diff --git a/src/main/kotlin/org/sirius/dorm/model/ObjectDescriptorBuilder.kt b/src/main/kotlin/org/sirius/dorm/model/ObjectDescriptorBuilder.kt
index 15091fb..8625a4e 100644
--- a/src/main/kotlin/org/sirius/dorm/model/ObjectDescriptorBuilder.kt
+++ b/src/main/kotlin/org/sirius/dorm/model/ObjectDescriptorBuilder.kt
@@ -122,12 +122,12 @@ class ObjectDescriptorBuilder(val manager: ObjectManager, val name: String) {
     private val properties = ArrayList<PropertyDescriptor<Any>>()
 
     init {
-        property(id)
+        define(id)
     }
 
     // fluent
 
-    fun property(propertyBuilder: PropertyBuilder) : ObjectDescriptorBuilder {
+    fun define(propertyBuilder: PropertyBuilder) : ObjectDescriptorBuilder {
         properties.add(propertyBuilder.build())
 
         return this
diff --git a/src/main/kotlin/org/sirius/dorm/object/Attribute.kt b/src/main/kotlin/org/sirius/dorm/object/Attribute.kt
index e5177de..a6b594d 100644
--- a/src/main/kotlin/org/sirius/dorm/object/Attribute.kt
+++ b/src/main/kotlin/org/sirius/dorm/object/Attribute.kt
@@ -1,6 +1,7 @@
 package org.sirius.dorm.`object`
 
 import org.sirius.dorm.ObjectManager
+import org.sirius.dorm.ObjectManagerError
 import org.sirius.dorm.model.PropertyDescriptor
 import org.sirius.dorm.persistence.entity.PropertyEntity
 
diff --git a/src/main/kotlin/org/sirius/dorm/object/MultiValuedRelation.kt b/src/main/kotlin/org/sirius/dorm/object/MultiValuedRelation.kt
index ed19a3b..d2faa40 100644
--- a/src/main/kotlin/org/sirius/dorm/object/MultiValuedRelation.kt
+++ b/src/main/kotlin/org/sirius/dorm/object/MultiValuedRelation.kt
@@ -73,6 +73,8 @@ class MultiValuedRelation(relation: RelationDescriptor<*>, status: Status, val o
 
     override fun flush() {
         if (isLoaded()) {
+            val n = if (relation.isOwner() ) "targets" else "sources"
+
             // synchronize the objects set with the property.relations
 
             val targetMap = HashMap<Long, PropertyEntity>()
@@ -88,8 +90,12 @@ class MultiValuedRelation(relation: RelationDescriptor<*>, status: Status, val o
             for (target in objects!!) {
                 val key = target.id
 
-                if (!targetMap.containsKey(key))
-                    relations.add(target.values[relation.index].property!!)
+                if (!targetMap.containsKey(key)) {
+                    val property = target.values[relation.inverseRelation!!.index].property!!
+
+                    println("add ${property.entity.id}.${property.attribute} to entity[${obj.id}].${relation.name}.${n}")
+                    relations.add(property)
+                }
                 else
                     targetMap.remove(key)
             } // for
@@ -97,6 +103,7 @@ class MultiValuedRelation(relation: RelationDescriptor<*>, status: Status, val o
             // deleted
 
             for (deleted in targetMap.values) {
+                println("delete ${deleted.entity.id}.${property!!.attribute} from entity[${obj.id}].${relation.name}.${n}")
                 relations.remove(deleted)
             } // if
         }
diff --git a/src/main/kotlin/org/sirius/dorm/object/Property.kt b/src/main/kotlin/org/sirius/dorm/object/Property.kt
index 0f4828b..efeb2f6 100644
--- a/src/main/kotlin/org/sirius/dorm/object/Property.kt
+++ b/src/main/kotlin/org/sirius/dorm/object/Property.kt
@@ -29,5 +29,7 @@ abstract class Property(var property: PropertyEntity?) {
         return false
     }
 
