ExpressionBuilder


1   package org.enhydra.shark.api.common;
2   
3   /**
4    * ExpressionBuilder interface helps building expressions for any
5    * BaseIterator implementation.
6    * 
7    * Expirience has learned us that it's not that easy to build any
8    * usefull expression to be used in xxIterators. Since Shark supports
9    * BeanShell and JavaScript, making expressions starts to be even more
10   * complicated once you start to use string literals. Also, reading
11   * and debugging of such expression might turn into very tedious task.
12   * On the other side OMG (or at least the way we read it) explicitely
13   * says set_expression method takes String as parameter, and there's
14   * no escape.
15   * ExpressionBuilder and it's extending interfaces/classes serves the
16   * intention to ease this task, although there is another benefit - 
17   * it allows us to prepare such expressions xxIterator can execute
18   * directly against database, thus improving the performance.
19   * 
20   * @author Vladimir Puskas
21   * @version 0.2
22   */
23  public interface ExpressionBuilder {
24     
25     public static final boolean ORDER_ASCENDING = true;
26     public static final boolean ORDER_DESCENDING = false;
27     
28     /**
29      * Comment for <code>AND_OPERATOR</code>
30      */
31     public static final int AND_OPERATOR = 1;
32  
33     /**
34      * Comment for <code>OR_OPERATOR</code>
35      */
36     public static final int OR_OPERATOR = 2;
37  
38     /**
39      * Comment for <code>NOT_OPERATOR</code>
40      */
41     public static final int NOT_OPERATOR = 4;
42  
43     /**
44      * @return true if expression can be performed on DB entirely
45      */
46     public boolean isComplete();
47  
48     /**
49      * @return sql interpretation of expression prepared to fit into
50      *         WHERE clause
51      */
52     public String   toSQL();
53  
54     /**
55      * @return expression in target script language
56      */
57     public String   toScript();
58     
59     /**
60      * @return expression that should be set to appropriate iterator.
61      */
62     public String   toExpression();
63     
64  }
65
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