Ibatis的对象关系映射问题

对于一对多或一对一的映射关系，在实体类里引用的是对象类型，而数据库里使用的是ID，这样就牵涉到OR映射问题。如：

实体类：

public class PetitionLetter {
	private int id;                              //信访件ID
	private String identifier;                   //信访件编号
	private Reporter reporter;                   //举报人
	private LetterInformation letterInformation; //举报信
	private Supervision supervision;             //督办
	private ProcessFlow processFlow;             //处理流程
        //get set 方法省略
}

数据库表：

create table T_PETITIONLETTER
(
  ID                NUMBER(10) not null, 
  IDENTIFIER        VARCHAR2(255),
  REPORTER          NUMBER(10),
  LETTERINFORMATION NUMBER(10),
  SUPERVISION       NUMBER(10),
  PROCESSFLOW       NUMBER(10)
)

查询出所有的PetitionLetter：

 <select id="selectAllPetitionLetter" resultMap="PetitionLetterResult" remapResults="true">
    select * from t_petitionletter
  </select>

  <resultMap id="PetitionLetterResult" class="PetitionLetter">
    <result property="id" column="id"/>
    <result property="identifier" column="identifier"/>
    <result property="reporter" column="reporter" select="selectReporterById"/>
    <result property="letterInformation" column="letterInformation" select="selectLetterInformationById"/>
    <result property="supervision" column="supervision" select="selectSupervisionById"/>
    <result property="processFlow" column="processFlow" select="selectProcessFlowById"/>
  </resultMap>

  <select id="selectProcessFlowById" resultClass="ProcessFlow" parameterClass="int" remapResults="true">
  	select * from t_processflow where id = #id#
  </select>
  
  <select id="selectReporterById" resultClass="Reporter" parameterClass="int">
  	select * from t_reporter where id = #id#
  </select>
  
  <select id="selectLetterInformationById" resultClass="LetterInformation" parameterClass="int">
  	select * from t_letterinformation where id = #id#
  </select>
  
  <select id="selectSupervisionById" resultClass="Supervision" parameterClass="int">
  	select * from t_supervision where id = #id#
  </select>

注：resultMap里把column中经查询得到的数据库id字段传给select里的方法，得到一个实体类对象的数据，返回给property里的实体类，这样不仅查询出PetitionLetter,也查询出了PetitionLetter里引用的实体类对象的相关数据。

插入PetitionLetter记录：

<parameterMap class="PetitionLetter" id="PetitionLetterParam">
    <parameter property="id" jdbcType="NUMBER"/>
  	<parameter property="identifier" jdbcType="VARCHAR2"/>
  	<parameter property="reporter.id" jdbcType="NUMBER"/>
  	<parameter property="letterInformation.id" jdbcType="NUMBER"/>
  	<parameter property="supervision.id" jdbcType="NUMBER"/>
  	<parameter property="processFlow.id" jdbcType="NUMBER"/>
  </parameterMap>

<insert id="insertPetitionLetter" parameterMap="PetitionLetterParam">
  	  <selectKey resultClass="int" keyProperty="id" type="pre">      
           <![CDATA[SELECT SEQ_ID_PETITION.NEXTVAL AS ID FROM DUAL]]>      
      </selectKey> 
    <![CDATA[  
  	insert into t_petitionletter(id, identifier, reporter, letterInformation, 
  	                             supervision, processFlow) values
  	                             (?,?,?,?,?,?)
   ]]>  
  </insert>

注：在后台里插入方法传入的是一个对象，而对象里的引用属性也是对象，而不是int型的ID，所以parameterMap里的property要使用“对象.id”的方式与jdbcType里number类型匹配。