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package javax.sql.rowset.spi;

import javax.sql.RowSet;

import java.sql.SQLException;

/**

 * Defines a framework that allows applications to use a manual decision tree

 * to decide what should be done when a synchronization conflict occurs.

 * Although it is not mandatory for

 * applications to resolve synchronization conflicts manually, this

 * framework provides the means to delegate to the application when conflicts

 * arise.

 * <p>

 * Note that a conflict is a situation where the <code>RowSet</code> object's original

 * values for a row do not match the values in the data source, which indicates that

 * the data source row has been modified since the last synchronization. Note also that

 * a <code>RowSet</code> object's original values are the values it had just prior to the

 * the last synchronization, which are not necessarily its initial values.

 * <p>

 *

 * <H2>Description of a <code>SyncResolver</code> Object</H2>

 *

 * A <code>SyncResolver</code> object is a specialized <code>RowSet</code> object

 * that implements the <code>SyncResolver</code> interface.

 * It <b>may</b> operate as either a connected <code>RowSet</code> object (an

 * implementation of the <code>JdbcRowSet</code> interface) or a connected

 * <code>RowSet</code> object (an implementation of the

 * <code>CachedRowSet</code> interface or one of its subinterfaces). For information

 * on the subinterfaces, see the

 * <a href="../package-summary.html"><code>javax.sql.rowset</code></a> package

 * description. The reference implementation for <code>SyncResolver</code> implements

 * the <code>CachedRowSet</code> interface, but other implementations

 * may choose to implement the <code>JdbcRowSet</code> interface to satisfy

 * particular needs.

 * <P>

 * After an application has attempted to synchronize a <code>RowSet</code> object with

 * the data source (by calling the <code>CachedRowSet</code>

 * method <code>acceptChanges</code>), and one or more conflicts have been found,

 * a rowset's <code>SyncProvider</code> object creates an instance of

 * <code>SyncResolver</code>. This new <code>SyncResolver</code> object has

 * the same number of rows and columns as the

 * <code>RowSet</code> object that was attempting the synchronization. The

 * <code>SyncResolver</code> object contains the values from the data source that caused

 * the conflict(s) and <code>null</code> for all other values.

 * In addition, it contains information about each conflict.

 * <P>

 *

 * <H2>Getting and Using a <code>SyncResolver</code> Object</H2>

 *

 * When the method <code>acceptChanges</code> encounters conflicts, the

 * <code>SyncProvider</code> object creates a <code>SyncProviderException</code>

 * object and sets it with the new <code>SyncResolver</code> object. The method

 * <code>acceptChanges</code> will throw this exception, which

 * the application can then catch and use to retrieve the

 * <code>SyncResolver</code> object it contains. The following code snippet uses the

 * <code>SyncProviderException</code> method <code>getSyncResolver</code> to get

 * the <code>SyncResolver</code> object <i>resolver</i>.

 * <PRE>

 *     } catch (SyncProviderException spe) {

 *         SyncResolver resolver = spe.getSyncResolver();

 *     ...

 *     }

 * </PRE>

 * <P>

 * With <i>resolver</i> in hand, an application can use it to get the information

 * it contains about the conflict or conflicts.  A <code>SyncResolver</code> object

 * such as <i>resolver</i> keeps

 * track of the conflicts for each row in which there is a conflict.  It also places a

 * lock on the table or tables affected by the rowset's command so that no more

 * conflicts can occur while the current conflicts are being resolved.

 * <P>

 * The following kinds of information can be obtained from a <code>SyncResolver</code>

 * object:

 * <P>

 * The <code>SyncProvider</code> interface defines four constants

 * describing states that may occur. Three

 * constants describe the type of operation (update, delete, or insert) that a

 * <code>RowSet</code> object was attempting to perform when a conflict was discovered,

 * and the fourth indicates that there is no conflict.

 * These constants are the possible return values when a <code>SyncResolver</code> object

 * calls the method <code>getStatus</code>.

 * <PRE>

 * </PRE>

 * <P>

 * A conflict exists when a value that a <code>RowSet</code> object has changed

 * and is attempting to write to the data source

 * has also been changed in the data source since the last synchronization.  An

 * application can call the <code>SyncResolver</code> method

 * <code>getConflictValue</code > to retrieve the

 * value in the data source that is the cause of the conflict because the values in a

 * <code>SyncResolver</code> object are the conflict values from the data source.

 * <PRE>

 *     java.lang.Object conflictValue = resolver.getConflictValue(2);

 * </PRE>

 * Note that the column in <i>resolver</i> can be designated by the column number,

 * as is done in the preceding line of code, or by the column name.

 * <P>

 * With the information retrieved from the methods <code>getStatus</code> and

 * <code>getConflictValue</code>, the application may make a determination as to

 * which value should be persisted in the data source. The application then calls the

 * <code>SyncResolver</code> method <code>setResolvedValue</code>, which sets the value

 * to be persisted in the <code>RowSet</code> object and also in the data source.

 * <PRE>

 *     resolver.setResolvedValue("DEPT", 8390426);

 * </PRE>

 * In the preceding line of code,

 * the column name designates the column in the <code>RowSet</code> object

 * that is to be set with the given value. The column number can also be used to

 * designate the column.

