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