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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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<div class="subTitle">com.sleepycat.persist.evolve</div>
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<h2 title="Interface Conversion" class="title">Interface Conversion</h2>
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<dt>All Superinterfaces:</dt>
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<dd>java.io.Serializable</dd>
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<br>
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<pre>public interface <span class="typeNameLabel">Conversion</span>
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extends java.io.Serializable</pre>
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<div class="block">Converts an old version of an object value to conform to the current class
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or field definition.
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<p>The <code>Conversion</code> interface is implemented by the user. A
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<code>Conversion</code> instance is passed to the <a href="../../../../com/sleepycat/persist/evolve/Converter.html#Converter-java.lang.String-int-java.lang.String-com.sleepycat.persist.evolve.Conversion-"><code>Converter.Converter(java.lang.String, int, java.lang.String, com.sleepycat.persist.evolve.Conversion)</code></a>
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constructor.</p>
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<p>The <code>Conversion</code> interface extends <code>Serializable</code> and the
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<code>Conversion</code> instance is serialized for storage using standard Java
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serialization. Normally, the <code>Conversion</code> class should only have
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transient fields that are initialized in the <a href="../../../../com/sleepycat/persist/evolve/Conversion.html#initialize-com.sleepycat.persist.model.EntityModel-"><code>initialize(com.sleepycat.persist.model.EntityModel)</code></a> method.
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While non-transient fields are allowed, care must be taken to only include
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fields that are serializable and will not pull in large amounts of data.</p>
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<p>When a class conversion is specified, two special considerations
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apply:</p>
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<ol>
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<li>A class conversion is only applied when to instances of that class. The
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conversion will not be applied when the class when it appears as a
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superclass of the instance's class. In this case, a conversion for the
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instance's class must also be specified.</li>
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<li>Although field renaming (as well as all other changes) is handled by the
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conversion method, a field Renamer is still needed when a secondary key
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field is renamed and field Deleter is still needed when a secondary key
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field is deleted. This is necessary for evolution of the metadata;
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specifically, if the key name changes the database must be renamed and if
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the key field is deleted the secondary database must be deleted.</li>
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</ol>
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<p>The <code>Conversion</code> class must implement the standard equals method.
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See <a href="../../../../com/sleepycat/persist/evolve/Conversion.html#equals-java.lang.Object-"><code>equals(java.lang.Object)</code></a> for more information.</p>
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<p>Conversions of simple types are generally simple. For example, a <code>String</code> field that contains only integer values can be easily converted to
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an <code>int</code> field:</p>
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<pre class="code">
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// The old class. Version 0 is implied.
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//
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@Persistent
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class Address {
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String zipCode;
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...
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}
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// The new class. A new version number must be assigned.
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//
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@Persistent(version=1)
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class Address {
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int zipCode;
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...
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}
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// The conversion class.
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//
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class MyConversion1 implements Conversion {
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public void initialize(EntityModel model) {
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// No initialization needed.
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}
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public Object convert(Object fromValue) {
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return Integer.valueOf((String) fromValue);
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}
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<code>@Override</code>
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public boolean equals(Object o) {
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return o instanceof MyConversion1;
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}
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}
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// Create a field converter mutation.
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//
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Converter converter = new Converter(Address.class.getName(), 0,
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"zipCode", new MyConversion1());
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// Configure the converter as described <a href="../../../../com/sleepycat/persist/evolve/Mutations.html" title="class in com.sleepycat.persist.evolve"><code>here</code></a>.</pre>
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<p>A conversion may perform arbitrary transformations on an object. For
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example, a conversion may transform a single String address field into an
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Address object containing four fields for street, city, state and zip
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code.</p>
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<pre class="code">
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// The old class. Version 0 is implied.
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//
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@Entity
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class Person {
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String address;
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...
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}
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// The new class. A new version number must be assigned.
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//
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@Entity(version=1)
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class Person {
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Address address;
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...
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}
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// The new address class.
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//
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@Persistent
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class Address {
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String street;
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String city;
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String state;
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int zipCode;
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...
