gsg/JAVA/Positioning.html

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    <div class="sect1" lang="en" xml:lang="en">
      <div class="titlepage">
        <div>
          <div>
            <h2 class="title" style="clear: both"><a id="Positioning"></a>Getting Records Using the Cursor</h2>
          </div>
        </div>
      </div>
      <div class="toc">
        <dl>
          <dt>
            <span class="sect2">
              <a href="Positioning.html#cursorsearch">Searching for Records</a>
            </span>
          </dt>
          <dt>
            <span class="sect2">
              <a href="Positioning.html#getdups">Working with Duplicate Records</a>
            </span>
          </dt>
        </dl>
      </div>
      <p>
        To iterate over database records, from the first record to
        the last, simply open the cursor and then use the
            <code class="methodname">Cursor.getNext()</code>


        method.

        For example:
     </p>
      <a id="java_cursor3"></a>
      <pre class="programlisting">package db.GettingStarted;

import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.Cursor;
import com.sleepycat.db.LockMode;
import com.sleepycat.db.OperationStatus;

...

Cursor cursor = null;
try {
    ...
    Database myDatabase = null;
    // Database open omitted for brevity
    ...

    // Open the cursor.
    cursor = myDatabase.openCursor(null, null);

    // Cursors need a pair of DatabaseEntry objects to operate. These hold
    // the key and data found at any given position in the database.
    DatabaseEntry foundKey = new DatabaseEntry();
    DatabaseEntry foundData = new DatabaseEntry();

    // To iterate, just call getNext() until the last database record has been
    // read. All cursor operations return an OperationStatus, so just read
    // until we no longer see OperationStatus.SUCCESS
    while (cursor.getNext(foundKey, foundData, LockMode.DEFAULT) ==
        OperationStatus.SUCCESS) {
        // getData() on the DatabaseEntry objects returns the byte array
        // held by that object. We use this to get a String value. If the
        // DatabaseEntry held a byte array representation of some other data
        // type (such as a complex object) then this operation would look
        // considerably different.
        String keyString = new String(foundKey.getData(), "UTF-8");
        String dataString = new String(foundData.getData(), "UTF-8");
        System.out.println("Key | Data : " + keyString + " | " +
                       dataString + "");
    }
} catch (DatabaseException de) {
    System.err.println("Error accessing database." + de);
} finally {
    // Cursors must be closed.
    cursor.close();
}</pre>
      <p>
    To iterate over the database from the last record to the first,
    instantiate the cursor, and then
    use <code class="methodname">Cursor.getPrev()</code> until you read the first record in
    the database. For example:
    </p>
      <a id="java_cursor4"></a>
      <pre class="programlisting">package db.GettingStarted;

import com.sleepycat.db.Cursor;
import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.LockMode;
import com.sleepycat.db.OperationStatus;

...

Cursor cursor = null;
Database myDatabase = null;
try {
    ...
    // Database open omitted for brevity
    ...

    // Open the cursor.
    cursor = myDatabase.openCursor(null, null);

    // Get the DatabaseEntry objects that the cursor will use.
    DatabaseEntry foundKey = new DatabaseEntry();
    DatabaseEntry foundData = new DatabaseEntry();

    // Iterate from the last record to the first in the database
    while (cursor.getPrev(foundKey, foundData, LockMode.DEFAULT) ==
        OperationStatus.SUCCESS) {

        String theKey = new String(foundKey.getData(), "UTF-8");
        String theData = new String(foundData.getData(), "UTF-8");
        System.out.println("Key | Data : " +  theKey + " | " + theData + "");
    }
} catch (DatabaseException de) {
    System.err.println("Error accessing database." + de);
} finally {
    // Cursors must be closed.
    cursor.close();
}</pre>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="cursorsearch"></a>Searching for Records</h3>
            </div>
          </div>
        </div>
        <p>
        You can use cursors to search for database records. You can search based
        on just a key, or you can search based on both the key and the data.
        You can also perform partial matches if your database supports sorted
        duplicate sets. In all cases, the key and data parameters of these
        methods are filled with the key and data values of the database record
        to which the cursor is positioned as a result of the search.
      </p>
        <p>
        Also, if the search fails, then cursor's state is left unchanged
        and
            <code class="literal">OperationStatus.NOTFOUND</code>

        is returned.


