file_content(AFileName)}
err = c.Database.C(ACollection).Insert(&the_obj_to_insert)
check(err)
}
func get_file(ADatabaseName string, ACollection string, The_ID string) RawDocElem {
session, err := mgo.Dial("127.0.0.1,127.0.0.1")
if err != nil {
panic(err)
}
defer session.Close()
session.SetMode(mgo.Monotonic, true)
c := session.DB(ADatabaseName).C(ACollection)
result := RawDocElem{}
err = c.FindId(The_ID).One(&result)
return result
}
func main() {
//f_name := "Shortcuts.pdf"
db_name := "teste"
the_collection := "ColectiaDeFisiere"
//load_file(f_name, db_name, the_collection)
fmt.Sprintf(`ObjectIdHex("%x")`, string("554f98a400afc2dd3cbfb21b"))
save_fetched_file(get_file(db_name, the_collection, fmt.Sprintf(`ObjectIdHex("%x")`, string("554f98a400afc2dd3cbfb21b"))))
}

Answer 1

I think your way to build the object ID is wrong. Furthermore, you forgot to test the error following the FindId call.
I would try to import the bson package, and build the object ID using something like:
hexString := "554f98a400afc2dd3cbfb21b" //24 digits hexadecimal string
objid := bson.ObjectIdHex(hexString)
...
err = c.FindId(objid).One(&result)
if err == nil {
// Do something with result
...
} else {
// Error
...
}