diff --git a/bean/src/main/java/io/github/mmm/entity/property/link/LinkProperty.java b/bean/src/main/java/io/github/mmm/entity/property/link/LinkProperty.java
index e0a9898..1f1a042 100644
--- a/bean/src/main/java/io/github/mmm/entity/property/link/LinkProperty.java
+++ b/bean/src/main/java/io/github/mmm/entity/property/link/LinkProperty.java
@@ -1,293 +1,340 @@
-/* Copyright (c) The m-m-m Team, Licensed under the Apache License, Version 2.0
- * http://www.apache.org/licenses/LICENSE-2.0 */
-package io.github.mmm.entity.property.link;
-
-import java.util.function.Function;
-
-import io.github.mmm.entity.Entity;
-import io.github.mmm.entity.bean.EntityBean;
-import io.github.mmm.entity.id.Id;
-import io.github.mmm.entity.id.IdMarshalling;
-import io.github.mmm.entity.link.IdLink;
-import io.github.mmm.entity.link.Link;
-import io.github.mmm.entity.link.LinkMapper;
-import io.github.mmm.entity.property.id.IdProperty;
-import io.github.mmm.marshall.StructuredReader;
-import io.github.mmm.marshall.StructuredWriter;
-import io.github.mmm.property.PropertyMetadata;
-import io.github.mmm.property.ReadableProperty;
-import io.github.mmm.property.criteria.CriteriaPredicate;
-import io.github.mmm.property.criteria.PredicateOperator;
-import io.github.mmm.property.object.ObjectProperty;
-import io.github.mmm.value.PropertyPath;
-import io.github.mmm.value.ReadableValue;
-import io.github.mmm.value.converter.TypeMapper;
-
-/**
- * {@link ObjectProperty} with {@link Link} {@link #getValue() value} {@link Link#getTarget() pointing to} an
- * {@link io.github.mmm.entity.bean.EntityBean entity}.
- *
- * @param <E> the generic type of the {@link Link#getTarget() linked} {@link io.github.mmm.entity.bean.EntityBean
- *        entity}.
- *
- * @since 1.0.0
- */
-public class LinkProperty<E extends EntityBean> extends ObjectProperty<Link<E>> {
-
-  private Class<E> entityClass;
-
-  private Function<Id<E>, E> resolver;
-
-  private LinkMapper typeMapper;
-
-  /**
-   * The constructor.
-   *
-   * @param name the {@link #getName() name}.
-   * @param entityClass the optional {@link Class} of the linked entity.
-   * @param metadata the {@link #getMetadata() metadata}.
-   */
-  public LinkProperty(String name, Class<E> entityClass, PropertyMetadata<Link<E>> metadata) {
-
-    this(name, entityClass, metadata, null);
-  }
-
-  /**
-   * The constructor.
-   *
-   * @param name the {@link #getName() name}.
-   * @param entityClass the optional {@link Class} of the linked entity.
-   * @param metadata the {@link #getMetadata() metadata}.
-   * @param resolver the optional {@link IdLink#of(Id, Function) resolver function}.
-   */
-  @SuppressWarnings({ "rawtypes", "unchecked" })
-  public LinkProperty(String name, Class<E> entityClass, PropertyMetadata<Link<E>> metadata,
-      Function<Id<E>, E> resolver) {
-
-    super(name, (Class) Link.class, metadata);
-    this.entityClass = entityClass;
-    this.resolver = resolver;
-  }
-
-  /**
-   * The constructor.
-   *
-   * @param name the {@link #getName() name}.
-   * @param value the (initial) {@link #get() value}.
-   * @param metadata the {@link #getMetadata() metadata}.
-   */
-  public LinkProperty(String name, Link<E> value, PropertyMetadata<Link<E>> metadata) {
-
-    this(name, value, metadata, null);
-  }
-
-  /**
-   * The constructor.
-   *
-   * @param name the {@link #getName() name}.
-   * @param value the (initial) {@link #get() value}.
-   * @param metadata the {@link #getMetadata() metadata}.
-   * @param resolver the optional {@link IdLink#of(Id, Function) resolver function}.