      </p>
        <p>
        The following <code class="classname">Cursor</code> methods allow you to
        perform database searches:
      </p>
        <div class="itemizedlist">
          <ul type="disc">
            <li>
              <p>
            <code class="methodname">Cursor.getSearchKey()</code>

           </p>
              <p>
            Moves the cursor to the first record in the database with
            the specified key.
          </p>
            </li>
            <li>
              <p>
            <code class="methodname">Cursor.getSearchKeyRange()</code>

          </p>
              <p>
            <span>Identical to

                <code class="methodname">Cursor.getSearchKey()</code>
            unless you are using the BTree access. In this case, the cursor
            moves</span>


            to the first record in the database whose
            key is greater than or equal to the specified key. This comparison
            is determined by the
                <span>comparator</span>

            that you provide for the database. If no
                <span>comparator</span>

                is provided, then the default

                lexicographical sorting is used.
          </p>
              <p>
            For example, suppose you have database records that use the
            following
                <span>Strings</span>

            as keys:
          </p>
              <pre class="programlisting">Alabama
Alaska
Arizona</pre>
              <p>
            Then providing a search key of <code class="literal">Alaska</code> moves the
            cursor to the second key noted above. Providing a key of
            <code class="literal">Al</code> moves the cursor to the first key (<code class="literal">Alabama</code>), providing
            a search key of <code class="literal">Alas</code> moves the cursor to the second key
            (<code class="literal">Alaska</code>), and providing a key of <code class="literal">Ar</code> moves the
            cursor to the last key (<code class="literal">Arizona</code>).
          </p>
            </li>
            <li>
              <p>
            <code class="methodname">Cursor.getSearchBoth()</code>

           </p>
              <p>
            Moves the cursor to the first record in the database that uses
            the specified key and data.
          </p>
            </li>
            <li>
              <p>
            <code class="methodname">Cursor.getSearchBothRange()</code>

          </p>
              <p>
            Moves the cursor to the first record in the database whose key matches the specified
            key and whose data is
            greater than or equal to the specified data. If the database supports
            duplicate records, then on matching the key, the cursor is moved to
            the duplicate record with the smallest data that is greater than or
            equal to the specified data.
          </p>
              <p>
            For example,

                <span>suppose your database uses BTree
                and it has </span>
            database records that use the following key/data pairs:
          </p>
              <pre class="programlisting">Alabama/Athens
Alabama/Florence
Alaska/Anchorage
Alaska/Fairbanks
Arizona/Avondale
Arizona/Florence </pre>
              <p>then providing:</p>
              <div class="informaltable">
                <table border="1" width="80%">
                  <colgroup>
                    <col />
                    <col />
                    <col />
                  </colgroup>
                  <thead>
                    <tr>
                      <th>a search key of ...</th>
                      <th>and a search data of ...</th>
                      <th>moves the cursor to ...</th>
                    </tr>
                  </thead>
                  <tbody>
                    <tr>
                      <td>Alaska</td>
                      <td>Fa</td>
                      <td>Alaska/Fairbanks</td>
                    </tr>
                    <tr>
                      <td>Arizona</td>
                      <td>Fl</td>
                      <td>Arizona/Florence</td>
                    </tr>
                    <tr>
                      <td>Alaska</td>
                      <td>An</td>
                      <td>Alaska/Anchorage</td>
                    </tr>
                  </tbody>
                </table>
              </div>
            </li>
          </ul>
        </div>
        <p>
        For example, assuming a database containing sorted duplicate records of
        U.S. States/U.S Cities key/data pairs (both as
            <span>Strings),</span>

        then the following code fragment can be used to position the cursor
        to any record in the database and print its key/data values:

      </p>
        <a id="java_cursor5"></a>
        <pre class="programlisting">package db.GettingStarted;

import com.sleepycat.db.Cursor;
import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.LockMode;
import com.sleepycat.db.OperationStatus;

...

