content: /*
   *  Licensed to the Apache Software Foundation (ASF) under one
   *  or more contributor license agreements.  See the NOTICE file
   *  distributed with this work for additional information
   *  regarding copyright ownership.  The ASF licenses this file
   *  to you under the Apache License, Version 2.0 (the
   *  "License"); you may not use this file except in compliance
   *  with the License.  You may obtain a copy of the License at
   *
   *        http://www.apache.org/licenses/LICENSE-2.0
   *
   *  Unless required by applicable law or agreed to in writing,
   *  software distributed under the License is distributed on an
   *  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
   *  KIND, either express or implied.  See the License for the
   *  specific language governing permissions and limitations
   *  under the License.
   */
  package org.apache.causeway.applib.annotation;
  
  import java.lang.annotation.ElementType;
  import java.lang.annotation.Inherited;
  import java.lang.annotation.Retention;
  import java.lang.annotation.RetentionPolicy;
  import java.lang.annotation.Target;
  
  import org.apache.causeway.applib.events.domain.CollectionDomainEvent;
  
  /**
   * Domain semantics for domain object collection.
   *
   * @see Action
   * @see Property
   * @see DomainObject
   * @see CollectionLayout
   *
   * @since 1.x {@index}
   */
  @Inherited
  @Target({
          ElementType.METHOD,
          ElementType.FIELD,
          ElementType.RECORD_COMPONENT,
          ElementType.TYPE,
          ElementType.ANNOTATION_TYPE})
  @Retention(RetentionPolicy.RUNTIME)
  @DomainObject(nature=Nature.MIXIN, mixinMethod = "coll") // meta annotation, only applies at class level
  @Domain.Include // meta annotation, in support of meta-model validation
  public @interface Collection {
  
      /**
       * Indicates that changes to the collection that should be posted to the
       * {@link org.apache.causeway.applib.services.eventbus.EventBusService event bus} using a custom (subclass of)
       * {@link org.apache.causeway.applib.events.domain.CollectionDomainEvent}.
       *
       * <p>
       *     Subscribers of this event can interact with the business rule
       *     checking (hide, disable, validate) and its modification (before and
       *     after).
       * </p>
       *
       * <p>For example:
       * </p>
       * <pre>
       * public class Order {
       *   public static class OrderLineItems extends CollectionDomainEvent { ... }
       *
       *   &#64;CollectionInteraction(OrderLineItems.class)
       *   public SortedSet&lt;OrderLine&gt; getLineItems() { ...}
       * }
       * </pre>
       *
       * <p>
       * This subclass must provide a no-arg constructor; the fields are set reflectively.
       * </p>
       *
       * @see Action#domainEvent()
       * @see Property#domainEvent()
       * @see DomainObject#collectionDomainEvent()
       */
      Class<? extends CollectionDomainEvent<?,?>> domainEvent()
              default CollectionDomainEvent.Default.class;
  
      /**
       * The type-of the elements held within the collection.
       *
       * <p>
       *     This is only provided as a fallback; usually the framework can infer
       *     the element type of the collection from the collection method's
       *     generic type.
       * </p>
       *
       * @see Action#typeOf()
       */
      Class<?> typeOf()
              default void.class; // represents unspecified
  
  }
  