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<title>Berkeley DB: Db.set_dup_compare</title>
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<h1>Db.set_dup_compare</h1>
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import com.sleepycat.db.*;
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public interface DbDupCompare
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public abstract int dup_compare(Db db, Dbt dbt1, Dbt dbt2);
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public void set_dup_compare(DbDupCompare dup_compare)
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<p>Set the duplicate data item comparison function. The comparison function
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is called when it is necessary to compare a data item specified by the
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application with a data item currently stored in the tree. The first
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argument to the comparison function is the <a href="../api_java/dbt_class.html">Dbt</a> representing the
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application's data item; the second is the current tree's data item.
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Calling Db.set_dup_compare implies calling <a href="../api_java/db_set_flags.html">Db.set_flags</a>
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with the <a href="../api_java/db_set_flags.html#DB_DUPSORT">Db.DB_DUPSORT</a> flag.
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<p>The comparison function must return an integer value less than, equal
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to, or greater than zero if the first data item argument is considered
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to be respectively less than, equal to, or greater than the second data
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item argument. In addition, the comparison function must cause the data
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items in the set to be <i>well-ordered</i>. The comparison function
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must correctly handle any data item values used by the application
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(possibly including zero-length data items). The <b>data</b> and
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<b>size</b> fields of the <a href="../api_java/dbt_class.html">Dbt</a> are the only fields that may be
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used for the purposes of this comparison, and no particular alignment
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of the memory to which the <b>data</b> field refers may be assumed.
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<p>If no comparison function is specified, the data items are compared
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lexically, with shorter data items collating before longer data items.
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<p>The Db.set_dup_compare interface may not be called after the <a href="../api_java/db_open.html">Db.open</a>
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If the database already exists when
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<a href="../api_java/db_open.html">Db.open</a> is called, the information specified to Db.set_dup_compare must
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be the same as that historically used to create the database or
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<p>The Db.set_dup_compare method throws an exception that encapsulates a non-zero error value on
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<p>The Db.set_dup_compare method may fail and throw an exception encapsulating a non-zero error for the following conditions:
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<p><dt>EINVAL<dd>An invalid flag value or parameter was specified.
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<p>The Db.set_dup_compare method may fail and throw an exception for errors specified for other Berkeley DB and C library or system methods.
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If a catastrophic error has occurred, the Db.set_dup_compare method may fail and
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throw a <a href="../api_java/runrec_class.html">DbRunRecoveryException</a>,
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in which case all subsequent Berkeley DB calls will fail in the same way.
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<a href="../api_java/db_class.html">Db</a>
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