diff -r fecda0f466e6 -r cf85ef18f231 src/main/java/de/uapcore/lightpit/AbstractLightPITServlet.java
--- a/src/main/java/de/uapcore/lightpit/AbstractLightPITServlet.java	Sun May 10 10:58:31 2020 +0200
+++ b/src/main/java/de/uapcore/lightpit/AbstractLightPITServlet.java	Mon May 11 19:09:06 2020 +0200
@@ -28,6 +28,8 @@
  */
 package de.uapcore.lightpit;
 
+import de.uapcore.lightpit.dao.DataAccessObjects;
+import de.uapcore.lightpit.dao.postgres.PGDataAccessObjects;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -39,6 +41,8 @@
 import java.io.IOException;
 import java.lang.reflect.Method;
 import java.lang.reflect.Modifier;
+import java.sql.Connection;
+import java.sql.SQLException;
 import java.util.*;
 
 /**
@@ -59,7 +63,7 @@
 
     @FunctionalInterface
     private interface HandlerMethod {
-        ResponseType apply(HttpServletRequest t, HttpServletResponse u) throws IOException;
+        ResponseType apply(HttpServletRequest request, HttpServletResponse response, DataAccessObjects dao) throws IOException, SQLException;
     }
 
     /**
@@ -82,21 +86,30 @@
         return (ModuleManager) getServletContext().getAttribute(ModuleManager.SC_ATTR_NAME);
     }
 
+
     /**
-     * Gives implementing modules access to the {@link DatabaseFacade}.
+     * Creates a set of data access objects for the specified connection.
      *
-     * @return the database facade
+     * @param connection the SQL connection
+     * @return a set of data access objects
      */
-    protected final DatabaseFacade getDatabaseFacade() {
-        return (DatabaseFacade) getServletContext().getAttribute(DatabaseFacade.SC_ATTR_NAME);
+    private DataAccessObjects createDataAccessObjects(Connection connection) throws SQLException {
+        final var df = (DatabaseFacade) getServletContext().getAttribute(DatabaseFacade.SC_ATTR_NAME);
+        switch (df.getSQLDialect()) {
+            case Postgres:
+                return new PGDataAccessObjects(connection);
+            default:
+                throw new AssertionError("Non-exhaustive switch - this is a bug.");
+        }
     }
 
-    private ResponseType invokeMapping(Method method, HttpServletRequest req, HttpServletResponse resp) throws IOException {
+    private ResponseType invokeMapping(Method method, HttpServletRequest req, HttpServletResponse resp, DataAccessObjects dao) throws IOException {
         try {
             LOG.trace("invoke {}#{}", method.getDeclaringClass().getName(), method.getName());
-            return (ResponseType) method.invoke(this, req, resp);
+            return (ResponseType) method.invoke(this, req, resp, dao);
         } catch (ReflectiveOperationException | ClassCastException ex) {
-            LOG.error(String.format("invocation of method %s failed", method.getName()), ex);
+            LOG.error("invocation of method {} failed: {}", method.getName(), ex.getMessage());
+            LOG.debug("Details: ", ex);
             resp.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
             return ResponseType.NONE;
         }
@@ -140,15 +153,16 @@
                     }
 
                     Class<?>[] params = method.getParameterTypes();
-                    if (params.length == 2
+                    if (params.length == 3
                             && HttpServletRequest.class.isAssignableFrom(params[0])
-                            && HttpServletResponse.class.isAssignableFrom(params[1])) {
+                            && HttpServletResponse.class.isAssignableFrom(params[1])
+                            && DataAccessObjects.class.isAssignableFrom(params[2])) {
 
                         final String requestPath = "/" + mapping.get().requestPath();
 
                         if (mappings.computeIfAbsent(mapping.get().method(), k -> new HashMap<>()).
                                 putIfAbsent(requestPath,
-                                        (req, resp) -> invokeMapping(method, req, resp)) != null) {
+                                        (req, resp, dao) -> invokeMapping(method, req, resp, dao)) != null) {
                             LOG.warn("{} {} has multiple mappings",
                                     mapping.get().method(),
                                     mapping.get().requestPath()
@@ -238,8 +252,7 @@
         }
     }
 
-    private void doProcess(HttpMethod method, HttpServletRequest req, HttpServletResponse resp)
-            throws ServletException, IOException {
+    private void doProcess(HttpMethod method, HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 
         // choose the requested language as session language (if available) or fall back to english, otherwise
         HttpSession session = req.getSession();
@@ -260,13 +273,21 @@
         req.setAttribute(Constants.REQ_ATTR_MODULE_CLASSNAME, this.getClass().getName());
         Optional.ofNullable(moduleInfo).ifPresent((proxy) -> req.setAttribute(Constants.REQ_ATTR_MODULE_INFO, proxy));
 
-
-        // call the handler, if available, or send an HTTP 404 error
-        Optional<HandlerMethod> mapping = findMapping(method, req);
-        if (mapping.isPresent()) {
-            forwardAsSpecified(mapping.get().apply(req, resp), req, resp);
-        } else {
-            resp.sendError(HttpServletResponse.SC_NOT_FOUND);
+        // obtain a connection and create the data access objects
+        final var db = (DatabaseFacade) req.getServletContext().getAttribute(DatabaseFacade.SC_ATTR_NAME);
+        try (final var connection = db.getDataSource().getConnection()) {
+            final var dao = createDataAccessObjects(connection);
+            // call the handler, if available, or send an HTTP 404 error
+            final var mapping = findMapping(method, req);
+            if (mapping.isPresent()) {
+                forwardAsSpecified(mapping.get().apply(req, resp, dao), req, resp);
+            } else {
+                resp.sendError(HttpServletResponse.SC_NOT_FOUND);
+            }
+        } catch (SQLException ex) {
+            LOG.error("Database exception (Code {}): {}", ex.getErrorCode(), ex.getMessage());
+            LOG.debug("Details: ", ex);
+            resp.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR, "Database Error - Code:" + ex.getErrorCode());
         }
     }