joincolumn.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.sql.SQLException;

import java.util.StringTokenizer;


/**
 * Subclasses of this class represent columns from another table that we
 * want included in our PersistentObject.  These are not columns that are
 * used in the actual join (ie. "Table1.Col1 = Table2.Col1") between tables.
 * <p>
 * The column alias is important since the real column name may match one in
 * the main table.
 */
public abstract class JoinColumn
  {

  protected String i_columnName   = null;
  protected String i_columnAlias  = null;
  protected String i_setter       = null;

  /* ===============  Static Variables  =============== */

  protected static Class s_class = String.class;


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

  public JoinColumn()
    {
    super();
    }


  /**
   * Construct a JoinColumnInstance that is ready to be used.
   *
   * @param columnName a value of type 'String' - can include alias like
   *                   this: "Name PersonName"
   * @param setter a value of type 'String'
   */
  public JoinColumn(
      String columnName,
      String setter)
    {
    this.setColumnName(columnName);
    i_setter = setter;
    }

  /**
   * Construct a JoinColumn instance that is ready to be used.
   *
   * @param columnName a value of type 'String'
   * @param columnAlias a value of type 'String' - This can be important if
   *                    the main table has a matching column name.
   * @param setter a value of type 'String'
   */
  public JoinColumn(
      String columnName,
      String columnAlias,
      String setter)
    {
    i_columnName = columnName;
    i_columnAlias = columnAlias;
    i_setter = setter;
    }


  /**
   * This is usually overridden by subclasses to explicitly specify the type
   * of object to be retrieved from the result set in JDBCHelper.
   *
   * @param helper a value of type 'JDBCHelper'
   * @return a value of type 'Object'
   * @exception SQLException if an error occurs
   */
  public Object getColumnValueFrom(JDBCHelper helper)
          throws SQLException
    {
    return helper.getObject(i_columnAlias);
    }

  public abstract Class getColumnClass();


  public String getColumnName()
    {
    return i_columnName;
    }
  public void setColumnName(String name)
    {
    StringTokenizer st = new StringTokenizer(name, " ");
    if (st.hasMoreTokens())
        {
        i_columnName = st.nextToken();
        }
    else
        {
        throw new ConfigurationException("Invalid table name in " + this);
        }
    if (st.hasMoreTokens())
        {
        i_columnAlias = st.nextToken();
        }
    else
        {
        i_columnAlias = i_columnName;
        }
    } // setColumnName(aString)


  public String getColumnAlias()
    {
    return i_columnAlias;
    }
  public void setColumnAlias(String alias)
    {
    i_columnAlias = alias;
    }


  public String getSetter()
    {
    return i_setter;
    }
  public void setSetter(String setter)
    {
    i_setter = setter;
    }


  /**
   * Copy the value of my column to the appropriate attribute for this
   * persistent object.
   *
   * @param helper a value of type 'JDBCHelper'
   * @param aPO a value of type 'PersistentObject'
   * @exception SQLException if an error occurs
   */
  public void copyColumnValueToPersistentObject(JDBCHelper helper,
                                                PersistentObject aPO)
          throws SQLException
    {
    if (i_setter != null &&
        i_setter.length() > 0)
        {
        Object value = this.getColumnValueFrom(helper);
        this.setValueTo(value, aPO);
        }
    }



  private void setValueTo(Object aValue,
                          PersistentObject aPO)
    {
    AbstractColumnSpec.setValueTo(aValue,
                                  aPO,
                                  this.getSetter(),
                                  this.getColumnClass());
    }


  protected void buildSelectColumnString(StringBuffer sqlBuffer,
                                         String tableAlias)
    {
    sqlBuffer.append(tableAlias);
    sqlBuffer.append(".");
    sqlBuffer.append(i_columnName);
    if (!i_columnName.equals(i_columnAlias))
        {
        sqlBuffer.append(" AS ");
        sqlBuffer.append(i_columnAlias);
        }
    }


  } // JoinColumn