diff -r 4f912cd42876 -r 86b5d8a1662f src/main/kotlin/de/uapcore/lightpit/dao/AbstractDao.kt
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/main/kotlin/de/uapcore/lightpit/dao/AbstractDao.kt	Thu Nov 19 13:58:54 2020 +0100
@@ -0,0 +1,65 @@
+/*
+ * Copyright 2020 Mike Becker. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+package de.uapcore.lightpit.dao
+
+import java.sql.PreparedStatement
+import java.sql.ResultSet
+import java.sql.Types
+
+abstract class AbstractDao<T> {
+
+    abstract fun mapResult(rs: ResultSet): T
+
+    protected fun list(stmt: PreparedStatement): List<T> {
+        return sequence {
+            stmt.executeQuery().use { result ->
+                while (result.next()) yield(mapResult(result))
+            }
+        }.toList()
+    }
+
+    protected fun find(stmt: PreparedStatement): T? {
+        stmt.executeQuery().use { result ->
+            return if (result.next()) {
+                mapResult(result)
+            } else {
+                null
+            }
+        }
+    }
+
+    // TODO: create PreparedStatement abstraction that provides some features
+
+    // TODO: remove the following legacy code helper function
+    protected fun <T> setForeignKeyOrNull(stmt: PreparedStatement, index: Int, instance: T?, keyGetter: (obj: T) -> Int) {
+        if (instance == null) {
+            stmt.setNull(index, Types.INTEGER)
+        } else {
+            stmt.setInt(index, keyGetter(instance))
+        }
+    }
+}
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