 * <P>

 * An application calls the method <code>setResolvedValue</code> after it has

 * resolved all of the conflicts in the current conflict row and repeats this process

 * for each conflict row in the <code>SyncResolver</code> object.

 * <P>

 *

 * <H2>Navigating a <code>SyncResolver</code> Object</H2>

 *

 * Because a <code>SyncResolver</code> object is a <code>RowSet</code> object, an

 * application can use all of the <code>RowSet</code> methods for moving the cursor

 * to navigate a <code>SyncResolver</code> object. For example, an application can

 * use the <code>RowSet</code> method <code>next</code> to get to each row and then

 * call the <code>SyncResolver</code> method <code>getStatus</code> to see if the row

 * contains a conflict.  In a row with one or more conflicts, the application can

 * iterate through the columns to find any non-null values, which will be the values

 * from the data source that are in conflict.

 * <P>

 * To make it easier to navigate a <code>SyncResolver</code> object, especially when

 * there are large numbers of rows with no conflicts, the <code>SyncResolver</code>

 * interface defines the methods <code>nextConflict</code> and

 * <code>previousConflict</code>, which move only to rows

 * that contain at least one conflict value. Then an application can call the

 * <code>SyncResolver</code> method <code>getConflictValue</code>, supplying it

 * with the column number, to get the conflict value itself. The code fragment in the

 * next section gives an example.

 *

 * <H2>Code Example</H2>

 *

 * The following code fragment demonstrates how a disconnected <code>RowSet</code>

 * object <i>crs</i> might attempt to synchronize itself with the

 * underlying data source and then resolve the conflicts. In the <code>try</code>

 * block, <i>crs</i> calls the method <code>acceptChanges</code>, passing it the

 * <code>Connection</code> object <i>con</i>.  If there are no conflicts, the

 * changes in <i>crs</i> are simply written to the data source.  However, if there

 * is a conflict, the method <code>acceptChanges</code> throws a

 * <code>SyncProviderException</code> object, and the

 * <code>catch</code> block takes effect.  In this example, which

 * illustrates one of the many ways a <code>SyncResolver</code> object can be used,

 * the <code>SyncResolver</code> method <code>nextConflict</code> is used in a

 * <code>while</code> loop. The loop will end when <code>nextConflict</code> returns

 * <code>false</code>, which will occur when there are no more conflict rows in the

 * <code>SyncResolver</code> object <i>resolver</i>. In This particular code fragment,

 * <i>resolver</i> looks for rows that have update conflicts (rows with the status

 * <code>SyncResolver.UPDATE_ROW_CONFLICT</code>), and the rest of this code fragment

 * executes only for rows where conflicts occurred because <i>crs</i> was attempting an

 * update.

 * <P>

 * After the cursor for <i>resolver</i> has moved to the next conflict row that

 * has an update conflict, the method <code>getRow</code> indicates the number of the

 * current row, and

 * the cursor for the <code>CachedRowSet</code> object <i>crs</i> is moved to

 * the comparable row in <i>crs</i>. By iterating

 * through the columns of that row in both <i>resolver</i> and <i>crs</i>, the conflicting

 * values can be retrieved and compared to decide which one should be persisted. In this

 * code fragment, the value in <i>crs</i> is the one set as the resolved value, which means

 * that it will be used to overwrite the conflict value in the data source.

 *

 *     try {

 *

 *         crs.acceptChanges(con);

 *

 *     } catch (SyncProviderException spe) {

 *

 *         SyncResolver resolver = spe.getSyncResolver();

 *

 *         Object crsValue;  // value in the RowSet object

 *         Object resolverValue:  // value in the SyncResolver object

 *         Object resolvedValue:  // value to be persisted

 *

 *         while(resolver.nextConflict())  {

 *             if(resolver.getStatus() == SyncResolver.UPDATE_ROW_CONFLICT)  {

 *                 int row = resolver.getRow();

 *                 crs.absolute(row);

 *

 *                 int colCount = crs.getMetaData().getColumnCount();

 *                 for(int j = 1; j <= colCount; j++) {

 *                     if (resolver.getConflictValue(j) != null)  {

 *                         crsValue = crs.getObject(j);

 *                         resolverValue = resolver.getConflictValue(j);

 *                         . . .

 *                         // compare crsValue and resolverValue to determine

 *                         // which should be the resolved value (the value to persist)

 *                         resolvedValue = crsValue;

 *

 *                         resolver.setResolvedValue(j, resolvedValue);

 *                      }

 *                  }

 *              }

 *          }

 *      }

 * }</PRE>

 * @author  Jonathan Bruce

 */

public interface SyncResolver extends RowSet {

    /**

     * Indicates that a conflict occurred while the <code>RowSet</code> object was

     * attempting to update a row in the data source.

     * The values in the data source row to be updated differ from the

     * <code>RowSet</code> object's original values for that row, which means that

     * the row in the data source has been updated or deleted since the last

     * synchronization.

