[英]Hibernate count NamedQuery for many-to-many association with the same entity
[英]Hibernate recursive many-to-many association with the same entity
另一个休眠问题...:P
使用Hibernate的Annotations框架,我有一个User
实体。 每个User
可以有一个朋友集合:其他User
的集合。 但是,我还无法弄清楚如何在User
类中创建一个由User
列表组成的多对多关联(使用用户友好中间表)。
这是User类及其注释:
@Entity
@Table(name="tbl_users")
public class User {
@Id
@GeneratedValue
@Column(name="uid")
private Integer uid;
...
@ManyToMany(
cascade={CascadeType.PERSIST, CascadeType.MERGE},
targetEntity=org.beans.User.class
)
@JoinTable(
name="tbl_friends",
joinColumns=@JoinColumn(name="personId"),
inverseJoinColumns=@JoinColumn(name="friendId")
)
private List<User> friends;
}
用户-朋友映射表只有两列,这两列都是tbl_users
表的uid
列的外键。 两列分别是personId
(应该映射到当前用户)和friendId
(指定当前用户的朋友的id)。
问题是,即使我已经预先填充了Friends表,使得系统中的所有用户都是与所有其他用户的朋友,“ friends”字段仍然保持为空。 我什至尝试将关系切换为@OneToMany
,但仍然显示为空(尽管Hibernate调试输出显示SELECT * FROM tbl_friends WHERE personId = ? AND friendId = ?
查询,但SELECT * FROM tbl_friends WHERE personId = ? AND friendId = ?
没有其他)。
关于如何填充此列表的任何想法? 谢谢!
@ManyToMany对自己来说相当令人困惑,因为您通常的建模方式不同于“休眠”方式。 您的问题是您缺少另一个收藏夹。
可以这样考虑-如果要“多对多”映射“作者” /“书”,则需要“书”上的“作者”集合和“作者”上的“书”集合。 在这种情况下,您的“用户”实体代表关系的两端。 因此您需要“我的朋友”和“朋友的”收藏集:
@ManyToMany
@JoinTable(name="tbl_friends",
joinColumns=@JoinColumn(name="personId"),
inverseJoinColumns=@JoinColumn(name="friendId")
)
private List<User> friends;
@ManyToMany
@JoinTable(name="tbl_friends",
joinColumns=@JoinColumn(name="friendId"),
inverseJoinColumns=@JoinColumn(name="personId")
)
private List<User> friendOf;
您仍然可以使用相同的关联表,但是请注意,join / inverseJon列在集合上交换。
“ friends”和“ friendOf”集合可能匹配,也可能不匹配(取决于您的“友谊”是否始终是相互的),您当然不必在API中以这种方式公开它们,但这就是映射的方式它在休眠状态。
实际上,它非常简单,可以通过以下方式实现:
public class Human {
int id;
short age;
String name;
List<Human> relatives;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public short getAge() {
return age;
}
public void setAge(short age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public List<Human> getRelatives() {
return relatives;
}
public void setRelatives(List<Human> relatives) {
this.relatives = relatives;
}
public void addRelative(Human relative){
if(relatives == null)
relatives = new ArrayList<Human>();
relatives.add(relative);
}
}
HBM相同:
<hibernate-mapping>
<class name="org.know.july31.hb.Human" table="Human">
<id name="id" type="java.lang.Integer">
<column name="H_ID" />
<generator class="increment" />
</id>
<property name="age" type="short">
<column name="age" />
</property>
<property name="name" type="string">
<column name="NAME" length="200"/>
</property>
<list name="relatives" table="relatives" cascade="all">
<key column="H_ID"/>
<index column="U_ID"/>
<many-to-many class="org.know.july31.hb.Human" column="relation"/>
</list>
</class>
</hibernate-mapping>
和测试用例
import org.junit.Test;
import org.know.common.HBUtil;
import org.know.july31.hb.Human;
public class SimpleTest {
@Test
public void test() {
Human h1 = new Human();
short s = 23;
h1.setAge(s);
h1.setName("Ratnesh Kumar singh");
Human h2 = new Human();
h2.setAge(s);
h2.setName("Praveen Kumar singh");
h1.addRelative(h2);
Human h3 = new Human();
h3.setAge(s);
h3.setName("Sumit Kumar singh");
h2.addRelative(h3);
Human dk = new Human();
dk.setAge(s);
dk.setName("D Kumar singh");