-   */
-  public LinkProperty(String name, Link<E> value, PropertyMetadata<Link<E>> metadata, Function<Id<E>, E> resolver) {
-
-    super(name, value, metadata);
-    this.entityClass = value.getId().getEntityClass();
-    this.resolver = resolver;
-  }
-
-  @Override
-  protected void doSet(Link<E> newValue) {
-
-    if (newValue != null) {
-      Id<E> id = newValue.getId();
-      if (id != null) {
-        if (this.entityClass == null) {
-          this.entityClass = id.getEntityClass();
-        } else {
-          Class<E> idEntityType = id.getEntityClass();
-          if (idEntityType == null) {
-            if (newValue instanceof IdLink) {
-              newValue = ((IdLink<E>) newValue).withType(this.entityClass);
-            }
-          } else if (!this.entityClass.isAssignableFrom(idEntityType)) {
-            throw new IllegalArgumentException("Cannot set link of type " + idEntityType.getName() + " to property "
-                + getName() + " with incompatible entity type " + this.entityClass.getName());
-          }
-        }
-      }
-    }
-    super.doSet(newValue);
-  }
-
-  /**
-   * @return the linked {@link EntityBean entity}.
-   * @see Link#getTarget()
-   */
-  public E getEntity() {
-
-    Link<E> link = get();
-    if (link == null) {
-      return null;
-    }
-    return link.getTarget();
-  }
-
-  /**
-   * @return the {@link Id#getEntityClass() entity class}.
-   */
-  @SuppressWarnings({ "unchecked", "rawtypes" })
-  public Class<E> getEntityClass() {
-
-    if (this.entityClass == null) {
-      Link<E> link = get();
-      if (link != null) {
-        Id<E> id = link.getId();
-        if (id != null) {
-          this.entityClass = id.getEntityClass();
-        } else if (link.isResolved()) {
-          E target = link.getTarget();
-          this.entityClass = (Class) ((EntityBean) target).getType().getJavaClass();
-        }
-      }
-    }
-    return this.entityClass;
-  }
-
-  @SuppressWarnings({ "unchecked", "rawtypes" })
-  @Override
-  public TypeMapper<Link<E>, Id<E>> getTypeMapper() {
-
-    if (this.typeMapper == null) {
-      this.typeMapper = new LinkMapper(this.resolver);
-    }
-    return (TypeMapper) this.typeMapper;
-  }
-
-  @Override
-  protected void readValue(StructuredReader reader) {
-
-    Id<E> id = IdMarshalling.get().readObject(reader, this.entityClass);
-    IdLink<E> link = IdLink.of(id, this.resolver);
-    setValue(link);
-  }
-
-  @Override
-  public void write(StructuredWriter writer) {
-
-    Id<E> id = null;
-    Link<E> link = getValue();
-    if (link != null) {
-      id = link.getId();
-    }
-    IdMarshalling.get().writeObject(writer, id);
-  }
-
-  /**
-   * @see #eq(Object)
-   * @param other the literal {@link Id} to compare with using {@link PredicateOperator#EQ = (equal)}.
-   * @return the resulting {@link CriteriaPredicate}.
-   */
-  public CriteriaPredicate eq(Id<E> other) {
-
-    return eq(Link.of(other));
-  }
-
-  /**
-   * @see #eq(Object)
-   * @param other the {@link IdProperty} to compare with using {@link PredicateOperator#EQ = (equal)}.
-   * @return the resulting {@link CriteriaPredicate}.
-   */
-  @SuppressWarnings({ "rawtypes", "unchecked" })
-  public CriteriaPredicate eq(IdProperty other) {
-
-    return predicate((ReadableProperty) this, PredicateOperator.EQ, (PropertyPath) other);
-  }
-
-  /**
-   * @see #eq(Object)
-   * @param other the literal {@link Entity} whose {@link Entity#getId() ID} to compare with using
-   *        {@link PredicateOperator#EQ = (equal)}.
-   * @return the resulting {@link CriteriaPredicate}.
