//$Id: TableGenerator.java 11304 2007-03-19 22:06:45Z [email protected] $
package org.hibernate.id;
import java.io.Serializable;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Types;
import java.util.Properties;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.hibernate.HibernateException;
import org.hibernate.LockMode;
import org.hibernate.dialect.Dialect;
import org.hibernate.engine.SessionImplementor;
import org.hibernate.engine.TransactionHelper;
import org.hibernate.mapping.Table;
import org.hibernate.type.Type;
import org.hibernate.util.PropertiesHelper;
/**
* An <tt>IdentifierGenerator</tt> that uses a database
* table to store the last generated value. It is not
* intended that applications use this strategy directly.
* However, it may be used to build other (efficient)
* strategies. The returned type is <tt>Integer</tt>.<br>
* <br>
* The hi value MUST be fetched in a seperate transaction
* to the <tt>Session</tt> transaction so the generator must
* be able to obtain a new connection and commit it. Hence
* this implementation may not be used when Hibernate is
* fetching connections when the user is supplying
* connections.<br>
* <br>
* The returned value is of type <tt>integer</tt>.<br>
* <br>
* Mapping parameters supported: table, column
*
* @see TableHiLoGenerator
* @author Gavin King
*/
public class TableGenerator extends TransactionHelper
implements PersistentIdentifierGenerator, Configurable {
/* COLUMN and TABLE should be renamed but it would break the public API */
/** The column parameter */
public static final String COLUMN = "column";
/** Default column name */
public static final String DEFAULT_COLUMN_NAME = "next_hi";
/** The table parameter */
public static final String TABLE = "table";
/** Default table name */
public static final String DEFAULT_TABLE_NAME = "hibernate_unique_key";
private static final Log log = LogFactory.getLog(TableGenerator.class);
private String tableName;
private String columnName;
private String query;
private String update;
public void configure(Type type, Properties params, Dialect dialect) {
tableName = PropertiesHelper.getString(TABLE, params, DEFAULT_TABLE_NAME);
columnName = PropertiesHelper.getString(COLUMN, params, DEFAULT_COLUMN_NAME);
String schemaName = params.getProperty(SCHEMA);
String catalogName = params.getProperty(CATALOG);
if ( tableName.indexOf( '.' )<0 ) {
tableName = Table.qualify( catalogName, schemaName, tableName );
}
query = "select " +
columnName +
" from " +
dialect.appendLockHint(LockMode.UPGRADE, tableName) +
dialect.getForUpdateString();
update = "update " +
tableName +
" set " +
columnName +
" = ? where " +
columnName +
" = ?";
}
public synchronized Serializable generate(SessionImplementor session, Object object)
throws HibernateException {
int result = ( (Integer) doWorkInNewTransaction(session) ).intValue();
return new Integer(result);
}
public String[] sqlCreateStrings(Dialect dialect) {
return new String[] {
dialect.getCreateTableString() + " " + tableName + " ( " + columnName + " " + dialect.getTypeName(Types.INTEGER) + " )",
"insert into " + tableName + " values ( 0 )"
};
}
public String[] sqlDropStrings(Dialect dialect) {
StringBuffer sqlDropString = new StringBuffer( "drop table " );
if ( dialect.supportsIfExistsBeforeTableName() ) {
sqlDropString.append( "if exists " );
}
sqlDropString.append( tableName ).append( dialect.getCascadeConstraintsString() );
if ( dialect.supportsIfExistsAfterTableName() ) {
sqlDropString.append( " if exists" );
}
return new String[] { sqlDropString.toString() };
}
public Object generatorKey() {
return tableName;
}
public Serializable doWorkInCurrentTransaction(Connection conn, String sql) throws SQLException {
int result;
int rows;
do {
// The loop ensures atomicity of the
// select + update even for no transaction
// or read committed isolation level
sql = query;
SQL.debug(query);
PreparedStatement qps = conn.prepareStatement(query);
try {
ResultSet rs = qps.executeQuery();
if ( !rs.next() ) {
String err = "could not read a hi value - you need to populate the table: " + tableName;
log.error(err);
throw new IdentifierGenerationException(err);
}
result = rs.getInt(1);
rs.close();
}
catch (SQLException sqle) {
log.error("could not read a hi value", sqle);
throw sqle;
}
finally {
qps.close();
}
sql = update;
SQL.debug(update);
PreparedStatement ups = conn.prepareStatement(update);
try {
ups.setInt( 1, result + 1 );
ups.setInt( 2, result );
rows = ups.executeUpdate();
}
catch (SQLException sqle) {
log.error("could not update hi value in: " + tableName, sqle);
throw sqle;
}
finally {
ups.close();
}
}
while (rows==0);
return new Integer(result);
}
}
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