     */

     public static int UPDATE_ROW_CONFLICT = 0;

    /**

     * Indicates that a conflict occurred while the <code>RowSet</code> object was

     * attempting to delete a row in the data source.

     * The values in the data source row to be updated differ from the

     * <code>RowSet</code> object's original values for that row, which means that

     * the row in the data source has been updated or deleted since the last

     * synchronization.

     */

    public static int DELETE_ROW_CONFLICT = 1;

   /**

    * Indicates that a conflict occurred while the <code>RowSet</code> object was

    * attempting to insert a row into the data source.  This means that a

    * row with the same primary key as the row to be inserted has been inserted

    * into the data source since the last synchronization.

    */

    public static int INSERT_ROW_CONFLICT = 2;

    /**

     * Indicates that <b>no</b> conflict occured while the <code>RowSet</code> object

     * was attempting to update, delete or insert a row in the data source. The values in

     * the <code>SyncResolver</code> will contain <code>null</code> values only as an indication

     * that no information in pertitent to the conflict resolution in this row.

     */

    public static int NO_ROW_CONFLICT = 3;

    /**

     * Retrieves the conflict status of the current row of this <code>SyncResolver</code>,

     * which indicates the operation

     * the <code>RowSet</code> object was attempting when the conflict occurred.

     *

     * @return one of the following constants:

     *         <code>SyncResolver.UPDATE_ROW_CONFLICT</code>,

     *         <code>SyncResolver.DELETE_ROW_CONFLICT</code>,

     *         <code>SyncResolver.INSERT_ROW_CONFLICT</code>, or

     *         <code>SyncResolver.NO_ROW_CONFLICT</code>

     */

    public int getStatus();

    /**

     * Retrieves the value in the designated column in the current row of this

     * <code>SyncResolver</code> object, which is the value in the data source

     * that caused a conflict.

     *

     * @param index an <code>int</code> designating the column in this row of this

     *        <code>SyncResolver</code> object from which to retrieve the value

     *        causing a conflict

     * @return the value of the designated column in the current row of this

     *         <code>SyncResolver</code> object

     * @throws SQLException if a database access error occurs

     */

    public Object getConflictValue(int index) throws SQLException;

    /**

     * Retrieves the value in the designated column in the current row of this

     * <code>SyncResolver</code> object, which is the value in the data source

     * that caused a conflict.

     *

     * @param columnName a <code>String</code> object designating the column in this row of this

     *        <code>SyncResolver</code> object from which to retrieve the value

     *        causing a conflict

     * @return the value of the designated column in the current row of this

     *         <code>SyncResolver</code> object

     * @throws SQLException if a database access error occurs

     */

    public Object getConflictValue(String columnName) throws SQLException;

    /**

     * Sets <i>obj</i> as the value in column <i>index</i> in the current row of the

     * <code>RowSet</code> object that is being synchronized. <i>obj</i>

     * is set as the value in the data source internally.

     *

     * @param index an <code>int</code> giving the number of the column into which to

     *        set the value to be persisted

     * @param obj an <code>Object</code> that is the value to be set in the

     *        <code>RowSet</code> object and persisted in the data source

     * @throws SQLException if a database access error occurs

     */

    public void setResolvedValue(int index, Object obj) throws SQLException;

    /**

     * Sets <i>obj</i> as the value in column <i>columnName</i> in the current row of the

     * <code>RowSet</code> object that is being synchronized. <i>obj</i>

     * is set as the value in the data source internally.

     *

     * @param columnName a <code>String</code> object giving the name of the column

     *        into which to set the value to be persisted

     * @param obj an <code>Object</code> that is the value to be set in the

     *        <code>RowSet</code> object and persisted in the data source

     * @throws SQLException if a database access error occurs

     */

    public void setResolvedValue(String columnName, Object obj) throws SQLException;

    /**

     * Moves the cursor down from its current position to the next row that contains

     * a conflict value. A <code>SyncResolver</code> object's

     * cursor is initially positioned before the first conflict row; the first call to the

     * method <code>nextConflict</code> makes the first conflict row the current row;

     * the second call makes the second conflict row the current row, and so on.

     * <p>

     * A call to the method <code>nextConflict</code> will implicitly close

     * an input stream if one is open and will clear the <code>SyncResolver</code>

     * object's warning chain.

     *

     * @return <code>true</code> if the new current row is valid; <code>false</code>

     *         if there are no more rows

     * @throws SQLException if a database access error occurs or the result set type

     *     is <code>TYPE_FORWARD_ONLY</code>

     *

     */

    public boolean nextConflict() throws SQLException;

    /**

     * Moves the cursor up from its current position to the previous conflict

     * row in this <code>SyncResolver</code> object.

     * <p>

     * A call to the method <code>previousConflict</code> will implicitly close

     * an input stream if one is open and will clear the <code>SyncResolver</code>

     * object's warning chain.

     *

     * @return <code>true</code> if the cursor is on a valid row; <code>false</code>

     *     if it is off the result set

     * @throws SQLException if a database access error occurs or the result set type

     *     is <code>TYPE_FORWARD_ONLY</code>

     */

    public boolean previousConflict() throws SQLException;

}