initial commit

cmd/list/main.go

@@ -0,0 +1,59 @@
+package main
+
+import (
+	"database/sql"
+	"flag"
+	"fmt"
+	"log"
+
+	"encoding/json"
+
+	_ "github.com/go-sql-driver/mysql"
+)
+
+var (
+	dbURL = flag.String("db", "julian:hi@/test", "The Database")
+)
+
+func main() {
+	flag.Parse()
+
+	db, err := sql.Open("mysql", *dbURL)
+	if err != nil {
+		log.Fatal(err)
+	}
+	if err = readStudiengaenge(db); err != nil {
+		log.Fatal("readStudiengaenge:", err)
+	}
+
+	result, err := db.Query("SELECT Vorname, Nachname, Matrnr, Studiengang FROM Teilnehmer")
+	if err != nil {
+		log.Fatal("error fetching students:", err)
+	}
+
+	var (
+		stud Student
+		ID   int
+	)
+
+	for result.Next() {
+		if err = result.Scan(&stud.Vorname, &stud.Nachname, &stud.Matrnr, &ID); err != nil {
+			log.Println("could not retrieve Student:", err)
+			continue
+		}
+
+		name, ok := studiengaenge[ID]
+		if !ok {
+			log.Println("illegal Studiengang:", ID)
+			continue
+		}
+
+		stud.Studiengang = name
+
+		out, err := json.Marshal(stud)
+		if err != nil {
+			log.Fatal("could not marshal to json:", err)
+		}
+		fmt.Println(string(out))
+	}
+}

cmd/list/studenten.go

@@ -0,0 +1,17 @@
+package main
+
+import (
+	"strconv"
+)
+
+// Ein Student
+type Student struct {
+	Vorname, Nachname string
+	Matrnr            int
+	Studiengang       Studiengang
+}
+
+// Gibt den Studenten als String zurück
+func (s Student) String() string {
+	return "{" + strconv.Itoa(s.Matrnr) + " " + s.Nachname + ", " + s.Vorname + " \"" + *s.Studiengang + "\"}"
+}

cmd/list/studiengang.go

@@ -0,0 +1,32 @@
+package main
+
+import "database/sql"
+
+// Ein Studiengang
+type Studiengang *string
+
+// globale Tabelle aller Studiengänge
+var studiengaenge map[int]Studiengang
+
+// lese alle Studiengänge aus der mysql Tabelle
+func readStudiengaenge(db *sql.DB) error {
+	studiengaenge = make(map[int]Studiengang)
+	result, err := db.Query("SELECT ID, Studiengaenge.Name FROM Studiengaenge")
+	if err != nil {
+		return err
+	}
+
+	var (
+		ID   int
+		stud string
+	)
+
+	for result.Next() {
+		if err = result.Scan(&ID, &stud); err != nil {
+			return err
+		}
+		studiengaenge[ID] = Studiengang(&stud)
+	}
+
+	return nil
+}