diff --git a/php/model/DatabaseUserManager.php b/php/model/DatabaseUserManager.php
index bdbd120..a985160 100644
--- a/php/model/DatabaseUserManager.php
+++ b/php/model/DatabaseUserManager.php
@@ -5,58 +5,43 @@ require_once "UserManagerDAO.php";
 class DatabaseUserManager implements UserManagerDAO {
 
     private static $instance = null;
+
     public function __construct()
     {
+        try {
+            $db = $this->getConnection();
 
-        if (!file_exists(__DIR__ . '/../../db/users.db')) {
-            try {
-                $user = 'root';
-                $pw = null;
-                $dsn = 'sqlite:' . __DIR__ . '/../../db/users.db';
-
-                $db = new PDO($dsn, $user, $pw);
-
-                file_put_contents(
-                    __DIR__ . '/../../db/test.txt',
-                    'PDO funktioniert'
-                );
-
-                $db->exec("
-                CREATE TABLE users (
+            $db->exec("
+                CREATE TABLE IF NOT EXISTS users (
                     email TEXT PRIMARY KEY,
-                    vorname TEXT,
-                    nachname TEXT,
-                    password TEXT
+                    vorname TEXT NOT NULL,
+                    nachname TEXT NOT NULL,
+                    password TEXT NOT NULL
                 );
             ");
 
-                unset($db);
+            unset($db);
 
-            } catch (PDOException $e) {
-                throw new RuntimeException($e->getMessage());
-            }
+        } catch (PDOException $e) {
+            throw new RuntimeException("Benutzerdatenbank konnte nicht erstellt werden.");
         }
     }
-    /**
-     * Baut die Verbindung zur Datenbank auf.
-     */
+
     private function getConnection()
     {
         try {
-            $user = 'root';
-            $pw = null;
             $dsn = 'sqlite:' . __DIR__ . '/../../db/users.db';
 
-            return new PDO($dsn, $user, $pw);
+            $db = new PDO($dsn, null, null);
+            $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
+
+            return $db;
 
         } catch (PDOException $e) {
-            throw new RuntimeException($e->getMessage());
+            throw new RuntimeException("Verbindung zur Benutzerdatenbank fehlgeschlagen.");
         }
     }
 
-    /**
-     * Singleton-Instanz zurückgeben.
-     */
     public static function getInstance()
     {
         if (self::$instance == null) {
@@ -66,20 +51,14 @@ class DatabaseUserManager implements UserManagerDAO {
         return self::$instance;
     }
 
-
     public function findUser($email)
     {
         try {
             $db = $this->getConnection();
 
             $sql = "SELECT * FROM users WHERE email = :email";
-
             $command = $db->prepare($sql);
 
-            if (!$command) {
-                throw new RuntimeException("Benutzer konnte nicht geladen werden.");
-            }
-
             $command->execute([
                 ":email" => $email
             ]);
@@ -89,7 +68,7 @@ class DatabaseUserManager implements UserManagerDAO {
             return $user ?: null;
 
         } catch (PDOException $e) {
-            throw new RuntimeException($e->getMessage());
+            throw new RuntimeException("Benutzer konnte nicht geladen werden.");
         }
     }
 
@@ -97,90 +76,46 @@ class DatabaseUserManager implements UserManagerDAO {
     {
         try {
             $db = $this->getConnection();
-
             $db->beginTransaction();
 
-            $existingUser = $this->findUser($email);
-
-            if ($existingUser !== null) {
-                $db->rollBack();
-                throw new InvalidArgumentException(
-                    "Diese E-Mail-Adresse wird bereits verwendet."
-                );
-            }
-
             $sql = "
-                INSERT INTO users (
-                    email,
-                    vorname,
-                    nachname,
-                    password
-                )
-                VALUES (
-                    :email,
-                    :vorname,
-                    :nachname,
-                    :password
-                )
+                INSERT INTO users (email, vorname, nachname, password)
+                VALUES (:email, :vorname, :nachname, :password)
             ";
 
             $command = $db->prepare($sql);
 