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}
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class MyConversion2 implements Conversion {
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private transient RawType addressType;
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public void initialize(EntityModel model) {
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addressType = model.getRawType(Address.class.getName());
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}
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public Object convert(Object fromValue) {
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// Parse the old address and populate the new address fields
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//
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String oldAddress = (String) fromValue;
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Map<String, Object> addressValues = new HashMap<String, Object>();
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addressValues.put("street", parseStreet(oldAddress));
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addressValues.put("city", parseCity(oldAddress));
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addressValues.put("state", parseState(oldAddress));
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addressValues.put("zipCode", parseZipCode(oldAddress));
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// Return new raw Address object
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//
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return new RawObject(addressType, addressValues, null);
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}
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<code>@Override</code>
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public boolean equals(Object o) {
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return o instanceof MyConversion2;
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}
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private String parseStreet(String oldAddress) { ... }
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private String parseCity(String oldAddress) { ... }
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private String parseState(String oldAddress) { ... }
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private Integer parseZipCode(String oldAddress) { ... }
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}
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// Create a field converter mutation.
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//
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Converter converter = new Converter(Person.class.getName(), 0,
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"address", new MyConversion2());
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// Configure the converter as described <a href="../../../../com/sleepycat/persist/evolve/Mutations.html" title="class in com.sleepycat.persist.evolve"><code>here</code></a>.</pre>
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<p>Note that when a conversion returns a <a href="../../../../com/sleepycat/persist/raw/RawObject.html" title="class in com.sleepycat.persist.raw"><code>RawObject</code></a>, it must return
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it with a <a href="../../../../com/sleepycat/persist/raw/RawType.html" title="interface in com.sleepycat.persist.raw"><code>RawType</code></a> that is current as defined by the current class
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definitions. The proper types can be obtained from the <a href="../../../../com/sleepycat/persist/model/EntityModel.html" title="class in com.sleepycat.persist.model"><code>EntityModel</code></a>
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in the conversion's <a href="../../../../com/sleepycat/persist/evolve/Conversion.html#initialize-com.sleepycat.persist.model.EntityModel-"><code>initialize</code></a> method.</p>
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<p>A variation on the example above is where several fields in a class
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(street, city, state and zipCode) are converted to a single field (address).
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In this case a class converter rather than a field converter is used.</p>
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|
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<pre class="code">
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// The old class. Version 0 is implied.
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//
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@Entity
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class Person {
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String street;
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String city;
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String state;
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int zipCode;
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...
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}
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// The new class. A new version number must be assigned.
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//
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@Entity(version=1)
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class Person {
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Address address;
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...
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}
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// The new address class.
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//
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@Persistent
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class Address {
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String street;
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String city;
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String state;
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int zipCode;
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...
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}
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class MyConversion3 implements Conversion {
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private transient RawType newPersonType;
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private transient RawType addressType;
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public void initialize(EntityModel model) {
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newPersonType = model.getRawType(Person.class.getName());
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addressType = model.getRawType(Address.class.getName());
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}
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public Object convert(Object fromValue) {
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// Get field value maps for old and new objects.
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//
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RawObject person = (RawObject) fromValue;
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Map<String, Object> personValues = person.getValues();
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Map<String, Object> addressValues = new HashMap<String, Object>();
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RawObject address = new RawObject(addressType, addressValues, null);
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// Remove the old address fields and insert the new one.
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//
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addressValues.put("street", personValues.remove("street"));
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addressValues.put("city", personValues.remove("city"));
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addressValues.put("state", personValues.remove("state"));
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addressValues.put("zipCode", personValues.remove("zipCode"));
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personValues.put("address", address);
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return new RawObject(newPersonType, personValues, person.getSuper());
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}
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<code>@Override</code>
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public boolean equals(Object o) {
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return o instanceof MyConversion3;
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}
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}
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// Create a class converter mutation.
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//
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Converter converter = new Converter(Person.class.getName(), 0,
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new MyConversion3());
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// Configure the converter as described <a href="../../../../com/sleepycat/persist/evolve/Mutations.html" title="class in com.sleepycat.persist.evolve"><code>here</code></a>.</pre>
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|
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<p>A conversion can also handle changes to class hierarchies. For example,
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if a "name" field originally declared in class A is moved to its superclass
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B, a conversion can move the field value accordingly:</p>
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<pre class="code">
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// The old classes. Version 0 is implied.
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//
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@Persistent
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class A extends B {
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String name;
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...
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}
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@Persistent
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abstract class B {
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...
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}
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// The new classes. A new version number must be assigned.
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//
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@Persistent(version=1)
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class A extends B {
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...
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}
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@Persistent(version=1)
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abstract class B {
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String name;
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...