-   */
-  public CriteriaPredicate eq(E other) {
-
-    if ((other != null) && (other.getId() == null)) {
-      return eq(other.Id());
-    }
-    return eq(Link.of(other));
-  }
-
-  /**
-   * @see #neq(Object)
-   * @param other the literal {@link Id} to compare with using {@link PredicateOperator#NEQ != (not-equal)}.
-   * @return the resulting {@link CriteriaPredicate}.
-   */
-  public CriteriaPredicate neq(Id<E> other) {
-
-    return neq(Link.of(other));
-  }
-
-  /**
-   * @see #neq(Object)
-   * @param other the literal {@link Entity} whose {@link Entity#getId() ID} to compare with using
-   *        {@link PredicateOperator#NEQ != (not-equal)}.
-   * @return the resulting {@link CriteriaPredicate}.
-   */
-  public CriteriaPredicate neq(E other) {
-
-    if ((other != null) && (other.getId() == null)) {
-      return neq(other.Id());
-    }
-    return neq(Link.of(other));
-  }
-
-  /**
-   * @see #neq(Object)
-   * @param other the {@link IdProperty} to compare with using {@link PredicateOperator#NEQ != (not-equal)}.
-   * @return the resulting {@link CriteriaPredicate}.
-   */
-  @SuppressWarnings({ "rawtypes", "unchecked" })
-  public CriteriaPredicate neq(IdProperty other) {
-
-    return predicate((ReadableProperty) this, PredicateOperator.NEQ, (PropertyPath) other);
-  }
-
-  private <V> CriteriaPredicate predicate(ReadableProperty<V> property1, PredicateOperator op,
-      PropertyPath<V> property2) {
-
-    return CriteriaPredicate.of(property1, op, property2);
-  }
-
-  /**
-   * <b>ATTENTION:<b><br>
-   * This is an internal method for framework code.
-   *
-   * @param resolver new resolver {@link Function}.
-   * @see IdLink#setResolver(Function)
-   */
-  @SuppressWarnings("unchecked")
-  public void setResolver(Function<Id<E>, E> resolver) {
-
-    // TODO: checks?
-    this.resolver = resolver;
-    this.typeMapper = null;
-    Link<E> link = doGet();
-    if ((link != null) && !link.isResolved()) {
-      if (link instanceof IdLink idLink) {
-        idLink.setResolver(resolver);
-      }
-    }
-  }
-
-  @Override
-  public void copyValue(ReadableValue<Link<E>> other) {
-
-    Link<E> link = other.get();
-    if ((link != null) && link.isResolved()) {
-      link = Link.of(link.getId());
-    }
-    set(link);
-  }
-
-}
+/* Copyright (c) The m-m-m Team, Licensed under the Apache License, Version 2.0
+ * http://www.apache.org/licenses/LICENSE-2.0 */
+package io.github.mmm.entity.property.link;
+
+import java.util.function.Function;
+import java.util.function.Supplier;
+
+import io.github.mmm.bean.WritableBean;
+import io.github.mmm.entity.Entity;
+import io.github.mmm.entity.bean.EntityBean;
+import io.github.mmm.entity.id.Id;
+import io.github.mmm.entity.id.IdMarshalling;
+import io.github.mmm.entity.link.AbstractLink;
+import io.github.mmm.entity.link.IdLink;
+import io.github.mmm.entity.link.Link;
+import io.github.mmm.entity.link.LinkMapper;
+import io.github.mmm.entity.property.id.IdProperty;
+import io.github.mmm.marshall.StructuredReader;
+import io.github.mmm.marshall.StructuredWriter;
+import io.github.mmm.property.PropertyMetadata;
+import io.github.mmm.property.ReadableProperty;
+import io.github.mmm.property.criteria.CriteriaPredicate;
+import io.github.mmm.property.criteria.PredicateOperator;
+import io.github.mmm.property.object.ObjectProperty;
+import io.github.mmm.value.PropertyPath;
+import io.github.mmm.value.ReadableValue;
+import io.github.mmm.value.converter.TypeMapper;
+
+/**
+ * {@link ObjectProperty} with {@link Link} {@link #getValue() value} {@link Link#getTarget() pointing to} an
+ * {@link io.github.mmm.entity.bean.EntityBean entity}.
