Java Mybatis反向关系导致对象重复
我试图用MyBatis 3.2.8映射集合的反向关系。似乎MyBatis复制对象,即使它们具有相同的idJava Mybatis反向关系导致对象重复,java,xml,mybatis,ibatis,relation,Java,Xml,Mybatis,Ibatis,Relation,我试图用MyBatis 3.2.8映射集合的反向关系。似乎MyBatis复制对象,即使它们具有相同的id public class ObjA { private String id; private ArrayList<ObjB> objBs; // Getters, setters ... // Equals based on the id field } public class ObjB { private String id;
public class ObjA {
private String id;
private ArrayList<ObjB> objBs;
// Getters, setters ...
// Equals based on the id field
}
public class ObjB {
private String id;
private ObjA objA;
// Getters, setters ...
// Equals based on the id field
}
映射xml文件
<resultMap id="xx" type="ObjA">
<id column="idA" property="id" />
<collection property="objBs" javaType="ArrayList" ofType="ObjB">
<id column="idB" property="id"/>
<association property="objA" type="ObjA">
<id column="idA" property="id" />
</association>
</collection>
</resultMap>
JUnit测试
ArrayList<ObjA> result = service.getAllObjA();
for(ObjA objA : result) {
for(ObjB objB : objA.getObjBs()) {
assertEquals(objB.getObjA(), objA); // Pass
assertTrue(objB.getObjA() == objA); // Does not pass
}
}
我希望objB.getObjA和objA是objA的相同引用
如何配置结果映射以使其正常工作。您描述的POJO的ObjA和ObjB是循环依赖的
考虑以下示例:让我们有一个艺术家类和一个录音类。他们不需要实现可比较的接口,但我们这样做是因为我们想对这些对象进行排序。或者,可以编写SQL查询来指定所返回行的所需排序顺序
这是艺术课。请注意,艺术家持有其录音集
import java.util.List;
public class Artist implements Comparable {
private int id;
private List<Recording> recordings;
private String name;
public Artist() {}
public Artist(String name) { this.name = name; }
public int compareTo(Object obj) {
Artist r = (Artist) obj;
return name.compareTo(r.name);
}
public int getId() { return id; }
public void setId(int id) { this.id = id; }
public String getName() { return name; }
public void setName(String name) {
this.name = name;
}
public List<Recording> getRecordings() { return recordings; }
public void setRecordings(List<Recording> recordings) {
this.recordings = recordings;
}
}
配置:
映射语句在从SqlMapConfig.XML文件引用的XML文件中定义
这是一个文件,它指定了与我们的艺术家表相关的语句
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE sqlMap
PUBLIC "-//ibatis.apache.org//DTD SQL Map 2.0//EN"
"http://ibatis.apache.org/dtd/sql-map-2.dtd">
<sqlMap namespace="Artist">
<delete id="deleteAll">
delete from artists
</delete>
<insert id="insert" parameterClass="com.ociweb.music.Artist">
insert into artists (name) values (#name#)
<selectKey resultClass="int" keyProperty="id">
select last_insert_id() as id
</selectKey>
</insert>
<resultMap id="result" class="com.ociweb.music.Artist">
<result property="id" column="id"/>
<result property="name" column="name"/>
<!-- This results in N+1 selects. To avoid this, see page 40
in the iBATIS Developer Guide. -->
<result property="recordings" column="id"
select="Recording.getByArtist"/>
</resultMap>
<select id="getById"
parameterClass="java.lang.Integer" resultMap="result">
select * from artists where id=#id#
</select>
<select id="getAll" resultClass="com.ociweb.music.Artist">
select * from artists
</select>
</sqlMap>
下面是一个文件,它指定了与recordings表相关的语句
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE sqlMap
PUBLIC "-//ibatis.apache.org//DTD SQL Map 2.0//EN"
"http://ibatis.apache.org/dtd/sql-map-2.dtd">
<sqlMap namespace="Recording">
<delete id="deleteAll">
delete from recordings
</delete>
<insert id="insert" parameterClass="com.ociweb.music.Recording">
insert into recordings (name, year, artist_id)
values (#name#, #year#, #artist.id#)
