/*
* Column.java 2005-7-30
*
* 版权所有: 自由思考组织(FTO)软件团队 2000-2005, 保留所有权利.
* 这个软件是自由思考组织(FTO)软件团队开发的，如果要使用这个软件，请首先阅读并接受许可协议。
*
* Copyright 2000-2005 FTO Software Team, Inc. All Rights Reserved.
* This software is the proprietary information of FTO Software Team, Inc.
* Use is subject to license terms.
*
* FTO站点：http://www.free-think.org
*/
package org.fto.jthink.jdbc;
import org.fto.jthink.lang.ObjectBuffered;
import org.fto.jthink.lang.StringBuffered;
/**
* 列, 用于描述Select语句返回的数据列. 构建的列可以是标准的表字段,也可以是一个表达式或一个SQL子查询.
*
* <pre>
* 以下是可以构建的列的几种形式:
* 表字段: fieldName1, fieldName2, fieldName3 AS tmpfieldName3
* 表达式: (fieldName1*100-50) AS tmpfieldName1, (3+2-5) AS tmpfieldName2
* SQL了查询: (select table2.fieldName1 from table2 where table2.id = table1.id) AS tmpfieldName1
* </pre>
*
* <p><pre><b>
* 历史更新记录:</b>
* 2005-07-30 创建此类型
* </pre></p>
*
*
* @author wenjian
* @version 1.0
* @since JThink 1.0
*/
public class Column implements java.io.Serializable{
private static final long serialVersionUID = 1L;
String columnName=null;
Object columnValue=null;
/**
* 建立列, 列值可以是字段名称,也可以是一个表达式,但请不要直接写SQL语句串,这样会降低可移植性
*
* <pre>
* 以下是此构造方法构建列的几种方式:
* new Column(fieldName1, fieldName1), 构建出的列: fieldName1
* new Column(tmpfieldName1, fieldName1), 构建出的列: (fieldName1) AS tmpfieldName1
* new Column(tmpfieldName1, fieldName1*0.50), 构建出的列: (fieldName1*0.50) AS tmpfieldName1
* new Column(tmpfieldName1,3+2-5), 构建出的列: (3+2-5) AS tmpfieldName1
* new Column(fieldName1,(String)null), 构建出的列: tmpfieldName1
*
* </pre>
*
* @param columnName 列名称
* @param columnValue 列值
*/
public Column(String columnName, String columnValue){
if (columnName == null){
throw new IllegalArgumentException(
"The column name cannot be null.");
}
this.columnName = columnName;
this.columnValue = columnValue;
}
/**
* 建立列,只给出列名称,构建出的列也只包含列名,
* 比如: new Column(fieldName1), 构建出的列是:fieldName1
*
* @param columnName 列名称
*/
public Column(String columnName){
if (columnName == null){
throw new IllegalArgumentException(
"The column name cannot be null.");
}
this.columnName = columnName;
this.columnValue = columnName;
}
/**
* 建立列,列值为一个SQL语句.此构造器将构建一个包含子查询的列
*
* <pre>
* Condition userNameCDN = new Condition();
* userNameCDN.setItem(new ConditionItem("Users.UserId", "=", "Departments.UserId", true));
* SQL userNameSQL = sqlBuilder.constructSQLForSelect("Users", new Column[]{new Column("UserName")}, userNameCDN);
*
* new Column("UserName", userNameSQL), 构建出的列:(SELECT UserName FROM Users WHERE Users.UserId = Departments.UserId ) AS UserName
*
* </pre>
*
* @param columnName 列名称
* @param sql SQL类型的实例
*/
public Column(String columnName, SQL sql){
if (columnName == null){
throw new IllegalArgumentException(
"The column name cannot be null.");
}
this.columnName = columnName;
this.columnValue = sql;
}
/**
* 返回列名称
*
* @return 列名称
*/
public String getColumnName(){
return columnName;
}
/**
* 返回列值
*
* @return 列值
*/
public Object getColumnValue(){
return columnValue;
}
/**
* 检查是否是简单列, 即：columnValue==null || columnName==columnValue的列
*/
public boolean isSimpleColumn(){
return columnValue==null || columnName==columnValue;
}
/**
* 返回列的SQL语句形式
*
* @return 描述此列的SQL语句
*
*/
public SQL getColumn(){
StringBuffered column=null;
ObjectBuffered values=null;
if(columnValue instanceof java.lang.String){
if(columnName==columnValue){
return new SQL(SQL.UNDEFINED, columnName, null);
}else{
column = new StringBuffered(4).append("(").append(columnValue).append(") AS ").append(columnName);
}
}else{
SQL sql = (SQL)columnValue;
StringBuffered sqlStatement = sql.getSQLStatement();
column = new StringBuffered(3+sqlStatement.size()).append("(").append(sqlStatement).append(") AS ").append(columnName);
values = sql.getValueBuffered();
}
return new SQL(SQL.UNDEFINED, column, values);
}
}