autoincrementcounter.java

derby database source code.good for you.

/*

   Derby - Class org.apache.derby.impl.sql.execute.AutoincrementCounter

   Copyright 2000, 2004 The Apache Software Foundation or its licensors, as applicable.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

 */

package org.apache.derby.impl.sql.execute;
import org.apache.derby.iapi.services.sanity.SanityManager;
import	org.apache.derby.iapi.sql.dictionary.TableDescriptor;
import org.apache.derby.iapi.sql.dictionary.ColumnDescriptor;
import org.apache.derby.iapi.sql.dictionary.DataDictionary;
import org.apache.derby.iapi.store.access.TransactionController;
import org.apache.derby.iapi.error.StandardException;
import org.apache.derby.catalog.UUID;
import org.apache.derby.iapi.reference.SQLState;


/**
 * AutoincrementCounter is a not so general counter for the specific purposes
 * of autoincrement columns. It can be thought of as an in-memory autoincrement
 * column.
 * The counting or incrementing is done in fashion identical to the
 * AUTOINCREMENTVALUE in SYSCOLUMNS.
 * <p>
 * To create a counter, the user must call the constructor with a start value,
 * increment and optionally a final value. In addition the caller must specify
 * the schema name, table name and column name uniquely identifying the
 * counter. 
 * <p>
 * When a counter is created it is in an invalid state-- to initialize it, the
 * user must call either  <i>update</i> or <i>reset(false)</i>. The value of a
 * counter can be changed by either calling reset or update. 

 * @author manish
 */
public class AutoincrementCounter 
{

	private Long start;
	private long increment;
	private String identity;
	private long finalValue;
	private String schemaName;
	private String tableName;
	private String columnName;
	// maintains state.
	private long counter;
	private int columnPosition;
	private boolean initialized = false;

	/**
	 * constructor 
	 * @param 	start		The start value of the counter; is a java object as
	 * 			it can also be null.
	 * @param   increment	how much to increment the counter by.
	 * @param	finalValue	the finalvalue of the counter. used by reset
	 * @param 	s
	 * @param   t
	 * @param	c
	 */
	public AutoincrementCounter(Long start, long increment, long finalValue,
								String s, String t, String c, int position)
	{
		this.increment = increment;
		this.start = start;
		this.initialized = false;
		this.identity = makeIdentity(s,t,c);
		this.finalValue = finalValue;
		this.schemaName = s;
		this.tableName = t;
		this.columnName = c;
		this.columnPosition = position;
		//		System.out.println("aic created with " + this);
	}

	/**
	 * make a unique key for the counter.
	 */
	public static String makeIdentity(String s, String t, String c)
	{
		return s + "." + t + "." + c;
	}

	/**
	 * make a unique key for the counter.
	 */
	public static String makeIdentity(TableDescriptor td, ColumnDescriptor cd)
	{
		return td.getSchemaName() + "." + td.getName() + 
				"." + cd.getColumnName();
	}

	/**
	 * reset to the counter to the beginning or the end.
	 * 
	 * @param 	begin	if TRUE reset to beginning and mark it uninitialized.
	 */
	public void reset(boolean begin)
	{
		if (begin == true)
			initialized = false;
		else
		{
			counter = finalValue;
			initialized = true;
		}
		//		System.out.println("counter reset to " + this);

	}

	/**
	 * update the counter.
	 * 
	 * @param 	t		update the counter to this value.
	 */
	public long update(long t)
	{
		counter = t;
		//		System.out.println("counter updated to " + this);
		initialized = true;
		return counter;
	}

	/**
	 * update the counter to its next value.
	 * 
	 * @exception	StandardException	if the counter has not yet been
	 * initialized and the Start value is NULL.
	 */
	public long update() throws StandardException
	{
		long counterVal;

		if (initialized == false)
		{
			// The first time around, counter simply gets the start
			// value. 
			initialized = true;
			
			if (start == null)
			{
				throw StandardException.newException(
											SQLState.LANG_AI_COUNTER_ERROR);
			}
			counter = start.longValue();			
		}	
		else
		{
			counter = counter + increment;
		}
		//		System.out.println("counter updated to " + this);
		return counter;
	}

	/**
	 * get the current value of the counter. An uninitialized counter means the
	 * current value is NULL.
	 */
	public Long getCurrentValue()
	{
		if (initialized == false)
			return null;
		return new Long(counter);
	}
	
	/**
	 * return the identity of the counter.
	 */
	public String getIdentity()
	{
		return identity;
	}

	/**
	 * flush a counter to disk; i.e write the current value of the counter into
	 * the row in SYSCOLUMNS.
	 * 
	 * @param	tc			TransactionController to use
	 * @param	dd			DataDictionary to use.
	 * @param	tableUUID	I might have the table name but I need more
	 * information 
	 * @exception	StandardException standard cloudscape exception.
	 */
	public void flushToDisk(TransactionController tc, DataDictionary dd,
							UUID tableUUID)
	       throws StandardException
	{
		dd.setAutoincrementValue(tc, tableUUID, columnName, counter, true);
	}

	/**
	 * get the column position in the table for which this counter has been
	 * created. 
	 * @return the position of the corresponding column in the table (1-based)
	 */
	public int getColumnPosition()
	{
		return columnPosition;
	}

	/**
	 * get the start value
	 * @return the initial value of the counter
	 */
	public Long getStartValue()
	{
		return start;
	}

	public String toString()
	{
		return "counter: " + identity + " current: " + counter 
			+ " start: " + start + 
			" increment: " + increment + " final: " + finalValue;
	}	
}