+ *
+ * @param <E> the generic type of the {@link Link#getTarget() linked} {@link io.github.mmm.entity.bean.EntityBean
+ *        entity}.
+ *
+ * @since 1.0.0
+ */
+public class LinkProperty<E extends EntityBean> extends ObjectProperty<Link<E>> {
+
+  private Class<E> entityClass;
+
+  private Function<Id<E>, E> resolver;
+
+  private LinkMapper typeMapper;
+
+  /**
+   * The constructor.
+   *
+   * @param name the {@link #getName() name}.
+   * @param entityClass the optional {@link Class} of the linked entity.
+   * @param metadata the {@link #getMetadata() metadata}.
+   */
+  public LinkProperty(String name, Class<E> entityClass, PropertyMetadata<Link<E>> metadata) {
+
+    this(name, entityClass, metadata, null);
+  }
+
+  /**
+   * The constructor.
+   *
+   * @param name the {@link #getName() name}.
+   * @param entityClass the optional {@link Class} of the linked entity.
+   * @param metadata the {@link #getMetadata() metadata}.
+   * @param resolver the optional {@link IdLink#of(Id, Function) resolver function}.
+   */
+  @SuppressWarnings({ "rawtypes", "unchecked" })
+  public LinkProperty(String name, Class<E> entityClass, PropertyMetadata<Link<E>> metadata,
+      Function<Id<E>, E> resolver) {
+
+    super(name, (Class) Link.class, metadata);
+    this.entityClass = entityClass;
+    this.resolver = resolver;
+  }
+
+  /**
+   * The constructor.
+   *
+   * @param name the {@link #getName() name}.
+   * @param value the (initial) {@link #get() value}.
+   * @param metadata the {@link #getMetadata() metadata}.
+   */
+  public LinkProperty(String name, Link<E> value, PropertyMetadata<Link<E>> metadata) {
+
+    this(name, value, metadata, null);
+  }
+
+  /**
+   * The constructor.
+   *
+   * @param name the {@link #getName() name}.
+   * @param value the (initial) {@link #get() value}.
+   * @param metadata the {@link #getMetadata() metadata}.
+   * @param resolver the optional {@link IdLink#of(Id, Function) resolver function}.
+   */
+  public LinkProperty(String name, Link<E> value, PropertyMetadata<Link<E>> metadata, Function<Id<E>, E> resolver) {
+
+    super(name, value, metadata);
+    this.entityClass = value.getId().getEntityClass();
+    this.resolver = resolver;
+  }
+
+  @Override
+  protected void doSet(Link<E> newValue) {
+
+    if (newValue != null) {
+      Id<E> id = newValue.getId();
+      if (id != null) {
+        if (this.entityClass == null) {
+          this.entityClass = id.getEntityClass();
+        } else {
+          Class<E> idEntityType = id.getEntityClass();
+          if (idEntityType == null) {
+            if (newValue instanceof IdLink) {
+              newValue = ((IdLink<E>) newValue).withType(this.entityClass);
+            }
+          } else if (!this.entityClass.isAssignableFrom(idEntityType)) {
+            throw new IllegalArgumentException("Cannot set link of type " + idEntityType.getName() + " to property "
+                + getName() + " with incompatible entity type " + this.entityClass.getName());
+          }
+        }
+      }
+    }
+    super.doSet(newValue);
+  }
+
+  /**
+   * @return the linked {@link EntityBean entity}.
+   * @see Link#getTarget()
+   */
+  public E getEntity() {
+
+    Link<E> link = get();
+    if (link == null) {
+      return null;
+    }
+    return link.getTarget();
+  }
+
+  /**
+   * @return the {@link Id#getEntityClass() entity class}.