-            if (!$command) {
-                $db->rollBack();
-                throw new RuntimeException(
-                    "Benutzer konnte nicht gespeichert werden."
-                );
-            }
-
-            $success = $command->execute([
+            $command->execute([
                 ":email" => $email,
                 ":vorname" => $vorname,
                 ":nachname" => $nachname,
                 ":password" => $password
             ]);
 
-            if (!$success) {
-                $db->rollBack();
-                throw new RuntimeException(
-                    "Benutzer konnte nicht gespeichert werden."
-                );
-            }
-
             $db->commit();
 
         } catch (PDOException $e) {
-            throw new RuntimeException($e->getMessage());
+            if (isset($db) && $db->inTransaction()) {
+                $db->rollBack();
+            }
+
+            if ($e->getCode() === "23000") {
+                throw new InvalidArgumentException("Diese E-Mail-Adresse wird bereits verwendet.");
+            }
+
+            throw new RuntimeException("Benutzer konnte nicht gespeichert werden.");
         }
     }
 
-    public function updateUser(
-        $oldEmail,
-        $newEmail,
-        $vorname,
-        $nachname,
-        $password = null
-    ) {
+    public function updateUser($oldEmail, $newEmail, $vorname, $nachname, $password = null)
+    {
         try {
             $db = $this->getConnection();
 
-            if ($oldEmail !== $newEmail) {
-
-                $existingUser = $this->findUser($newEmail);
-
-                if ($existingUser !== null) {
-                    throw new InvalidArgumentException(
-                        "Diese E-Mail-Adresse wird bereits verwendet."
-                    );
-                }
-            }
-
             if (!empty($password)) {
-
                 $sql = "
                     UPDATE users
-                    SET
-                        email = :newEmail,
+                    SET email = :newEmail,
                         vorname = :vorname,
                         nachname = :nachname,
                         password = :password
@@ -191,19 +126,13 @@ class DatabaseUserManager implements UserManagerDAO {
                     ":newEmail" => $newEmail,
                     ":vorname" => $vorname,
                     ":nachname" => $nachname,
-                    ":password" => password_hash(
-                        $password,
-                        PASSWORD_DEFAULT
-                    ),
+                    ":password" => password_hash($password, PASSWORD_DEFAULT),
                     ":oldEmail" => $oldEmail
                 ];
-
             } else {
-
                 $sql = "
                     UPDATE users
-                    SET
-                        email = :newEmail,
+                    SET email = :newEmail,
                         vorname = :vorname,
                         nachname = :nachname
                     WHERE email = :oldEmail
@@ -218,19 +147,16 @@ class DatabaseUserManager implements UserManagerDAO {
             }
 
             $command = $db->prepare($sql);
-
-            if (!$command) {
-                throw new RuntimeException(
-                    "Benutzer konnte nicht aktualisiert werden."
-                );
-            }
-
             $command->execute($params);
 
             return $command->rowCount() > 0;
 
         } catch (PDOException $e) {
-            throw new RuntimeException($e->getMessage());
+            if ($e->getCode() === "23000") {
+                throw new InvalidArgumentException("Diese E-Mail-Adresse wird bereits verwendet.");
+            }
+
+            throw new RuntimeException("Benutzer konnte nicht aktualisiert werden.");
         }
     }
 
@@ -240,15 +166,8 @@ class DatabaseUserManager implements UserManagerDAO {
             $db = $this->getConnection();
 
             $sql = "DELETE FROM users WHERE email = :email";
-
             $command = $db->prepare($sql);
 
-            if (!$command) {
-                throw new RuntimeException(
-                    "Benutzer konnte nicht gelöscht werden."
-                );
-            }
-
             $command->execute([
                 ":email" => $email
             ]);
@@ -256,8 +175,7 @@ class DatabaseUserManager implements UserManagerDAO {
             return $command->rowCount() > 0;
 
         } catch (PDOException $e) {
-            throw new RuntimeException($e->getMessage());
+            throw new RuntimeException("Benutzer konnte nicht gelöscht werden.");
         }
     }
-
 }
\ No newline at end of file