Reflecting The Fields of a Empty's Slices Underyling Type?

I have the following query builder function:

func CreateQuery(t interface{}, where string) {
	var b bytes.Buffer
	b.WriteString("SELECT ")
	
	s := reflect.ValueOf(t).Elem()
	typeOfT := s.Type()
	
	for i := 0; i < s.NumField() - 1; i++ {
		b.WriteString(fmt.Sprintf("%s, ", typeOfT.Field(i).Name))
	}
	
	//Last one has no Comma
	b.WriteString(fmt.Sprintf("%s ", typeOfT.Field(s.NumField() - 1).Name))
	
	b.WriteString(fmt.Sprintf("FROM %s ", typeOfT.Name()))
	b.WriteString(where)
	fmt.Println(b.String())
}

There works fine when called as follows:

var dst FooStruct
CreateQuery(&dst, "")

But the following raises a "call of reflect.Value.NumField on slice Value" Panic:

var dst []FooStruct
CreateQuery(&dst, "")

How I can I make the function print the fields of a slice's underlying struct type? It seems like I want the inverse of reflect's SliceOf function.

You can only call NumField or Field methods on a reflect.Type representing a struct (i.e. t.Kind() == reflect.Struct).

If you have a slice type, you can access the contained type via the Elem method, which returns another reflect.Type. If the slice contains a struct, then you can call NumField/Field on this type.

You can iterate over the slice, calling CreateQuery for every query:

func CreateQueries(t interface{}, where string) {
	v := reflect.ValueOf(t)

	if v.Kind() == reflect.Ptr {
		v = v.Elem()
	}

	if v.Kind() == reflect.Array || v.Kind() == reflect.Slice {
		for i := 0; i < v.Len(); i++ {
			CreateQuery(v.Index(i).Interface(), where)
		}
	}
}

Using reflect.Value.Index you can access each field separately, calling .Interface() on the
value yields the interface{} type representation of that value, making it suitable to put
it in your CreateQuery function (which expects a interface{} value).