concept Entity > NamedConcept {

}

abstract concept AbstractJavaObjectEntity<A> > Entity {

  abstract A object();

  toString {

    S s = super.toString();

    O o = object();

    if (o != null)

      s += " " + str_pcall(o);

    ret s;

  }

}

concept TransientJavaObjectEntity<A> > AbstractJavaObjectEntity<A> {

  gettable transient A object;

}

concept PersistentJavaObjectEntity<A> > AbstractJavaObjectEntity<A> {

  gettable A object;

}

concept ConceptEntity<A extends Concept> extends AbstractJavaObjectEntity<A> {

  new Ref<A> concept;

  *(A concept) { this.concept.set(concept); }

  A object() { ret concept!; }

}

concept FieldInObjectEntity > Entity {

  new Ref<AbstractJavaObjectEntity<?>> objectEntity;

  S fieldName;

  *(AbstractJavaObjectEntity objectEntity, S *fieldName) {

    this.objectEntity.set(objectEntity);

  }

  O value() { ret !objectEntity.has() ? null : getOpt(objectEntity->object(), fieldName); }

  toString {

    S s = super.toString() + " " + fieldName + " in " + objectEntity;

    O value = value();

    if (value != null)

      s += appendBracketed("value of type " + className(value));

    ret s;

  }

}

concept DeclaredFieldEntity > Entity {

  Class theClass;

  S fieldName;

  *(Class *theClass, S *fieldName) {}

  Field fieldObject() { ret findFieldOfClass(theClass, fieldName); }

  toString {

    var fieldObject = fieldObject();

    ret super.toString() + " " + (fieldObject != null ? str(fieldObject)

      : "[field not found: " + className(theClass) + "." + fieldName + "]");

  }

}