将查询结果从结构转换为另一个Golang包的字符串

I have searched for a solution on the net and in SO, but found nothing that apply to return values. It is a simple sql query with several rows that I want to return. Error handling not included:

func Fetch(query string) (string) {

    type User struct{
        id string
        name string
    }

    rows, err := db.Query(query)

    users := make([]*User, 0)
    for rows.Next() {
      user := new(User)
      err := rows.Scan(&user.id, &user.name)
      users = append(users, user)
    }

    return(users)
}

I get this error when compiling:

cannot use users (type []*User) as type string in return argument

How should I do to get a correct return value?

The expected input is

JD John Doe --OR-- {id:"JD",name:"John Doe"}

If you have to return a String you can use the encoding/json package to serialize your user object, but you have to use fields that begin with capital letters for them to be exported. See the full example:

import (
    "encoding/json"
)

func Fetch(query string) (string) {

    type User struct{
        Id string  // <-- CHANGED THIS LINE
        Name string // <-- CHANGED THIS LINE
    }

    rows, err := db.Query(query)

    users := make([]*User, 0)
    for rows.Next() {
      user := new(User)
      err := rows.Scan(&user.id, &user.name)
      users = append(users, user)
    }

    return(ToJSON(users)) // <-- CHANGED THIS LINE
}

func ToJSON(obj interface{}) (string) {
    res, err := json.Marshal(obj)
    if err != nil {
      panic("error with json serialization " + err.Error())
    }
    return string(res)
}

Add this to your code:

type userSlice []*User

func (us userSlice) String() string{
    var s []string
    for _, u := range us {
        if u != nil {
            s = append(s, fmt.Sprintf("%s %s", u.id, u.name))
        }
    }
    return strings.Join(s, "
")
}

type User struct{
  id string
  name string
}

In your Fetch function replace the last return statement like this:

func Fetch(query string) (string) {
  // Note that we declare the User type outside the function.
  rows, err := db.Query(query)

  users := make([]*User, 0)
  for rows.Next() {
    user := new(User)
    err := rows.Scan(&user.id, &user.name)
    users = append(users, user)
  }

  return(userSlice(users).String()) // Replace this line in your code
}