h3.addRelative(dk);
HBUtil.getSessionFactory().getCurrentSession().beginTransaction();
HBUtil.getSessionFactory().getCurrentSession().save(h1);
HBUtil.getSessionFactory().getCurrentSession().getTransaction().commit();
HBUtil.getSessionFactory().getCurrentSession().beginTransaction();
h1 = (Human)HBUtil.getSessionFactory().getCurrentSession().load(Human.class, 1);
System.out.println(h1.getRelatives().get(0).getName());
HBUtil.shutdown();
}
}
@JoinTable
批注似乎使所接受的答案过于复杂。 稍微简单一些的实现只需要一个mappedBy
。 使用mappedBy
表示拥有的Entity
或属性,它可能应该是referencesTo
因为这将被视为“朋友”。 ManyToMany
关系可以创建非常复杂的图。 使用mappedBy
可以使代码如下:
@Entity
public class Recursion {
@Id @GeneratedValue
private Integer id;
// what entities does this entity reference?
@ManyToMany
private Set<Recursion> referencesTo;
// what entities is this entity referenced from?
@ManyToMany(mappedBy="referencesTo")
private Set<Recursion> referencesFrom;
public Recursion init() {
referencesTo = new HashSet<>();
return this;
}
// getters, setters
}
要使用它,您需要考虑拥有属性是referencesTo
。 您只需要在该属性中放置关系即可对其进行引用。 当您读回Entity
,假设您执行了fetch join
,则JPA将为结果创建集合。 删除实体时,JPA会删除对该实体的所有引用。
tx.begin();
Recursion r0 = new Recursion().init();
Recursion r1 = new Recursion().init();
Recursion r2 = new Recursion().init();
r0.getReferencesTo().add(r1);
r1.getReferencesTo().add(r2);
em.persist(r0);
em.persist(r1);
em.persist(r2);
tx.commit();
// required so that existing entities with null referencesFrom will be removed from cache.
em.clear();
for ( int i=1; i <= 3; ++i ) {
Recursion r = em.createQuery("select distinct r from Recursion r left join fetch r.referencesTo left join fetch r.referencesFrom where id = :id", Recursion.class).setParameter("id", i).getSingleResult();
System.out.println(r + " To=" + Arrays.toString(r.getReferencesTo().toArray()) + " From=" + Arrays.toString(r.getReferencesFrom().toArray()) );
}
tx.begin();
em.createQuery("delete from Recursion where id = 2").executeUpdate();
tx.commit();
// required so that existing entities with referencesTo will be removed from cache.
em.clear();
Recursion r = em.createQuery("select distinct r from Recursion r left join fetch r.referencesTo left join fetch r.referencesFrom where id = :id", Recursion.class).setParameter("id", 1).getSingleResult();
System.out.println(r + " To=" + Arrays.toString(r.getReferencesTo().toArray()) + " From=" + Arrays.toString(r.getReferencesFrom().toArray()) );
它提供以下日志输出(始终检查生成的SQL语句):
Hibernate: create table Recursion (id integer not null, primary key (id))
Hibernate: create table Recursion_Recursion (referencesFrom_id integer not null, referencesTo_id integer not null, primary key (referencesFrom_id, referencesTo_id))
Hibernate: create sequence hibernate_sequence start with 1 increment by 1
Hibernate: alter table Recursion_Recursion add constraint FKsi0wfuwfs0bl19jjpofw4n8pt foreign key (referencesTo_id) references Recursion
Hibernate: alter table Recursion_Recursion add constraint FKarrkuyh2v1j5qnlui2vbpl7tk foreign key (referencesFrom_id) references Recursion
Hibernate: call next value for hibernate_sequence
Hibernate: call next value for hibernate_sequence
Hibernate: call next value for hibernate_sequence
Hibernate: insert into Recursion (id) values (?)