// For this example, hard code the search key and data
String searchKey = "Alaska";
String searchData = "Fa";

Cursor cursor = null;
Database myDatabase = null;
try {
    ...
    // Database open omitted for brevity
    ...

    // Open the cursor.
    cursor = myDatabase.openCursor(null, null);

    DatabaseEntry theKey =
         new DatabaseEntry(searchKey.getBytes("UTF-8"));
    DatabaseEntry theData =
         new DatabaseEntry(searchData.getBytes("UTF-8"));

    // Open a cursor using a database handle
    cursor = myDatabase.openCursor(null, null);

    // Perform the search
    OperationStatus retVal = cursor.getSearchBothRange(theKey, theData,
                                                       LockMode.DEFAULT);
    // NOTFOUND is returned if a record cannot be found whose key
    // matches the search key AND whose data begins with the search data.
    if (retVal == OperationStatus.NOTFOUND) {
        System.out.println(searchKey + "/" + searchData +
                           " not matched in database " +
                           myDatabase.getDatabaseName());
    } else {
        // Upon completing a search, the key and data DatabaseEntry
        // parameters for getSearchBothRange() are populated with the
        // key/data values of the found record.
        String foundKey = new String(theKey.getData(), "UTF-8");
        String foundData = new String(theData.getData(), "UTF-8");
        System.out.println("Found record " + foundKey + "/" + foundData +
                           "for search key/data: " + searchKey +
                           "/" + searchData);
    }

} catch (Exception e) {
    // Exception handling goes here
} finally {
   // Make sure to close the cursor
   cursor.close();
}</pre>
      </div>
      <div class="sect2" lang="en" xml:lang="en">
        <div class="titlepage">
          <div>
            <div>
              <h3 class="title"><a id="getdups"></a>Working with Duplicate Records</h3>
            </div>
          </div>
        </div>
        <p>
        A record is a duplicate of another record if the two records share the
        same key. For duplicate records, only the data portion of the record is unique.
      </p>
        <p>
        Duplicate records are supported only for the BTree or Hash access methods.
        For information on configuring your database to use duplicate records,
        see <a class="xref" href="btree.html#duplicateRecords" title="Allowing Duplicate Records">Allowing Duplicate Records</a>.
      </p>
        <p>
		If your database supports duplicate records, then it can potentially
		contain multiple records that share the same key.


        <span>By default, normal database
		get operations will only return the first such record in a set
		of duplicate records. Typically, subsequent duplicate records are
        accessed using a cursor.
        </span>

        The following
            <span><code class="methodname">Cursor</code> methods</span>


        are interesting when working with databases that support duplicate records:
	  </p>
        <div class="itemizedlist">
          <ul type="disc">
            <li>
              <p>
            <span>
                <code class="methodname">Cursor.getNext()</code>,
                <code class="methodname">Cursor.getPrev()</code>
            </span>

          </p>
              <p>
            Shows the next/previous record in the database, regardless of
            whether it is a duplicate of the current record. For an example of
            using these methods, see <a class="xref" href="Positioning.html" title="Getting Records Using the Cursor">Getting Records Using the Cursor</a>.
          </p>
            </li>
            <li>
              <p>
            <code class="methodname">Cursor.getSearchBothRange()</code>

          </p>
              <p>
            Useful for seeking the cursor to a specific record, regardless of
            whether it is a duplicate record. See <a class="xref" href="Positioning.html#cursorsearch" title="Searching for Records">Searching for Records</a> for more
            information.
          </p>
            </li>
            <li>
              <p>
            <span>
                <code class="methodname">Cursor.getNextNoDup()</code>,
                <code class="methodname">Cursor.getPrevNoDup()</code>
            </span>

