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;
14 import org.simantics.db.Session;
15 import org.simantics.db.WriteGraph;
16 import org.simantics.db.exception.CancelTransactionException;
17 import org.simantics.db.exception.DatabaseException;
20 * The <code>GraphRequest</code> interface is used to create transaction
21 * requests to Simantics database implementations. Both read and write
22 * transaction requests use the same interface.
25 * The actual work carried out by the implemented request should be done in the
26 * <code>perform</code> method. It receives a <code>Graph</code> instance as
27 * the only argument which is the interface for actually reading and writing the
31 * Transaction requests can be made to the database by creating your own
32 * <code>GraphRequest</code> instance and putting it in the request queue of
33 * the database session through the {@link Session} interface. The database
34 * session is responsible for executing the queued requests in a thread of its
35 * choice, or possibly/preferably multiple threads. The database session can
36 * allow multiple read-only requests to occur simultaneously, but read-write
37 * requests require exclusive database access. In other words only one
38 * read-write request can be in execution simultaneously.
41 * This interface also has two callbacks - <code>handleException</code> for
42 * allowing handling any exceptions thrown by <code>perform</code> and
43 * <code>requestCompleted</code> for performing actions after a request has
44 * been successfully completed.
47 * Clients of this interface are encouraged to extend the provided abstract
48 * implementations or this class or extend their own helper implementations for
49 * ones particular needs. The provided abstract implementations are:
51 * <li>{@link ReadGraphRequestAdapter} provides default implementations for
52 * everything except {@link #perform(WriteGraph)}.</li>
53 * <li>{@link SimpleGraphRequest} replaces {@link #perform(WriteGraph)} with
54 * {@link SimpleGraphRequest#run(WriteGraph)} for easier request implementation in
56 * <li>{@link GraphRequestWithResult} makes it easier for the user to return
57 * a single result Object from the request.</li>
60 * @author Tuukka Lehtonen
61 * @see ReadGraphRequestAdapter
62 * @see GraphRequestRunner
63 * @see GraphRequestStatus
64 * @see GraphRequestWithResult
66 * @see SimpleGraphRequest
68 public interface WriteResult<T> extends WriteTraits {
71 * When a <code>GraphRequest</code> is serviced by the database session
72 * the method <code>perform</code> is invoked.
75 * Perform receives an object instance implementing the <code>Graph</code>
76 * interface which provides the only way to read/write the graph data model.
77 * The Graph instance must only be valid during the execution of the
78 * <code>perform</code> method and therefore should not be stored for use
79 * outside of its execution.
82 * The general contract of the method <code>perform</code> is that it may
83 * take any action whatsoever which involves reading or writing the data
84 * model through the received Graph instance.
86 * @param g an interface for reading and writing the data model
87 * @return the result status of the request which affects how the
88 * transaction proceeds, see GraphRequestStatus for more information
89 * @throws Exception when anything goes wrong inside the request thread
90 * @throws CancelTransactionException to indicate that the request needs to
91 * be cancelled and any changes rolled back
93 T perform(WriteGraph graph) throws DatabaseException;