Change.java

package com.gentics.mesh.changelog;

import com.tinkerpop.blueprints.TransactionalGraph;

/**
 * Interface for a mesh graph database change. A change may alter graph structure, content and indices.
 */
public interface Change {

	/**
	 * Return the uuid of the change.
	 * 
	 * @return
	 */
	String getUuid();

	/**
	 * Return the name of the change.
	 * 
	 * @return
	 */
	String getName();

	/**
	 * Apply the change to the graph.
	 */
	void apply();

	/**
	 * Check whether the change already has been applied.
	 * 
	 * @return
	 */
	boolean isApplied();

	/**
	 * Return the description of the change.
	 * 
	 * @return
	 */
	String getDescription();

	/**
	 * Set the graph instance to be used when handling the change.
	 * 
	 * @param graph
	 */
	void setGraph(TransactionalGraph graph);

	/**
	 * Return the graph that is currently set for the change.
	 * 
	 * @return
	 */
	TransactionalGraph getGraph();

	/**
	 * Persist the info that the change has been applied to the graph.
	 */
	void markAsComplete();

	/**
	 * Set the time that passed to execute the change.
	 * 
	 * @param timeMs
	 */
	void setDuration(long timeMs);

	/**
	 * Return the time it took to execute the change.
	 * 
	 * @return
	 */
	long getDuration();

	/**
	 * Validate the change. A unsuccessful validation will abort the changelog execution.
	 * 
	 * @return true if validation was successful. Otherwise false.
	 */
	boolean validate();

}

Change_093BEFB47FA4476FBE37FD27C613F7AA.java

/**
 * Example changelog entry.
 */
public class Change_093BEFB47FA4476FBE37FD27C613F7AA extends AbstractChange {

	@Override
	public String getName() {
		return "Add magic";
	}

	@Override
	public String getDescription() {
		return "Adds a magic vertex";
	}

	@Override
	public void apply() {
		Vertex meshRootVertex = getMeshRootVertex();
		Vertex newMagicVertex = getGraph().addVertex("magic");
		newMagicVertex.setProperty("name", "tinkerpop magic");
		meshRootVertex.addEdge("HAS_MAGIC", newMagicVertex);
		log.info("Added magic vertex");
	}

}

ChangelogExecutor.java

/**
 * Apply all listed changes.
 *
 * @param list
 * @return Flag which indicates whether all changes were applied successfully
 */
public boolean applyChanges(List<Change> list) {
	for (Change change : list) {
		// Execute each change in a new transaction
		TransactionalGraph graph = db.rawTx();
		change.setGraph(graph);
		try {
			if (!change.isApplied()) {
				log.info("Handling change {" + change.getUuid() + "}");
				log.info("Name: " + change.getName());
				log.info("Description: " + change.getDescription());

				long start = System.currentTimeMillis();
				change.apply();
				change.setDuration(System.currentTimeMillis() - start);
				if (!change.validate()) {
					throw new Exception("Validation for change {" + change.getUuid() + "/" + change.getName() + "} failed.");
				}
				change.markAsComplete();
			} else {
				log.debug("Change {" + change.getUuid() + "} is already applied.");
			}
		} catch (Exception e) {
			log.error("Error while handling change {" + change.getUuid() + "/" + change.getName() + "}. Invoking rollback..", e);
			graph.rollback();
			return false;
		} finally {
			graph.shutdown();
		}
	}
	return true;
}

ChangesList.java

/**
 * Typical list of changelog entries.
 */
public final class ChangesList {

	public static List<Change> getList() {
		List<Change> list = new ArrayList<>();
		list.add(new Change_093BEFB47FA4476FBE37FD27C613F7AA());
		return list;
	}
}