+   */
+  @SuppressWarnings({ "unchecked", "rawtypes" })
+  public Class<E> getEntityClass() {
+
+    if (this.entityClass == null) {
+      Link<E> link = get();
+      if (link != null) {
+        Id<E> id = link.getId();
+        if (id != null) {
+          this.entityClass = id.getEntityClass();
+        } else if (link.isResolved()) {
+          E target = link.getTarget();
+          this.entityClass = (Class) ((EntityBean) target).getType().getJavaClass();
+        }
+      }
+    }
+    return this.entityClass;
+  }
+
+  @SuppressWarnings({ "unchecked", "rawtypes" })
+  @Override
+  public TypeMapper<Link<E>, Id<E>> getTypeMapper() {
+
+    if (this.typeMapper == null) {
+      this.typeMapper = new LinkMapper(this.resolver);
+    }
+    return (TypeMapper) this.typeMapper;
+  }
+
+  @Override
+  public boolean isValueMutable() {
+
+    return true; // IdLink without resolver function is actually immutable but lets keep it simple
+  }
+
+  @Override
+  protected Supplier<? extends Link<E>> createReadOnlyExpression() {
+
+    final ReadOnlyLink readOnlyLink = new ReadOnlyLink();
+    return () -> {
+      Link<E> link = get();
+      if (link == null) {
+        return null;
+      }
+      return readOnlyLink;
+    };
+  }
+
+  @Override
+  protected void readValue(StructuredReader reader) {
+
+    Id<E> id = IdMarshalling.get().readObject(reader, this.entityClass);
+    IdLink<E> link = IdLink.of(id, this.resolver);
+    setValue(link);
+  }
+
+  @Override
+  public void write(StructuredWriter writer) {
+
+    Id<E> id = null;
+    Link<E> link = getValue();
+    if (link != null) {
+      id = link.getId();
+    }
+    IdMarshalling.get().writeObject(writer, id);
+  }
+
+  /**
+   * @see #eq(Object)
+   * @param other the literal {@link Id} to compare with using {@link PredicateOperator#EQ = (equal)}.
+   * @return the resulting {@link CriteriaPredicate}.
+   */
+  public CriteriaPredicate eq(Id<E> other) {
+
+    return eq(Link.of(other));
+  }
+
+  /**
+   * @see #eq(Object)
+   * @param other the {@link IdProperty} to compare with using {@link PredicateOperator#EQ = (equal)}.
+   * @return the resulting {@link CriteriaPredicate}.
+   */
+  @SuppressWarnings({ "rawtypes", "unchecked" })
+  public CriteriaPredicate eq(IdProperty other) {
+
+    return predicate((ReadableProperty) this, PredicateOperator.EQ, (PropertyPath) other);
+  }
+
+  /**
+   * @see #eq(Object)
+   * @param other the literal {@link Entity} whose {@link Entity#getId() ID} to compare with using
+   *        {@link PredicateOperator#EQ = (equal)}.
+   * @return the resulting {@link CriteriaPredicate}.
+   */
+  public CriteriaPredicate eq(E other) {
+
+    if ((other != null) && (other.getId() == null)) {
+      return eq(other.Id());
+    }
+    return eq(Link.of(other));
+  }
+
+  /**
+   * @see #neq(Object)
+   * @param other the literal {@link Id} to compare with using {@link PredicateOperator#NEQ != (not-equal)}.
+   * @return the resulting {@link CriteriaPredicate}.
+   */
+  public CriteriaPredicate neq(Id<E> other) {
+
+    return neq(Link.of(other));
+  }
+
+  /**
+   * @see #neq(Object)
+   * @param other the literal {@link Entity} whose {@link Entity#getId() ID} to compare with using
+   *        {@link PredicateOperator#NEQ != (not-equal)}.
+   * @return the resulting {@link CriteriaPredicate}.
+   */
+  public CriteriaPredicate neq(E other) {
+
+    if ((other != null) && (other.getId() == null)) {
+      return neq(other.Id());
+    }
+    return neq(Link.of(other));
+  }
+
+  /**
+   * @see #neq(Object)
+   * @param other the {@link IdProperty} to compare with using {@link PredicateOperator#NEQ != (not-equal)}.
+   * @return the resulting {@link CriteriaPredicate}.
+   */
+  @SuppressWarnings({ "rawtypes", "unchecked" })
+  public CriteriaPredicate neq(IdProperty other) {
+
+    return predicate((ReadableProperty) this, PredicateOperator.NEQ, (PropertyPath) other);
+  }
+
+  private <V> CriteriaPredicate predicate(ReadableProperty<V> property1, PredicateOperator op,
+      PropertyPath<V> property2) {
+
+    return CriteriaPredicate.of(property1, op, property2);
+  }
+
+  /**
+   * <b>ATTENTION:<b><br>
+   * This is an internal method for framework code.
