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1   /*
2    * #%L
3    * NaryExpression.java - mongodb-async-driver - Allanbank Consulting, Inc.
4    * %%
5    * Copyright (C) 2011 - 2014 Allanbank Consulting, Inc.
6    * %%
7    * Licensed under the Apache License, Version 2.0 (the "License");
8    * you may not use this file except in compliance with the License.
9    * You may obtain a copy of the License at
10   * 
11   *      http://www.apache.org/licenses/LICENSE-2.0
12   * 
13   * Unless required by applicable law or agreed to in writing, software
14   * distributed under the License is distributed on an "AS IS" BASIS,
15   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16   * See the License for the specific language governing permissions and
17   * limitations under the License.
18   * #L%
19   */
20  package com.allanbank.mongodb.builder.expression;
21  
22  import java.io.StringWriter;
23  import java.util.ArrayList;
24  import java.util.List;
25  
26  import com.allanbank.mongodb.bson.Element;
27  import com.allanbank.mongodb.bson.ElementAssignable;
28  import com.allanbank.mongodb.bson.element.ArrayElement;
29  import com.allanbank.mongodb.bson.element.DocumentElement;
30  import com.allanbank.mongodb.bson.element.JsonSerializationVisitor;
31  
32  /**
33   * NaryExpression provides an implementation of an {@link Expression} with 2-N
34   * operands.
35   * 
36   * @api.no This class is <b>NOT</b> part of the drivers API. This class may be
37   *         mutated in incompatible ways between any two releases of the driver.
38   * @copyright 2012-2013, Allanbank Consulting, Inc., All Rights Reserved
39   */
40  public class NaryExpression implements Expression, ElementAssignable {
41  
42      /** The expression expressed as an {@link ArrayElement}. */
43      protected final ArrayElement myExpressions;
44  
45      /**
46       * Creates a new NaryExpression.
47       * 
48       * @param operator
49       *            The operator this object represents.
50       * @param expressions
51       *            The sub expressions.
52       */
53      public NaryExpression(final String operator,
54              final Expression... expressions) {
55          final List<Element> elements = new ArrayList<Element>(
56                  expressions.length);
57          for (int i = 0; i < expressions.length; ++i) {
58              elements.add(expressions[i].toElement(String.valueOf(i)));
59          }
60  
61          myExpressions = new ArrayElement(operator, elements);
62      }
63  
64      /**
65       * {@inheritDoc}
66       * <p>
67       * Overridden to return the sub expressions as a {@link ArrayElement}:
68       * </p>
69       * <blockquote>
70       * 
71       * <pre>
72       * <code>
73       * "$op" : [ &lt;e1&gt;, &lt;e2&gt;, &lt;e2&gt;, ... ]
74       * </code>
75       * </pre>
76       * 
77       * </blockquote>
78       */
79      @Override
80      public ArrayElement asElement() {
81          return myExpressions;
82      }
83  
84      /**
85       * {@inheritDoc}
86       * <p>
87       * Overridden to return the sub expressions as a document with a nested
88       * array element:
89       * </p>
90       * <blockquote>
91       * 
92       * <pre>
93       * <code>
94       * { &lt;name&gt; : { "$op" : [ &lt;e1&gt;, &lt;e2&gt;, &lt;e2&gt;, ... ] } }
95       * </code>
96       * </pre>
97       * 
98       * </blockquote>
99       */
100     @Override
101     public DocumentElement toElement(final String name) {
102         return new DocumentElement(name, myExpressions);
103     }
104 
105     /**
106      * {@inheritDoc}
107      * <p>
108      * Overridden to return the expression in JSON format.
109      * </p>
110      * <blockquote>
111      * 
112      * <pre>
113      * <code>
114      * "$op" : [ &lt;e1&gt;, &lt;e2&gt;, &lt;e2&gt;, ... ]
115      * </code>
116      * </pre>
117      * 
118      * </blockquote>
119      */
120     @Override
121     public String toString() {
122         final StringWriter sink = new StringWriter();
123         final JsonSerializationVisitor json = new JsonSerializationVisitor(
124                 sink, true);
125 
126         myExpressions.accept(json);
127 
128         return sink.toString();
129     }
130 }