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18          <th colspan="3" align="center">Persistent Objects</th>
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32            <h2 class="title" style="clear: both"><a id="persistobject"></a>Persistent Objects</h2>
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36      <p>
37                  When using the DPL, you store data in the underlying
38                  DB databases by making objects
39                  <span class="emphasis"><em>persistent</em></span>. You do this using Java
40                  annotations that both identify the type of persistent
41                  object you are declaring, as well as the primary and
42                  secondary indices.
43          </p>
44      <p>
45                  The following are the annotations you will use with your
46                  DPL persistent classes:
47          </p>
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50          <colgroup>
51            <col />
52            <col />
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54          <thead>
55            <tr>
56              <th>Annotation</th>
57              <th>Description</th>
58            </tr>
59          </thead>
60          <tbody>
61            <tr>
62              <td>@Entity</td>
63              <td>
64                                    Declares an entity class; that is, a class with a primary index
65                                    and optionally one or more indices.
66                            </td>
67            </tr>
68            <tr>
69              <td>@Persistent</td>
70              <td>
71                                    Declares a persistent class; that is, a class used by an entity
72                                    class. They do not have indices but instead are are stored or
73                                    retrieved when an entity class makes direct use of them.
74                            </td>
75            </tr>
76            <tr>
77              <td>@PrimaryKey</td>
78              <td>
79                                    Declares a specific data member in an entity class to be the
80                                    primary key for that object. This annotation must be used one
81                                    and only one time for every entity class.
82                            </td>
83            </tr>
84            <tr>
85              <td>@SecondaryKey</td>
86              <td>
87                                    Declares a specific data member in an entity class to be a
88                                    secondary key for that object. This annotation is optional, and
89                                    can be used multiple times for an entity class.
90                            </td>
91            </tr>
92          </tbody>
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94      </div>
95      <p>
96                For example, the following is declared to be an entity class:
97        </p>
98      <pre class="programlisting">package persist.gettingStarted;
99
100import com.sleepycat.persist.model.Entity;
101import com.sleepycat.persist.model.PrimaryKey;
102
103@Entity
104public class ExampleEntity {
105
106    // The primary key must be unique in the database.
107    @PrimaryKey
108    private String aPrimaryKey;
109
110    @SecondaryKey(relate=MANY_TO_ONE)
111    private String aSecondaryKey;
112
113    ...
114
115    // The remainder of the class' implementation is purposefully
116    // omitted in the interest of brevity.
117
118    ...
119} </pre>
120      <p>
121            We discuss primary and secondary keys in more detail in <a class="xref" href="persist_index.html" title="Chapter��4.��Working with Indices">Working with Indices</a>.
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