01: /*
02: /* $Id: NullIfFunction.java,v 1.5 2005/12/20 18:32:28 ahimanikya Exp $ tag
03: * =======================================================================
04: * Copyright (c) 2002-2005 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.Selectable;
48: import org.axiondb.types.AnyType;
49:
50: /**
51: * The NULLIF function returns a null value if the arguments are equal, otherwise it
52: * returns the value of the first argument.
53: * <p>
54: * The result of using NULLIF(e1,e2) is the same as using the expression
55: * <code>CASE WHEN e1=e2 THEN NULL ELSE e1 END</code>
56: *
57: * @version $Revision: 1.5 $ $Date: 2005/12/20 18:32:28 $
58: * @author Ahimanikya Satapathy
59: */
60: public class NullIfFunction extends BaseFunction implements
61: ScalarFunction, FunctionFactory {
62: public NullIfFunction() {
63: super ("NULLIF");
64: }
65:
66: public ConcreteFunction makeNewInstance() {
67: return new NullIfFunction();
68: }
69:
70: /** {@link AnyType} */
71: public DataType getDataType() {
72: return _returnType;
73: }
74:
75: public Object evaluate(RowDecorator row) throws AxionException {
76: Selectable sel1 = getArgument(0);
77: EqualFunction fn = new EqualFunction();
78: fn.addArgument(sel1);
79: fn.addArgument(getArgument(1));
80:
81: Boolean result = (Boolean) fn.evaluate(row);
82: if (result == null || !result.booleanValue()) {
83: // Must evaluate row with sel1 before getting datatype of sel1.
84: Object val = sel1.evaluate(row);
85: _returnType = sel1.getDataType();
86: return val;
87: }
88: return null;
89: }
90:
91: public boolean isValid() {
92: return (getArgumentCount() == 2);
93: }
94:
95: private DataType _returnType = AnyType.INSTANCE;
96: }
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