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}
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class MyConversion4 implements Conversion {
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private transient RawType newAType;
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private transient RawType newBType;
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public void initialize(EntityModel model) {
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newAType = model.getRawType(A.class.getName());
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newBType = model.getRawType(B.class.getName());
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}
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public Object convert(Object fromValue) {
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RawObject oldA = (RawObject) fromValue;
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RawObject oldB = oldA.getSuper();
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Map<String, Object> aValues = oldA.getValues();
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Map<String, Object> bValues = oldB.getValues();
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bValues.put("name", aValues.remove("name"));
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RawObject newB = new RawObject(newBType, bValues, oldB.getSuper());
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RawObject newA = new RawObject(newAType, aValues, newB);
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return newA;
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}
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<code>@Override</code>
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public boolean equals(Object o) {
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return o instanceof MyConversion4;
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}
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}
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// Create a class converter mutation.
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//
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Converter converter = new Converter(A.class.getName(), 0,
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new MyConversion4());
|
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|
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// Configure the converter as described <a href="../../../../com/sleepycat/persist/evolve/Mutations.html" title="class in com.sleepycat.persist.evolve"><code>here</code></a>.</pre>
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<p>A conversion may return an instance of a different class entirely, as
|
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long as it conforms to current class definitions and is the type expected
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in the given context (a subtype of the old type, or a type compatible with
|
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the new field type). For example, a field that is used to discriminate
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between two types of objects could be removed and replaced by two new
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subclasses:</p> <pre class="code">
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// The old class. Version 0 is implied.
|
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//
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@Persistent
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class Pet {
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boolean isCatNotDog;
|
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...
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}
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// The new classes. A new version number must be assigned to the Pet class.
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//
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@Persistent(version=1)
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class Pet {
|
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...
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}
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@Persistent
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class Cat extends Pet {
|
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...
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}
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@Persistent
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class Dog extends Pet {
|
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...
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}
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class MyConversion5 implements Conversion {
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private transient RawType newPetType;
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private transient RawType dogType;
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private transient RawType catType;
|
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public void initialize(EntityModel model) {
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newPetType = model.getRawType(Pet.class.getName());
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dogType = model.getRawType(Dog.class.getName());
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catType = model.getRawType(Cat.class.getName());
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}
|
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public Object convert(Object fromValue) {
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RawObject pet = (RawObject) fromValue;
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Map<String, Object> petValues = pet.getValues();
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Boolean isCat = (Boolean) petValues.remove("isCatNotDog");
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RawObject newPet = new RawObject(newPetType, petValues,
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pet.getSuper());
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RawType newSubType = isCat ? catType : dogType;
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return new RawObject(newSubType, Collections.emptyMap(), newPet);
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}
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<code>@Override</code>
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public boolean equals(Object o) {
|
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return o instanceof MyConversion5;
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}
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}
|
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|
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// Create a class converter mutation.
|
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//
|
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Converter converter = new Converter(Pet.class.getName(), 0,
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new MyConversion5());
|
|
|
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// Configure the converter as described <a href="../../../../com/sleepycat/persist/evolve/Mutations.html" title="class in com.sleepycat.persist.evolve"><code>here</code></a>.</pre>
|
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|
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<p>The primary limitation of a conversion is that it may access at most a
|
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single entity instance at one time. Conversions involving multiple entities
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at once may be made by performing a <a
|
|
href="package-summary.html#storeConversion">store conversion</a>.</p></div>
|
|
<dl>
|
|
<dt><span class="simpleTagLabel">Author:</span></dt>
|
|
<dd>Mark Hayes</dd>
|
|
<dt><span class="seeLabel">See Also:</span></dt>
|
|
<dd><a href="../../../../com/sleepycat/persist/evolve/package-summary.html"><code>Class Evolution</code></a></dd>
|
|
</dl>
|
|
</li>
|
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</ul>
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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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<!-- ========== METHOD SUMMARY =========== -->
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<ul class="blockList">
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<li class="blockList"><a name="method.summary">
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<!-- -->
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</a>
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<h3>Method Summary</h3>
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<table class="memberSummary" border="0" cellpadding="3" cellspacing="0" summary="Method Summary table, listing methods, and an explanation">
