SELECT导致的Golang Gorp错误

Question

I am trying to do a SELECT from mySQL database with GORP. I am getting an error which says "reflect.Value.Interface: cannot return value obtained from unexported field or method". I have verified the DB connectivity. For example Select (*) count gives the right count. I see that it fails on

dbmap.Select(&dd, "SELECT * FROM kd_dropdowns")

Without the above line program does not throw any error.

Here is my code.

package main
import (
"database/sql"
"fmt"
"log"
"net/http"

"github.com/coopernurse/gorp"
_ "github.com/go-sql-driver/mysql"
"github.com/gorilla/mux"
)

func main() {

fmt.Println("reached main")
// Create a MUX
r := mux.NewRouter()

//manegala patti
r.HandleFunc("/manegalu", manegalaTorisu).Methods("GET")

http.ListenAndServe(":8080", r)

}
func manegalaTorisu(w http.ResponseWriter, r *http.Request) {
type Dropdowns struct {
    dd_id      int64  `db:"dd_id"`
    identifier int64  `db:"identifier"`
    name       string `db:"name"`
    active     string `db:"active"`
}

db, err := sql.Open("mysql", "krishna:xxxx@/kd")
defer db.Close()

var dbmap *gorp.DbMap
// construct a gorp DbMap
dbmap = &gorp.DbMap{Db: db, Dialect: gorp.MySQLDialect{}}

var dd []Dropdowns
_, err = dbmap.Select(&dd, "SELECT * FROM kd_dropdowns")
checkErr(err, "Select failed")
fmt.Fprint(w, "Success")
}

func checkErr(err error, msg string) {
if err != nil {
    log.Fatalln(msg, err)
}
}

Answer 1

This is a common trap for people starting with Go.

All the fields in a struct are exported or hidden simply based on the first letter: if it is uppercase, the field is exported. Otherwise, it is not.

Gorp is trying to access the exported fields in your struct. But you've used lowercase first-letters, so the fields are hidden and so it fails.

Try this instead.

...
type Dropdowns struct {
    DdId       int64  `db:"dd_id"`
    Identifier int64  `db:"identifier"`
    Name       string `db:"name"`
    Active     string `db:"active"`
}
...

You can camelcase your dd_id as DdId if you prefer (I think this is more idiomatic in Go).

Note that the uppercase export feature of Go applies to constants, package variables, types and function names, as well as the fields within structs.