Hibernate4多对多查询出重复的记录

sunxing007 2013-12-13 01:26:05

很简单很常见的关联关系，我却遇到问题，有工会会员Member和工会俱乐部Club，是多对多关系，如下代码：



@Entity 

@Table(name = "tu_member") 

public class Member extends BaseEntity<Member>{

	private static final long serialVersionUID = 5939777389315777218L;

	private String name;

	private String gender;

	private Date birthday;

	private String company;

	private String department;

	

	@ManyToMany(targetEntity = Club.class, cascade = { CascadeType.ALL }, fetch = FetchType.EAGER)

	@JoinTable(name = "tu_club_member", joinColumns = { @JoinColumn(name = "member_id", nullable = false) }, inverseJoinColumns = { @JoinColumn(name = "club_id", nullable = false) })

	@ForeignKey(name = "none", inverseName = "none")

	private List<Club> clubs;

	

	public List<Club> getClubs() {

		return clubs;

	}

	public void setClubs(List<Club> clubs) {

		this.clubs = clubs;

	}

	public String getName() {

		return name;

	}

。。。。。。



@Entity 

@Table(name = "tu_club") 

public class Club extends BaseEntity<Club>{



	private static final long serialVersionUID = 1058338119416690351L;

	private String name;

	private String company;

	private String description;

	private String coordinator;

	

	@ManyToMany(targetEntity = Member.class)

	@JoinTable(name = "tu_club_member", joinColumns = { @JoinColumn(name = "club_id", nullable = false) }, inverseJoinColumns = { @JoinColumn(name = "member_id", nullable = false) })

	@ForeignKey(name = "none", inverseName = "none")

	private List<Member> members;

	

	public List<Member> getMembers() {

		return members;

	}

	public void setMembers(List<Member> members) {

		this.members = members;

	}

	public String getName() {

		return name;

	}

。。。。。。

Dao和service都是非常普通的写法。
然后我就写了个简单的测试程序。



		Member member = new Member();

		member.setName("Member1");

		member.setBirthday(new Date());

		member.setGender("Male");

		member.setCompany("CSTS");

		member.setDepartment("ICG V");

		

		Club club = new Club();

		club.setCompany("CSTS");

		club.setName("Swimming");

		

		Club club1 = new Club();

		club1.setCompany("CSTS");

		club1.setName("Table Tennies");

		

		List<Club> list = new ArrayList<Club>();

		list.add(club);

		list.add(club1);

		member.setClubs(list);

		memberService.save(member);

		

		Club club2 = new Club();

		club2.setName("Drink");

		club2.setCompany("CSTS");

		member.getClubs().add(club2);

		memberService.save(member);

List<Member> members = memberService.findAll();

这个程序应该出现的结果是一个Member，它关联了3个Club；但是出来的结果吓了我一跳，居然在页面上显示了3条一样的Member。但是数据库只有一条。
我知道出3条的原因是采用左连接造成的：



    select

        this_.id as id11_1_,

        this_.birthday as birthday11_1_,

        this_.company as company11_1_,

        this_.department as department11_1_,

        this_.gender as gender11_1_,

        this_.name as name11_1_,

        clubs2_.member_id as member1_11_3_,

        club3_.id as club2_13_3_,

        club3_.id as id10_0_,

        club3_.company as company10_0_,

        club3_.coordinator as coordina3_10_0_,

        club3_.description as descript4_10_0_,

        club3_.name as name10_0_ 

    from

        tu_member this_ 

    left outer join

        tu_club_member clubs2_ 

            on this_.id=clubs2_.member_id 

    left outer join

        tu_club club3_ 

            on clubs2_.club_id=club3_.id

请问我错在哪里？该怎么配置才能只出现一条？

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花谢尊前不敢香 2013-12-13

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return this.getSession().createCriteria(Member.class).returnMaps().list(); 改为这样应该也可以。

sunxing007 2013-12-13

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然后我看到别人给的解决方法是: return this.getSession().createCriteria(Member.class).setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY).setFetchMode("clubs", FetchMode.JOIN).list();

sunxing007 2013-12-13

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引用 6 楼 hjw506848887 的回复:

把club类上的@JoinTable配置去掉试试。。。。

谢谢关注. 我早上又试验了３个小时,　我发现是由于查询的方式引起的. return this.getSession().createQuery("from Member").list();//这样就不会重复. return this.getSession().createCriteria(Member.class).list();//这样就会重复. 不知道有什么解释.

灰太狼的太太太爷爷 2013-12-13

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把club类上的@JoinTable配置去掉试试。。。。

灰太狼的太太太爷爷 2013-12-13

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引用 4 楼 sunxing007 的回复:

[quote=引用 1 楼 hjw506848887 的回复:] 应该是因为你的club查询时自动加载了member，一共三条club，所以也会查询出三条member。不知道你页面上和后台部分内容是怎么样写的啊。。。

是一个Member加入了3个俱乐部Club, 现在我查Member列表, 并顺带把他们所属的Club查出来. 后台代码都是非常通用的Query.list(), Criteria.list()之类的. 页面代码和本文描述的问题没有关系.[/quote]如果后台没写错，看打印的sql语言，我觉得还是你配置出问题了。。。

sunxing007 2013-12-13