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<caption><span id="t0" class="activeTableTab"><span>All Methods</span><span class="tabEnd"> </span></span><span id="t2" class="tableTab"><span><a href="javascript:show(2);">Instance Methods</a></span><span class="tabEnd"> </span></span><span id="t3" class="tableTab"><span><a href="javascript:show(4);">Abstract Methods</a></span><span class="tabEnd"> </span></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">Method and Description</th>
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</tr>
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<tr id="i0" class="altColor">
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<td class="colFirst"><code>java.lang.Object</code></td>
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<td class="colLast"><code><span class="memberNameLink"><a href="../../../../com/sleepycat/persist/evolve/Conversion.html#convert-java.lang.Object-">convert</a></span>(java.lang.Object fromValue)</code>
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<div class="block">Converts an old version of an object value to conform to the current
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class or field definition.</div>
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</td>
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</tr>
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<tr id="i1" class="rowColor">
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<td class="colFirst"><code>boolean</code></td>
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<td class="colLast"><code><span class="memberNameLink"><a href="../../../../com/sleepycat/persist/evolve/Conversion.html#equals-java.lang.Object-">equals</a></span>(java.lang.Object other)</code>
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<div class="block">The standard <code>equals</code> method that must be implemented by
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conversion class.</div>
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</td>
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</tr>
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<tr id="i2" class="altColor">
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<td class="colFirst"><code>void</code></td>
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<td class="colLast"><code><span class="memberNameLink"><a href="../../../../com/sleepycat/persist/evolve/Conversion.html#initialize-com.sleepycat.persist.model.EntityModel-">initialize</a></span>(<a href="../../../../com/sleepycat/persist/model/EntityModel.html" title="class in com.sleepycat.persist.model">EntityModel</a> model)</code>
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<div class="block">Initializes the conversion, allowing it to obtain raw type information
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from the entity model.</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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</li>
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</ul>
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<div class="details">
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</a>
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<h3>Method Detail</h3>
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<a name="initialize-com.sleepycat.persist.model.EntityModel-">
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</a>
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<h4>initialize</h4>
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<pre>void initialize(<a href="../../../../com/sleepycat/persist/model/EntityModel.html" title="class in com.sleepycat.persist.model">EntityModel</a> model)</pre>
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<div class="block">Initializes the conversion, allowing it to obtain raw type information
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from the entity model.</div>
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<dl>
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<dt><span class="paramLabel">Parameters:</span></dt>
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<dd><code>model</code> - the EntityModel.</dd>
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</dl>
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</ul>
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<a name="convert-java.lang.Object-">
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<h4>convert</h4>
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<pre>java.lang.Object convert(java.lang.Object fromValue)</pre>
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<div class="block">Converts an old version of an object value to conform to the current
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class or field definition.
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<p>If a <code>RuntimeException</code> is thrown by this method, it will be
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thrown to the original caller. Similarly, a <code>IllegalArgumentException</code> will be thrown to the original caller if the
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object returned by this method does not conform to current class
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definitions.</p>
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<p>The class of the input and output object may be one of the simple
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types or <a href="../../../../com/sleepycat/persist/raw/RawObject.html" title="class in com.sleepycat.persist.raw"><code>RawObject</code></a>. For primitive types, the primitive wrapper
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class is used.</p></div>
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<dl>
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<dt><span class="paramLabel">Parameters:</span></dt>
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<dd><code>fromValue</code> - the object value being converted. The type of this
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value is defined by the old class version that is being converted.</dd>
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<dt><span class="returnLabel">Returns:</span></dt>
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<dd>the converted object. The type of this value must conform to
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a current class definition. If this is a class conversion, it must
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be the current version of the class. If this is a field conversion, it
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must be of a type compatible with the current declared type of the
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field.</dd>
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</dl>
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</li>
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</ul>
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<a name="equals-java.lang.Object-">
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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>equals</h4>
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<pre>boolean equals(java.lang.Object other)</pre>
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<div class="block">The standard <code>equals</code> method that must be implemented by
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conversion class.
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<p>When mutations are specified when opening a store, the specified and
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previously stored mutations are compared for equality. If they are
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equal, there is no need to replace the existing mutations in the stored
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catalog. To accurately determine equality, the conversion class must
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implement the <code>equals</code> method.</p>
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<p>If the <code>equals</code> method is not explicitly implemented by the
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conversion class or a superclass other than <code>Object</code>, <code>IllegalArgumentException</code> will be thrown when the store is opened.</p>
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<p>Normally whenever <code>equals</code> is implemented the <code>hashCode</code>
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method should also be implemented to support hash sets and maps.
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However, hash sets and maps containing <code>Conversion</code> objects
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are not used by the DPL and therefore the DPL does not require
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<code>hashCode</code> to be implemented.</p></div>
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<dl>
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<dt><span class="overrideSpecifyLabel">Overrides:</span></dt>
|
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<dd><code>equals</code> in class <code>java.lang.Object</code></dd>
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</dl>
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