Hibernate: insert into Recursion (id) values (?)
Hibernate: insert into Recursion (id) values (?)
Hibernate: insert into Recursion_Recursion (referencesFrom_id, referencesTo_id) values (?, ?)
Hibernate: insert into Recursion_Recursion (referencesFrom_id, referencesTo_id) values (?, ?)
Hibernate: select distinct recursion0_.id as id1_2_0_, recursion2_.id as id1_2_1_, recursion4_.id as id1_2_2_, references1_.referencesFrom_id as referenc1_3_0__, references1_.referencesTo_id as referenc2_3_0__, references3_.referencesTo_id as referenc2_3_1__, references3_.referencesFrom_id as referenc1_3_1__ from Recursion recursion0_ left outer join Recursion_Recursion references1_ on recursion0_.id=references1_.referencesFrom_id left outer join Recursion recursion2_ on references1_.referencesTo_id=recursion2_.id left outer join Recursion_Recursion references3_ on recursion0_.id=references3_.referencesTo_id left outer join Recursion recursion4_ on references3_.referencesFrom_id=recursion4_.id where id=?
model.Recursion@7bdf6bb7 To=[model.Recursion@1bc53649] From=[]
Hibernate: select distinct recursion0_.id as id1_2_0_, recursion2_.id as id1_2_1_, recursion4_.id as id1_2_2_, references1_.referencesFrom_id as referenc1_3_0__, references1_.referencesTo_id as referenc2_3_0__, references3_.referencesTo_id as referenc2_3_1__, references3_.referencesFrom_id as referenc1_3_1__ from Recursion recursion0_ left outer join Recursion_Recursion references1_ on recursion0_.id=references1_.referencesFrom_id left outer join Recursion recursion2_ on references1_.referencesTo_id=recursion2_.id left outer join Recursion_Recursion references3_ on recursion0_.id=references3_.referencesTo_id left outer join Recursion recursion4_ on references3_.referencesFrom_id=recursion4_.id where id=?
model.Recursion@1bc53649 To=[model.Recursion@42deb43a] From=[model.Recursion@7bdf6bb7]
Hibernate: select distinct recursion0_.id as id1_2_0_, recursion2_.id as id1_2_1_, recursion4_.id as id1_2_2_, references1_.referencesFrom_id as referenc1_3_0__, references1_.referencesTo_id as referenc2_3_0__, references3_.referencesTo_id as referenc2_3_1__, references3_.referencesFrom_id as referenc1_3_1__ from Recursion recursion0_ left outer join Recursion_Recursion references1_ on recursion0_.id=references1_.referencesFrom_id left outer join Recursion recursion2_ on references1_.referencesTo_id=recursion2_.id left outer join Recursion_Recursion references3_ on recursion0_.id=references3_.referencesTo_id left outer join Recursion recursion4_ on references3_.referencesFrom_id=recursion4_.id where id=?
model.Recursion@42deb43a To=[] From=[model.Recursion@1bc53649]
Hibernate: delete from Recursion_Recursion where (referencesTo_id) in (select id from Recursion where id=2)
Hibernate: delete from Recursion_Recursion where (referencesFrom_id) in (select id from Recursion where id=2)
Hibernate: delete from Recursion where id=2
Hibernate: select distinct recursion0_.id as id1_2_0_, recursion2_.id as id1_2_1_, recursion4_.id as id1_2_2_, references1_.referencesFrom_id as referenc1_3_0__, references1_.referencesTo_id as referenc2_3_0__, references3_.referencesTo_id as referenc2_3_1__, references3_.referencesFrom_id as referenc1_3_1__ from Recursion recursion0_ left outer join Recursion_Recursion references1_ on recursion0_.id=references1_.referencesFrom_id left outer join Recursion recursion2_ on references1_.referencesTo_id=recursion2_.id left outer join Recursion_Recursion references3_ on recursion0_.id=references3_.referencesTo_id left outer join Recursion recursion4_ on references3_.referencesFrom_id=recursion4_.id where id=?
model.Recursion@6b739528 To=[] From=[]
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