01: /*
02: * $Id: ExistsFunction.java,v 1.5 2005/03/01 22:58:42 ahimanikya Exp $
03: * =======================================================================
04: * Copyright (c) 2003-2005 Axion Development Team. All rights reserved.
05: *
06: * Redistribution and use in source and binary forms, with or without
07: * modification, are permitted provided that the following conditions
08: * are met:
09: *
10: * 1. Redistributions of source code must retain the above
11: * copyright notice, this list of conditions and the following
12: * disclaimer.
13: *
14: * 2. Redistributions in binary form must reproduce the above copyright
15: * notice, this list of conditions and the following disclaimer in
16: * the documentation and/or other materials provided with the
17: * distribution.
18: *
19: * 3. The names "Tigris", "Axion", nor the names of its contributors may
20: * not be used to endorse or promote products derived from this
21: * software without specific prior written permission.
22: *
23: * 4. Products derived from this software may not be called "Axion", nor
24: * may "Tigris" or "Axion" appear in their names without specific prior
25: * written permission.
26: *
27: * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
28: * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
29: * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
30: * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
31: * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
32: * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
33: * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
34: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
35: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
36: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
37: * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
38: * =======================================================================
39: */
40:
41: package org.axiondb.functions;
42:
43: import org.axiondb.AxionException;
44: import org.axiondb.DataType;
45: import org.axiondb.FunctionFactory;
46: import org.axiondb.RowDecorator;
47: import org.axiondb.RowIterator;
48: import org.axiondb.Selectable;
49: import org.axiondb.types.BooleanType;
50: import org.axiondb.engine.commands.SelectCommand;
51:
52: /**
53: * @version $Revision: 1.5 $ $Date: 2005/03/01 22:58:42 $
54: * @author Rahul Dwivedi
55: * @author Ahimanikya Satapathy
56: */
57: public class ExistsFunction extends BaseFunction implements
58: ScalarFunction, FunctionFactory {
59:
60: public ExistsFunction() {
61: super ("EXISTS");
62: }
63:
64: public ConcreteFunction makeNewInstance() {
65: return new ExistsFunction();
66: }
67:
68: public Object evaluate(RowDecorator row) throws AxionException {
69: Selectable sel = getArgument(0);
70:
71: if (sel instanceof SelectCommand) {
72: RowIterator iter = (RowIterator) sel.evaluate(row);
73: if (iter.hasNext()) {
74: return Boolean.TRUE;
75: }
76: return Boolean.FALSE;
77: }
78: return null;
79: }
80:
81: public DataType getDataType() {
82: return RETURN_TYPE;
83: }
84:
85: public boolean isValid() {
86: return (getArgumentCount() == 1);
87: }
88:
89: private static final DataType RETURN_TYPE = new BooleanType();
90: }
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