VersionValue


1   //$Id: VersionValue.java,v 1.1 2005/06/05 04:31:33 oneovthafew Exp $
2   package org.hibernate.engine;
3   
4   import org.apache.commons.logging.Log;
5   import org.apache.commons.logging.LogFactory;
6   import org.hibernate.MappingException;
7   import org.hibernate.id.IdentifierGeneratorFactory;
8   
9   /**
10   * A strategy for determining if a version value is an version of
11   * a new transient instance or a previously persistent transient instance.
12   * The strategy is determined by the <tt>unsaved-value</tt> attribute in
13   * the mapping file.
14   * 
15   * @author Gavin King
16   */
17  public class VersionValue {
18  
19      private static final Log log = LogFactory.getLog(VersionValue.class);
20  
21      private final Object   value;
22      /**
23       * Assume the transient instance is newly instantiated if the version
24       * is null, otherwise assume it is a detached instance.
25       */
26      public static final VersionValue NULL = new VersionValue() {
27          public final Boolean   isUnsaved(Object   version) {
28              log.trace("version unsaved-value strategy NULL");
29              return version==null ? Boolean.TRUE : Boolean.FALSE;
30          }
31          public Object   getDefaultValue(Object   currentValue) {
32              return null;
33          }
34          public String   toString() {
35              return "VERSION_SAVE_NULL";
36          }
37      };
38      /**
39       * Assume the transient instance is newly instantiated if the version
40       * is null, otherwise defer to the identifier unsaved-value.
41       */
42      public static final VersionValue UNDEFINED = new VersionValue() {
43          public final Boolean   isUnsaved(Object   version) {
44              log.trace("version unsaved-value strategy UNDEFINED");
45              return version==null ? Boolean.TRUE : null;
46          }
47          public Object   getDefaultValue(Object   currentValue) {
48              return currentValue;
49          }
50          public String   toString() {
51              return "VERSION_UNDEFINED";
52          }
53      };
54      /**
55       * Assume the transient instance is newly instantiated if the version
56       * is negative, otherwise assume it is a detached instance.
57       */
58      public static final VersionValue NEGATIVE = new VersionValue() {
59      
60          public final Boolean   isUnsaved(Object   version) throws MappingException {
61              log.trace("version unsaved-value strategy NEGATIVE");
62              if (version==null) return Boolean.TRUE;
63              if (version instanceof Number  ) {
64                  return ( (Number  ) version ).longValue() < 0l ? Boolean.TRUE : Boolean.FALSE;
65              }
66              else {
67                  throw new MappingException("unsaved-value NEGATIVE may only be used with short, int and long types");
68              }
69          }
70          public Object   getDefaultValue(Object   currentValue) {
71              return IdentifierGeneratorFactory.createNumber( -1l, currentValue.getClass() );
72          }
73          public String   toString() {
74              return "VERSION_NEGATIVE";
75          }
76      };
77      
78      protected VersionValue() {
79          this.value = null;
80      }
81  
82      /**
83       * Assume the transient instance is newly instantiated if
84       * its version is null or equal to <tt>value</tt>
85       * @param value value to compare to
86       */
87      public VersionValue(Object   value) {
88          this.value = value;
89      }
90      
91      /**
92       * Does the given version belong to a new instance?
93       *
94       * @param version version to check
95       * @return true is unsaved, false is saved, null is undefined
96       */
97      public Boolean   isUnsaved(Object   version) throws MappingException  {
98          if ( log.isTraceEnabled() ) log.trace("version unsaved-value: " + value);
99          return version==null || version.equals(value) ? Boolean.TRUE : Boolean.FALSE;
100     }
101     
102     public Object   getDefaultValue(Object   currentValue) {
103         return value;
104     }
105     
106     public String   toString() {
107         return "version unsaved-value: " + value;
108     }
109 }
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