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