          </p>
              <p>
            Gets the next/previous non-duplicate record in the database.  This
            allows you to skip over all the duplicates in a set of duplicate
            records. If you call
                <span><code class="methodname">Cursor.getPrevNoDup()</code>,</span>

            then the cursor is positioned to the last record for the previous
            key in the database.  For example, if you have the following records
            in your database:
          </p>
              <pre class="programlisting">Alabama/Athens
Alabama/Florence
Alaska/Anchorage
Alaska/Fairbanks
Arizona/Avondale
Arizona/Florence</pre>
              <p>
          and your cursor is positioned to <code class="literal">Alaska/Fairbanks</code>,
          and you then call
                <span><code class="methodname">Cursor.getPrevNoDup()</code>,</span>

          then the cursor is positioned to Alabama/Florence. Similarly, if
          you call
                <span><code class="methodname">Cursor.getNextNoDup()</code>,</span>


          then the cursor is positioned to the first record corresponding to
          the next key in the database.
          </p>
              <p>
            If there is no next/previous key in the database, then
                <code class="literal">OperationStatus.NOTFOUND</code>

            is returned, and the cursor is left unchanged.
          </p>
            </li>
            <li>
              <p>


          </p>
              <p>

            Gets the

                <span>next</span>
            record that shares the current key. If the
            cursor is positioned at the last record in the duplicate set and
            you call
                <span><code class="methodname">Cursor.getNextDup()</code>,</span>


            then
                <code class="literal">OperationStatus.NOTFOUND</code>

            is returned and the cursor is left unchanged.
            <span>
                Likewise, if you call
                <code class="methodname">getPrevDup()</code> and the
                cursor is positioned at the first record in the duplicate set, then
                <code class="literal">OperationStatus.NOTFOUND</code> is returned and the
                cursor is left unchanged.
             </span>
          </p>
            </li>
            <li>
              <p>
                <code class="methodname">Cursor.count()</code>
              </p>
              <p>Returns the total number of records that share the current key.</p>
            </li>
          </ul>
        </div>
        <p>
        For example, the following code fragment positions a cursor to a key


        <span>and displays it and all its
        duplicates.</span>

        <span>Note that the following code fragment assumes that the database contains
        only String objects for the keys and data.</span>
      </p>
        <a id="java_cursor6"></a>
        <pre class="programlisting">package db.GettingStarted;

import com.sleepycat.db.Cursor;
import com.sleepycat.db.Database;
import com.sleepycat.db.DatabaseEntry;
import com.sleepycat.db.DatabaseException;
import com.sleepycat.db.LockMode;
import com.sleepycat.db.OperationStatus;

...

Cursor cursor = null;
Database myDatabase = null;
try {
    ...
    // Database open omitted for brevity
    ...

    // Create DatabaseEntry objects
    // searchKey is some String.
    DatabaseEntry theKey = new DatabaseEntry(searchKey.getBytes("UTF-8"));
    DatabaseEntry theData = new DatabaseEntry();

    // Open a cursor using a database handle
    cursor = myDatabase.openCursor(null, null);

    // Position the cursor
    // Ignoring the return value for clarity
    OperationStatus retVal = cursor.getSearchKey(theKey, theData,
                                                 LockMode.DEFAULT);

    // Count the number of duplicates. If the count is greater than 1,
    // print the duplicates.
    if (cursor.count() &gt; 1) {
        while (retVal == OperationStatus.SUCCESS) {
            String keyString = new String(theKey.getData(), "UTF-8");
            String dataString = new String(theData.getData(), "UTF-8");
            System.out.println("Key | Data : " +  keyString + " | " +
                               dataString + "");

            retVal = cursor.getNextDup(theKey, theData, LockMode.DEFAULT);
        }
    }
} catch (Exception e) {
    // Exception handling goes here
} finally {
   // Make sure to close the cursor
   cursor.close();
}</pre>
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