<selectKey resultClass="int" keyProperty="id">
select last_insert_id() as id
</selectKey>
</insert>
<resultMap id="resultWithoutArtist" class="com.ociweb.music.Recording">
<result property="id" column="id"/>
<result property="name" column="name"/>
<result property="year" column="year"/>
</resultMap>
<resultMap id="result"
class="com.ociweb.music.Recording" extends="resultWithoutArtist">
<result property="artist" column="artist_id" select="Artist.getById"/>
</resultMap>
<select id="getAll" resultClass="com.ociweb.music.Recording">
select * from recordings
</select>
<!-- resultWithoutArtist is used here to avoid a circular
dependency when Artist.result (in Artist.xml) is used. -->
<select id="getByArtist"
parameterClass="java.lang.Integer" resultMap="resultWithoutArtist">
select * from recordings where artist_id=#artistId#
</select>
<select id="getByYear"
parameterClass="java.lang.Integer" resultMap="result">
select * from recordings where year=#year#
</select>
</sqlMap>
尝试下面的配置和映射,因为非常感谢您的解释非常好的答案!不幸的是,这个解决方案给我带来了一个复杂性问题。我终于找到了一个漫游环境。@Sacha不客气:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE sqlMap
PUBLIC "-//ibatis.apache.org//DTD SQL Map 2.0//EN"
"http://ibatis.apache.org/dtd/sql-map-2.dtd">
<sqlMap namespace="Artist">
<delete id="deleteAll">
delete from artists
</delete>
<insert id="insert" parameterClass="com.ociweb.music.Artist">
insert into artists (name) values (#name#)
<selectKey resultClass="int" keyProperty="id">
select last_insert_id() as id
</selectKey>
</insert>
<resultMap id="result" class="com.ociweb.music.Artist">
<result property="id" column="id"/>
<result property="name" column="name"/>
<!-- This results in N+1 selects. To avoid this, see page 40
in the iBATIS Developer Guide. -->
<result property="recordings" column="id"
select="Recording.getByArtist"/>
</resultMap>
<select id="getById"
parameterClass="java.lang.Integer" resultMap="result">
select * from artists where id=#id#
</select>
<select id="getAll" resultClass="com.ociweb.music.Artist">
select * from artists
</select>
</sqlMap>
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE sqlMap
PUBLIC "-//ibatis.apache.org//DTD SQL Map 2.0//EN"
"http://ibatis.apache.org/dtd/sql-map-2.dtd">
<sqlMap namespace="Recording">
<delete id="deleteAll">
delete from recordings
</delete>
<insert id="insert" parameterClass="com.ociweb.music.Recording">
insert into recordings (name, year, artist_id)
values (#name#, #year#, #artist.id#)
<selectKey resultClass="int" keyProperty="id">
select last_insert_id() as id
</selectKey>
</insert>
<resultMap id="resultWithoutArtist" class="com.ociweb.music.Recording">
<result property="id" column="id"/>
<result property="name" column="name"/>
<result property="year" column="year"/>
</resultMap>
<resultMap id="result"
class="com.ociweb.music.Recording" extends="resultWithoutArtist">
<result property="artist" column="artist_id" select="Artist.getById"/>
</resultMap>
<select id="getAll" resultClass="com.ociweb.music.Recording">
select * from recordings
</select>
<!-- resultWithoutArtist is used here to avoid a circular
dependency when Artist.result (in Artist.xml) is used. -->
<select id="getByArtist"
parameterClass="java.lang.Integer" resultMap="resultWithoutArtist">
select * from recordings where artist_id=#artistId#
</select>
<select id="getByYear"
parameterClass="java.lang.Integer" resultMap="result">
select * from recordings where year=#year#
</select>
</sqlMap>