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377 lines
15 KiB
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<!-- Generated by javadoc (1.8.0_151) on Tue Oct 31 17:36:47 EDT 2017 -->
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<title>PrimaryKey (Oracle - Berkeley DB Java Edition API)</title>
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<div class="aboutLanguage"><b>Berkeley DB Java Edition</b><br><font size=\"-1\"> version 7.5.11</font>
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<li><a href="../../../../com/sleepycat/persist/model/PrimaryKeyMetadata.html" title="class in com.sleepycat.persist.model"><span class="typeNameLink">Next Class</span></a></li>
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<li>Summary: </li>
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<li>Field | </li>
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<li>Required | </li>
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<li><a href="#annotation.type.optional.element.summary">Optional</a></li>
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<li>Detail: </li>
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<li>Field | </li>
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<li><a href="#annotation.type.element.detail">Element</a></li>
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<!-- ======== START OF CLASS DATA ======== -->
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<div class="header">
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<div class="subTitle">com.sleepycat.persist.model</div>
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<h2 title="Annotation Type PrimaryKey" class="title">Annotation Type PrimaryKey</h2>
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</div>
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<div class="contentContainer">
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<div class="description">
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<hr>
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<br>
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<pre>@Documented
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@Retention(value=RUNTIME)
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@Target(value=FIELD)
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public @interface <span class="memberNameLabel">PrimaryKey</span></pre>
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<div class="block">Indicates the primary key field of an entity class. The value of the
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primary key field is the unique identifier for the entity in a <a href="../../../../com/sleepycat/persist/PrimaryIndex.html" title="class in com.sleepycat.persist"><code>PrimaryIndex</code></a>.
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<p><a href="../../../../com/sleepycat/persist/model/PrimaryKey.html" title="annotation in com.sleepycat.persist.model"><code>PrimaryKey</code></a> may appear on at most one declared field per
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class.</p>
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<p>Primary key values may be automatically assigned as sequential integers
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using a <a href="../../../../com/sleepycat/persist/model/PrimaryKey.html#sequence--"><code>sequence()</code></a>. In this case the type of the key field is
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restricted to a simple integer type.</p>
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<p>A primary key field may not be null, unless it is being assigned from a
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sequence.</p>
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<p><a name="keyTypes"><strong>Key Field Types</strong></a></p>
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<p>The type of a key field must either be one of the following:</p>
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<ul>
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<li>Any of the <a href="Entity.html#simpleTypes">simple types</a>.</li>
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<li>An enum type.</li>
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<li>A composite key class containing one or more simple type or enum
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fields.</li>
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</ul>
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<p>Array types are not allowed.</p>
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<p>When using a composite key class, each field of the composite key class
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must be annotated with <a href="../../../../com/sleepycat/persist/model/KeyField.html" title="annotation in com.sleepycat.persist.model"><code>KeyField</code></a> to identify the storage order and
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default sort order. See <a href="../../../../com/sleepycat/persist/model/KeyField.html" title="annotation in com.sleepycat.persist.model"><code>KeyField</code></a> for an example and more
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information on composite keys.</p>
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<p><a name="sortOrder"><strong>Key Sort Order</strong></a></p>
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<p>Key field types, being simple types, have a well defined and reasonable
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default sort order, described below. This sort order is based on a storage
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encoding that allows a fast byte-by-byte comparison.</p>
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<ul>
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<li>All simple types except for <code>String</code> are encoded so that they are
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sorted as expected, that is, as if the <code>Comparable.compareTo(T)</code> method
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of their class (or, for primitives, their wrapper class) is called.</li>
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<li>Strings are encoded as UTF-8 byte arrays. Zero (0x0000) character
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values are UTF encoded as non-zero values, and therefore embedded zeros in
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the string are supported. The sequence {0xC0,0x80} is used to
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encode a zero character. This UTF encoding is the same one used by native
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Java UTF libraries. However, this encoding of zero does impact the
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lexicographical ordering, and zeros will not be sorted first (the natural
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order) or last. For all character values other than zero, the default UTF
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byte ordering is the same as the Unicode lexicographical character
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ordering.</li>
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</ul>
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<p>When using a composite key class with more than one field, the sorting
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order among fields is determined by the <a href="../../../../com/sleepycat/persist/model/KeyField.html" title="annotation in com.sleepycat.persist.model"><code>KeyField</code></a> annotations. To
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override the default sort order, you can use a composite key class that
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implements <code>Comparable</code>. This allows overriding the sort order and is
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therefore useful even when there is only one key field in the composite key
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class. See <a href="KeyField.html#comparable">Custom Sort Order</a>
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for more information on sorting of composite keys.</p>
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<p><a name="inherit"><strong>Inherited Primary Key</strong></a></p>
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<p>If it does not appear on a declared field in the entity class, <code>PrimaryKey</code> must appear on a field of an entity superclass. In the
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following example, the primary key on the base class is used:</p>
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<pre class="code">
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@Persistent
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class BaseClass {
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@PrimaryKey
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long id;
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...
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}
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@Entity
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class Employee extends BaseClass {
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// inherits id primary key
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...
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}</pre>
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<p>If more than one class with <code>PrimaryKey</code> is present in a class
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hierarchy, the key in the most derived class is used. In this case, primary
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key fields in superclasses are "shadowed" and are not persistent. In the
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following example, the primary key in the base class is not used and is not
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persistent:</p>
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<pre class="code">
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@Persistent
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class BaseClass {
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@PrimaryKey
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long id;
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...
