1 /*******************************************************************************
2 * Copyright (c) 2007, 2010 Association for Decentralized Information Management
4 * All rights reserved. This program and the accompanying materials
5 * are made available under the terms of the Eclipse Public License v1.0
6 * which accompanies this distribution, and is available at
7 * http://www.eclipse.org/legal/epl-v10.html
10 * VTT Technical Research Centre of Finland - initial API and implementation
11 *******************************************************************************/
12 package org.simantics.db.request;
16 import org.simantics.db.ChangeSetIdentifier;
17 import org.simantics.db.Session;
18 import org.simantics.db.WriteGraph;
19 import org.simantics.db.exception.CancelTransactionException;
20 import org.simantics.db.exception.DatabaseException;
23 * The <code>GraphRequest</code> interface is used to create transaction
24 * requests to Simantics database implementations. Both read and write
25 * transaction requests use the same interface.
28 * The actual work carried out by the implemented request should be done in the
29 * <code>perform</code> method. It receives a <code>Graph</code> instance as
30 * the only argument which is the interface for actually reading and writing the
34 * Transaction requests can be made to the database by creating your own
35 * <code>GraphRequest</code> instance and putting it in the request queue of
36 * the database session through the {@link Session} interface. The database
37 * session is responsible for executing the queued requests in a thread of its
38 * choice, or possibly/preferably multiple threads. The database session can
39 * allow multiple read-only requests to occur simultaneously, but read-write
40 * requests require exclusive database access. In other words only one
41 * read-write request can be in execution simultaneously.
44 * This interface also has two callbacks - <code>handleException</code> for
45 * allowing handling any exceptions thrown by <code>perform</code> and
46 * <code>requestCompleted</code> for performing actions after a request has
47 * been successfully completed.
50 * Clients of this interface are encouraged to extend the provided abstract
51 * implementations or this class or extend their own helper implementations for
52 * ones particular needs. The provided abstract implementations are:
54 * <li>{@link ReadGraphRequestAdapter} provides default implementations for
55 * everything except {@link #perform(WriteGraph)}.</li>
56 * <li>{@link SimpleGraphRequest} replaces {@link #perform(WriteGraph)} with
57 * {@link SimpleGraphRequest#run(WriteGraph)} for easier request implementation in
59 * <li>{@link GraphRequestWithResult} makes it easier for the user to return
60 * a single result Object from the request.</li>
63 * @author Tuukka Lehtonen
64 * @see ReadGraphRequestAdapter
65 * @see GraphRequestRunner
66 * @see GraphRequestStatus
67 * @see GraphRequestWithResult
69 * @see SimpleGraphRequest
71 public interface DelayedWrite extends WriteTraits {
74 * When a <code>GraphRequest</code> is serviced by the database session
75 * the method <code>perform</code> is invoked.
78 * Perform receives an object instance implementing the <code>Graph</code>
79 * interface which provides the only way to read/write the graph data model.
80 * The Graph instance must only be valid during the execution of the
81 * <code>perform</code> method and therefore should not be stored for use
82 * outside of its execution.
85 * The general contract of the method <code>perform</code> is that it may
86 * take any action whatsoever which involves reading or writing the data
87 * model through the received Graph instance.
89 * @param g an interface for reading and writing the data model
90 * @return the result status of the request which affects how the
91 * transaction proceeds, see GraphRequestStatus for more information
92 * @throws Exception when anything goes wrong inside the request thread
93 * @throws CancelTransactionException to indicate that the request needs to
94 * be cancelled and any changes rolled back
96 void perform(WriteGraph graph) throws DatabaseException;
98 ChangeSetIdentifier getIdentifier();
100 void fillMetadata(Map<String, String> metadata);