+    open fun validate() {}
+
     open fun flush() {}
 }
\ No newline at end of file
diff --git a/src/main/kotlin/org/sirius/dorm/object/SingleValuedRelation.kt b/src/main/kotlin/org/sirius/dorm/object/SingleValuedRelation.kt
index 4675113..6bd6d92 100644
--- a/src/main/kotlin/org/sirius/dorm/object/SingleValuedRelation.kt
+++ b/src/main/kotlin/org/sirius/dorm/object/SingleValuedRelation.kt
@@ -51,15 +51,50 @@ class SingleValuedRelation(relation: RelationDescriptor<*>, status: Status, val
 
     // override
 
+    override fun validate() {
+        if ( target === null &&  !relation.multiplicity.optional)
+            throw ObjectManagerError("relation ${obj.type.name}.${relation.name} is required")
+    }
+
     override fun flush() {
         if ( isLoaded()) {
-            relations().clear()
-            if ( target !== null) {
-                relations().add(target!!.values[relation.inverseRelation!!.index].property!!)
+            // validate
+
+            validate()
+
+            // adjust relation
+
+            val relationenEntities = relations()
+
+            val n = if (relation.isOwner() ) "targets" else "sources"
+
+            if ( target === null) {
+                if ( relationenEntities.isNotEmpty()) {
+                    if ( relationenEntities.size > 1)
+                        throw Error("iuch")
+
+                    val property = relationenEntities.first()
+
+                    relationenEntities.clear()
+
+                    println("remove ${property.entity.id}.${property.attribute} from entity[${obj.id}].${relation.name}.${n}")
+                }
             }
             else {
-                if ( !relation.multiplicity.optional)
-                    throw ObjectManagerError("relation ${obj.type.name}.${relation.name} is required")
+                if ( relationenEntities.size == 1) {
+                    val property = relationenEntities.first()
+                    if (property.entity !== target!!.entity ) {
+                        println("add ${property.entity.id}.${property.attribute} to entity[${obj.id}].${relation.name}.${n}")
+                        relationenEntities.add(property)
+                    }
+                }
+
+                if (relationenEntities.size == 0) {
+                    val property = target!!.values[relation.inverseRelation!!.index].property!!
+                    println("add ${property.entity.id}.${property.attribute} to entity[${obj.id}].${relation.name}.${n}")
+                    relationenEntities.add(property)
+                }
+                else  throw Error("iuch")
             }
         }
     }
diff --git a/src/main/kotlin/org/sirius/dorm/persistence/entity/PropertyEntity.kt b/src/main/kotlin/org/sirius/dorm/persistence/entity/PropertyEntity.kt
index 76c088d..9596c9d 100644
--- a/src/main/kotlin/org/sirius/dorm/persistence/entity/PropertyEntity.kt
+++ b/src/main/kotlin/org/sirius/dorm/persistence/entity/PropertyEntity.kt
@@ -43,7 +43,7 @@ data class PropertyEntity(
     @Column(name = "DOUBLE_VALUE")
     var doubleValue : Double,
 
-    @ManyToMany(fetch = FetchType.LAZY, cascade = [CascadeType.REMOVE])
+    @ManyToMany(fetch = FetchType.LAZY)
     @JoinTable(
         name = "RELATIONS",
         joinColumns = [JoinColumn(name = "FROM_ATTR"), JoinColumn(name = "FROM_ENTITY")],
@@ -51,7 +51,13 @@ data class PropertyEntity(
     )
     val targets : MutableSet<PropertyEntity> = HashSet(),
 
-    @ManyToMany(mappedBy="targets", fetch = FetchType.LAZY)
+    //@ManyToMany(mappedBy="targets", fetch = FetchType.LAZY)
+    @ManyToMany(fetch = FetchType.LAZY)
+    @JoinTable(
+        name = "RELATIONS",
+        joinColumns = [JoinColumn(name = "TO_ATTR"), JoinColumn(name = "TO_ENTITY")],
+        inverseJoinColumns = [JoinColumn(name = "FROM_ATTR"), JoinColumn(name = "FROM_ENTITY")]
+    )
     val sources : MutableSet<PropertyEntity> = HashSet(),
 ) {
     // override Object