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}
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@Entity
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class Employee extends BaseClass {
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// overrides id primary key
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@PrimaryKey
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String uuid;
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...
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}</pre>
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<p>Note that a <code>PrimaryKey</code> is not allowed on entity subclasses. The
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following is illegal and will cause an <code>IllegalArgumentException</code> when
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trying to store an <code>Employee</code> instance:</p>
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<pre class="code">
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@Entity
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class Person {
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@PrimaryKey
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long id;
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...
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}
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@Persistent
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class Employee extends Person {
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@PrimaryKey
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String uuid;
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...
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}</pre></div>
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<dl>
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<dt><span class="simpleTagLabel">Author:</span></dt>
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<dd>Mark Hayes</dd>
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</dl>
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</li>
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</ul>
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||
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</div>
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<div class="summary">
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<ul class="blockList">
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<li class="blockList">
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<!-- =========== ANNOTATION TYPE OPTIONAL MEMBER SUMMARY =========== -->
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<ul class="blockList">
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<li class="blockList"><a name="annotation.type.optional.element.summary">
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<!-- -->
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</a>
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<h3>Optional Element Summary</h3>
|
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<table class="memberSummary" border="0" cellpadding="3" cellspacing="0" summary="Optional Element Summary table, listing optional elements, and an explanation">
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<caption><span>Optional Elements</span><span class="tabEnd"> </span></caption>
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<tr>
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<th class="colFirst" scope="col">Modifier and Type</th>
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<th class="colLast" scope="col">Optional Element and Description</th>
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</tr>
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<tr class="altColor">
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<td class="colFirst"><code>java.lang.String</code></td>
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<td class="colLast"><code><span class="memberNameLink"><a href="../../../../com/sleepycat/persist/model/PrimaryKey.html#sequence--">sequence</a></span></code>
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<div class="block">The name of a sequence from which to assign primary key values
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automatically.</div>
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</td>
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</tr>
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</table>
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</li>
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</ul>
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</li>
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</ul>
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</div>
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<div class="details">
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<ul class="blockList">
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<li class="blockList">
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<!-- ============ ANNOTATION TYPE MEMBER DETAIL =========== -->
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<ul class="blockList">
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<li class="blockList"><a name="annotation.type.element.detail">
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<!-- -->
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</a>
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<h3>Element Detail</h3>
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<a name="sequence--">
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<!-- -->
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</a>
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<ul class="blockListLast">
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<li class="blockList">
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<h4>sequence</h4>
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<pre>public abstract java.lang.String sequence</pre>
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<div class="block">The name of a sequence from which to assign primary key values
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automatically. If a non-empty string is specified, sequential integers
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will be assigned from the named sequence.
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<p>A single sequence may be used for more than one entity class by
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specifying the same sequence name for each <code>PrimaryKey</code>. For
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each named sequence, a <a href="../../../../com/sleepycat/je/Sequence.html" title="class in com.sleepycat.je"><code>Sequence</code></a> will be used to
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|
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assign key values. For more information on configuring sequences, see
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|
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<a href="../../../../com/sleepycat/persist/EntityStore.html#setSequenceConfig-java.lang.String-com.sleepycat.je.SequenceConfig-"><code>EntityStore.setSequenceConfig</code></a>.</p>
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|
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<p>To use a sequence, the type of the key field must be a primitive
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integer type (<code>byte</code>, <code>short</code>, <code>int</code> or <code>long</code>)
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or the primitive wrapper class for one of these types. A composite key
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class may also be used to override sort order, but it may contain only a
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single key field, and this field must have one of the types previously
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mentioned.</p>
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|
|
|
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<p>When an entity with a primary key sequence is stored using one of the
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<code>put</code> methods in the <a href="../../../../com/sleepycat/persist/PrimaryIndex.html" title="class in com.sleepycat.persist"><code>PrimaryIndex</code></a>, a new key will be
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assigned if the primary key field in the entity instance is null (for a
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reference type) or zero (for a primitive integer type). Specifying zero
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for a primitive integer key field is allowed because the initial value
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of the sequence is one (not zero) by default. If the sequence
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configuration is changed such that zero is part of the sequence, then
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the field type must be a primitive wrapper class and the field value
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must be null to cause a new key to be assigned.</p>
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<p>When one of the <code>put</code> methods in the <a href="../../../../com/sleepycat/persist/PrimaryIndex.html" title="class in com.sleepycat.persist"><code>PrimaryIndex</code></a>
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is called and a new key is assigned, the assigned value is returned to
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the caller via the key field of the entity object that is passed as a
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parameter.</p></div>
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<dl>
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<dt><span class="returnLabel">Returns:</span></dt>
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<dd>the sequence name or an empty string.</dd>
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</dl>
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<dl>
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<dt>Default:</dt>
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<dd>""</dd>
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</dl>
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</li>
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</ul>
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||
|
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</li>
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|
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</ul>
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|
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</li>
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|
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</ul>
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|
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</div>
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|
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</div>
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|
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<!-- ========= END OF CLASS DATA ========= -->
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</a>
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<div class="skipNav"><a href="#skip.navbar.bottom" title="Skip navigation links">Skip navigation links</a></div>
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</a>
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<ul class="navList" title="Navigation">
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<li><a href="../../../../overview-summary.html">Overview</a></li>
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<li><a href="package-summary.html">Package</a></li>
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<li class="navBarCell1Rev">Class</li>
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<li><a href="class-use/PrimaryKey.html">Use</a></li>
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<li><a href="../../../../deprecated-list.html">Deprecated</a></li>
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