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.services.xactn;
  
  import java.util.Optional;
  
  /**
   * Provides utilities to access active transactions associated with the
   * current thread.
   *
   * <p>
   *     This is a low-level service that domain objects will typically have
   *     little need to leverage; there will normally be a transaction started
   *     already by the framework at the beginning of an
   *     {@link org.apache.causeway.applib.services.iactn.Interaction} and committed
   *     at the end. On occasion though it can be useful to take
   *     explicit control over transaction boundaries, which is where the
   *     methods provided by this domain service can be useful.
   * </p>
   *
   * <p>
   *     NOTE: there is <i>no</i> method to close (which is to say to commit) an existing transaction, because of a
   *     subtlety with the JPA transaction manager: if a transaction wasn't a new one, then closing the transaction
   *     would actually mean to decrement the transaction counter (only when it hits zero should the transaction be
   *     committed); but if the previous transaction was instead suspended, the commit the new transaction and then
   *     resume the previous transaction.
   * </p>
   *
   * @since 2.0 {@index}
   */
  public interface TransactionService extends TransactionalProcessor {
  
      /**
       * Optionally returns the unique identifier of the current thread's transaction,
       * based on whether there is an active transaction associated with the current thread.
       */
      Optional<TransactionId> currentTransactionId();
  
      /**
       * Returns the state of the current thread's transaction., or returns
       * {@link TransactionState#NONE}, if there is no active transaction associated with the
       * current thread.
       */
      TransactionState currentTransactionState();
  
      /**
       * Flushes all changes to the object store.
       * <p>
       * Occasionally useful to ensure that newly persisted domain objects
       * are flushed to the database prior to a subsequent repository query.
       * <p>
       * If there is no active transaction associated with the current thread, then does nothing.
       */
      void flushTransaction();
  
  }
  