updatesqlbuilder.java

把java对象映射成数据库表中的一条记录

/*
 *
 * The contents of this file are subject to the Mozilla Public License
 * Version 1.1 (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.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS"
 * basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
 * License for the specific language governing rights and limitations under
 * the License.
 *
 * The Original Code is jRelationalFramework.
 *
 * The Initial Developer of the Original Code is is.com.
 * Portions created by is.com are Copyright (C) 2000 is.com.
 * All Rights Reserved.
 *
 * Contributor(s): Jonathan Carlson ([e-mail])
 * Contributor(s): ____________________________________
 *
 * Alternatively, the contents of this file may be used under the terms of
 * the GNU General Public License (the "GPL") or the GNU Lesser General
 * Public license (the "LGPL"), in which case the provisions of the GPL or
 * LGPL are applicable instead of those above.  If you wish to allow use of
 * your version of this file only under the terms of either the GPL or LGPL
 * and not to allow others to use your version of this file under the MPL,
 * indicate your decision by deleting the provisions above and replace them
 * with the notice and other provisions required by either the GPL or LGPL
 * License.  If you do not delete the provisions above, a recipient may use
 * your version of this file under either the MPL or GPL or LGPL License.
 *
 */
package com.is.jrf;


import com.is.util.sql.JDBCHelper;

import java.util.List;
import java.util.ArrayList;
import java.util.Iterator;


/**
 *  Instances of this class build SQL to do UPDATE statements.
 */
public class UpdateSQLBuilder
        extends SQLBuilder
  {

  /* ===============  Constructors  =============== */

  /**
   * This constructor throws an exception.
   */
  public UpdateSQLBuilder()
    {
    super();
    }

  public UpdateSQLBuilder(AbstractDomain domain)
    {
    super(domain);
    }



  /**
   * Build SQL to update a row using the columnSpecs.
   *
   * @param aPO a value of type 'PersistentObject'
   * @param columnSpecs a value of type 'List'
   * @return a value of type 'String'
   */
  public String buildSQL(PersistentObject aPO,
                         String tableName,
                         List columnSpecs)
    {
    ColumnSpec aColumnSpec = null;
    ColumnSpec pkColumnSpec = null;
    ColumnSpec lockingColumnSpec = null;

    if (i_dbPolicy == null)
        {
        throw new DatabaseException(
            "The DatabasePolicy has not been set for " + this);
        }

    StringBuffer sqlBuffer = new StringBuffer();
    sqlBuffer.append(" UPDATE ");
    sqlBuffer.append(tableName);
    sqlBuffer.append(" SET ");

    // Create an assignment expression for each column
    Iterator iterator = columnSpecs.iterator();
    while (iterator.hasNext())
        {
        aColumnSpec = (ColumnSpec)iterator.next();
        if (aColumnSpec.isPrimaryKey())
            {
            pkColumnSpec = aColumnSpec; // save for later
            }
        else // not a primary key
            {
            sqlBuffer.append(
                aColumnSpec.getColumnName());
            sqlBuffer.append(" = ");
            if (aColumnSpec.isOptimisticLock())
                {
                lockingColumnSpec = aColumnSpec; // save for later
                if (aColumnSpec instanceof TimestampColumnSpec)
                    {
                    sqlBuffer.append(i_dbPolicy.timestampFunction());
                    }
                else // Assume it's an IntegerColumnSpec
                    {
                    Integer oldVersion =
                            (Integer) aColumnSpec.getValueFrom(aPO);
                    Integer newVersion = new Integer(oldVersion.intValue()+1);
                    sqlBuffer.append(aColumnSpec.formatForSql(newVersion,
                                                              i_dbPolicy));
                    }
                }
            else // it's not an optimistic lock
                {
                sqlBuffer.append(
                    aColumnSpec.getSqlValueFrom(aPO,
                                                i_dbPolicy));
                }
            if (iterator.hasNext())
                {
                sqlBuffer.append(", ");
                }
            } // else not a primary key
        } // while

    // Create the WHERE clause
    sqlBuffer.append(" WHERE ");
    sqlBuffer.append(
        pkColumnSpec.buildWhereClause(aPO,
                                      ColumnSpec.EQUALS,
                                      tableName,
                                      i_dbPolicy));

    // Append to WHERE statement if we have an optimistic lock.
    if (lockingColumnSpec != null)
        {
        // If object was changed (probably by someone else) since last being
        // read, this will prevent the update from occurring.
        sqlBuffer.append(" AND ");
        sqlBuffer.append(
            lockingColumnSpec.getFullyQualifiedColumnName(tableName));
        sqlBuffer.append(" = ");
        sqlBuffer.append(
            lockingColumnSpec.getSqlValueFrom(aPO, i_dbPolicy));
        }

    return sqlBuffer.toString();
    } // buildSQL(PersistentObject)


  } // UpdateSQLBuilder