org.camunda.bpm.engine.impl.migration.instance.MigratingProcessElementInstanceTopDownWalker Maven / Gradle / Ivy

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/*
 * Copyright Camunda Services GmbH and/or licensed to Camunda Services GmbH
 * under one or more contributor license agreements. See the NOTICE file
 * distributed with this work for additional information regarding copyright
 * ownership. Camunda licenses this file to you under the Apache License,
 * Version 2.0; 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.camunda.bpm.engine.impl.migration.instance;

import java.util.Collection;
import java.util.LinkedList;

import org.camunda.bpm.engine.impl.migration.instance.MigratingProcessElementInstanceTopDownWalker.MigrationContext;
import org.camunda.bpm.engine.impl.tree.ReferenceWalker;

/**
 * Walks the hierarchy of {@link MigratingProcessElementInstance}s in a top-down-fashion.
 * Maintains a context of the current instance and the {@link MigratingScopeInstanceBranch}
 * that it is in.
 *
 * @author Thorben Lindhauer
 */
public class MigratingProcessElementInstanceTopDownWalker extends ReferenceWalker {

  public MigratingProcessElementInstanceTopDownWalker(MigratingActivityInstance activityInstance) {
    super(new MigrationContext(activityInstance, new MigratingScopeInstanceBranch()));
  }

  @Override
  protected Collection nextElements() {

    Collection nextElements = new LinkedList();

    MigrationContext currentElement = getCurrentElement();

    // continue migration for non-leaf instances (i.e. scopes)
    if (currentElement.processElementInstance instanceof MigratingScopeInstance) {
      // Child instances share the same scope instance branch;
      // This ensures "once-per-parent" instantiation semantics,
      // i.e. if a new parent scope is added to more than one child, all those children
      // will share the same new parent instance.
      // By changing the way how the branches are created here, it should be possible
      // to implement other strategies, e.g. "once-per-child" semantics
      MigratingScopeInstanceBranch childrenScopeBranch = currentElement.scopeInstanceBranch.copy();
      MigratingScopeInstanceBranch childrenCompensationScopeBranch = currentElement.scopeInstanceBranch.copy();

      MigratingScopeInstance scopeInstance = (MigratingScopeInstance) currentElement.processElementInstance;

      childrenScopeBranch.visited(scopeInstance);
      childrenCompensationScopeBranch.visited(scopeInstance);

      for (MigratingProcessElementInstance child : scopeInstance.getChildren()) {
        MigratingScopeInstanceBranch instanceBranch = null;

        // compensation and non-compensation scopes cannot share the same scope instance branch
        // e.g. when adding a sub process, we want to create a new activity instance as well
        // as a new event scope instance for that sub process
        if (child instanceof MigratingEventScopeInstance
          || child instanceof MigratingCompensationEventSubscriptionInstance) {
          instanceBranch = childrenCompensationScopeBranch;
        }
        else {
          instanceBranch = childrenScopeBranch;
        }
        nextElements.add(new MigrationContext(
            child,
            instanceBranch));
      }
    }

    return nextElements;
  }

  public static class MigrationContext {
    protected MigratingProcessElementInstance processElementInstance;
    protected MigratingScopeInstanceBranch scopeInstanceBranch;

    public MigrationContext(MigratingProcessElementInstance processElementInstance, MigratingScopeInstanceBranch scopeInstanceBranch) {
      this.processElementInstance = processElementInstance;
      this.scopeInstanceBranch = scopeInstanceBranch;
    }

    public MigratingProcessElementInstance getProcessElementInstance() {
      return processElementInstance;
    }

    public MigratingScopeInstanceBranch getScopeInstanceBranch() {
      return scopeInstanceBranch;
    }
  }

}