+   *
+   * @param resolver new resolver {@link Function}.
+   * @see IdLink#setResolver(Function)
+   */
+  @SuppressWarnings("unchecked")
+  public void setResolver(Function<Id<E>, E> resolver) {
+
+    // TODO: checks?
+    this.resolver = resolver;
+    this.typeMapper = null;
+    Link<E> link = doGet();
+    if ((link != null) && !link.isResolved()) {
+      if (link instanceof IdLink idLink) {
+        idLink.setResolver(resolver);
+      }
+    }
+  }
+
+  @Override
+  public void copyValue(ReadableValue<Link<E>> other) {
+
+    Link<E> link = other.get();
+    if ((link != null) && link.isResolved()) {
+      link = Link.of(link.getId());
+    }
+    set(link);
+  }
+
+  private class ReadOnlyLink extends AbstractLink<E> {
+    @Override
+    public Id<E> getId() {
+
+      return get().getId();
+    }
+
+    @Override
+    public E getTarget() {
+
+      E target = get().getTarget();
+      if (target != null) {
+        target = WritableBean.getReadOnly(target);
+      }
+      return target;
+    }
+
+    @Override
+    public boolean isResolved() {
+
+      return get().isResolved();
+    }
+
+  }
+
+}
diff --git a/bean/src/test/java/io/github/mmm/entity/property/PropertyTest.java b/bean/src/test/java/io/github/mmm/entity/bean/PropertyTest.java
similarity index 96%
rename from bean/src/test/java/io/github/mmm/entity/property/PropertyTest.java
rename to bean/src/test/java/io/github/mmm/entity/bean/PropertyTest.java
index 5708d60..18b683c 100644
--- a/bean/src/test/java/io/github/mmm/entity/property/PropertyTest.java
+++ b/bean/src/test/java/io/github/mmm/entity/bean/PropertyTest.java
@@ -1,4 +1,4 @@
-package io.github.mmm.entity.property;
+package io.github.mmm.entity.bean;
 
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
diff --git a/bean/src/test/java/io/github/mmm/entity/property/link/LinkPropertyTest.java b/bean/src/test/java/io/github/mmm/entity/property/link/LinkPropertyTest.java
index 2ea5dbe..808eca1 100644
--- a/bean/src/test/java/io/github/mmm/entity/property/link/LinkPropertyTest.java
+++ b/bean/src/test/java/io/github/mmm/entity/property/link/LinkPropertyTest.java
@@ -1,12 +1,15 @@
 package io.github.mmm.entity.property.link;
 
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
 import org.junit.jupiter.api.Test;
 
+import io.github.mmm.base.exception.ReadOnlyException;
 import io.github.mmm.bean.BeanFactory;
+import io.github.mmm.entity.bean.PropertyTest;
 import io.github.mmm.entity.id.Id;
 import io.github.mmm.entity.id.LongVersionId;
 import io.github.mmm.entity.link.Link;
-import io.github.mmm.entity.property.PropertyTest;
 import io.github.mmm.property.WritableProperty;
 
 /**
@@ -46,9 +49,16 @@ public void testReadOnly() {
     assertThat((Object) readOnlyLinkProperty.get()).isNull();
     linkProperty.set(LINK);
     Link<Target> readOnlyLink = readOnlyLinkProperty.get();
-    readOnlyLink.getTarget().setId(id2);
-    // assertThat(readOnlyLink).isNotNull().isNotSameAs(LINK);
+    assertThrows(ReadOnlyException.class, () -> {
+      readOnlyLink.getTarget().setId(id2);
+    });
+    assertThat(readOnlyLink).isNotNull().isNotSameAs(LINK);
+  }
+
+  @Override
+  protected void verifyReadOnlyValue(LinkProperty<Target> readOnly) {
 
+    assertThat(readOnly.get()).isNotNull().isNotSameAs(LINK);
   }
 
 }