01: /*
02: * Copyright (c) 1998-2008 Caucho Technology -- all rights reserved
03: *
04: * This file is part of Resin(R) Open Source
05: *
06: * Each copy or derived work must preserve the copyright notice and this
07: * notice unmodified.
08: *
09: * Resin Open Source is free software; you can redistribute it and/or modify
10: * it under the terms of the GNU General Public License as published by
11: * the Free Software Foundation; either version 2 of the License, or
12: * (at your option) any later version.
13: *
14: * Resin Open Source is distributed in the hope that it will be useful,
15: * but WITHOUT ANY WARRANTY; without even the implied warranty of
16: * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE, or any warranty
17: * of NON-INFRINGEMENT. See the GNU General Public License for more
18: * details.
19: *
20: * You should have received a copy of the GNU General Public License
21: * along with Resin Open Source; if not, write to the
22: * Free SoftwareFoundation, Inc.
23: * 59 Temple Place, Suite 330
24: * Boston, MA 02111-1307 USA
25: *
26: * @author Scott Ferguson
27: */
28:
29: package com.caucho.db.sql;
30:
31: import com.caucho.db.Database;
32: import com.caucho.db.store.Transaction;
33: import com.caucho.db.table.TableIterator;
34: import com.caucho.log.Log;
35: import com.caucho.sql.SQLExceptionWrapper;
36:
37: import java.io.IOException;
38: import java.sql.SQLException;
39: import java.util.logging.Logger;
40:
41: public class ExistsQuery extends SelectQuery {
42: private static final Logger log = Log.open(ExistsQuery.class);
43:
44: private static Expr[] _nullExprs = new Expr[0];
45:
46: protected ExistsQuery(Database db, String sql) throws SQLException {
47: super (db, sql);
48: }
49:
50: /**
51: * Executes the query.
52: */
53: public boolean exists(QueryContext context, Transaction xa)
54: throws SQLException {
55: SelectResult result = SelectResult.create(_nullExprs, null);
56:
57: try {
58: TableIterator[] rows = result.initRows(getFromItems());
59: context.init(xa, rows, isReadOnly());
60:
61: return execute(result, rows, context, xa);
62: } catch (IOException e) {
63: throw new SQLExceptionWrapper(e);
64: } finally {
65: context.unlock();
66:
67: result.close();
68: }
69: }
70:
71: /**
72: * Executes the query.
73: */
74: private boolean execute(SelectResult result, TableIterator[] rows,
75: QueryContext context, Transaction transaction)
76: throws SQLException, IOException {
77: FromItem[] fromItems = getFromItems();
78: int rowLength = fromItems.length;
79:
80: return start(rows, rowLength, context, transaction);
81: }
82:
83: /**
84: * Executes the query.
85: */
86: public void execute(QueryContext queryCtx, Transaction xa)
87: throws SQLException {
88: throw new UnsupportedOperationException();
89: }
90: }
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