Add Reference/Collections

src/main/kotlin/nl/astraeus/persistence/reference/Reference.kt

@@ -0,0 +1,28 @@
+package nl.astraeus.nl.astraeus.persistence.reference
+
+import nl.astraeus.nl.astraeus.persistence.Persistable
+import nl.astraeus.nl.astraeus.persistence.currentTransaction
+import kotlin.reflect.KProperty
+
+class Reference<S : Persistable>(
+  val cls: Class<S>,
+  val setter: (Long?) -> Unit,
+  val getter: () -> Long?,
+) {
+
+  operator fun getValue(thisRef: Persistable, property: KProperty<*>): S? {
+    return currentTransaction()?.find(cls.kotlin, (getter() ?: 0L))
+  }
+
+  operator fun setValue(thisRef: Persistable, property: KProperty<*>, value: S?) {
+    if (value != null) {
+      // todo: only store if not already stored?
+      currentTransaction()?.store(value)
+    }
+    setter(value?.id)
+  }
+
+  companion object {
+    private const val serialVersionUID: Long = 1L
+  }
+}