许多对同一类型实体的关系 [英] Many to many relationship for same type entity
问题描述
我有一个实体，如下所示。我很好奇，如果可以创建一个关系，我将用这个例子来描述： 之后，我将Michael作为JSON响应进行检索，并在响应中提供Julia。但是当我找回朱莉娅的时候，她的朋友组是空的。我想通过拯救友谊的一方来创造双向的友谊关系。我想让迈克尔在Julia的朋友身上做任何其他的操作。我认为它必须由Hibernate管理。
@ToString（exclude =friends）//编辑：这2个排除
@Id
@GeneratedValue（strategy = GenerationType.AUTO）
@列（name =id）
私人长ID;
@Column（name =name，unique = true）
私有字符串名称;
@JsonIgnoreProperties（friends）//编辑：将阻止无限递归
@ManyToMany（cascade = CascadeType.ALL）
@JoinTable（name =FRIENDSHIP，
joinColumns = @JoinColumn（name =person_id，
referencedColumnName =id），
inverseJoinColumns = @JoinColumn（name =friend_id，
referencedColumnName =id ））
private Set< Person>朋友;
这是我的服务层代码，友谊：
@Override
public Person addFriend（String personName，String friendName）
throws FriendshipExistsException，PersonNotFoundException {
Person person = retrieveWithName（personName）;
Person friend = retrieveWithName（friendName）;
if（！person.getFriends（）。contains（friend））{
person.getFriends（）。add（friend）;
return repository.save（person）;
}
else {
抛出new FriendshipExistsException（personName，friendName）;
$ / code $ / pre
lockquote
相关问题：
N + 1查询双向许多到许多相同的实体类型
更新了源代码并且此版本正常工作。
解决方案
//创建图形以帮助hibernate创建带外连接的查询。
@NamedEntityGraph（name =graph.Person.friends，
attributeNodes = @NamedAttributeNode（value =friends））
class Person {}
interface PersonRepository扩展了JpaRepository< Person，Long> {
//使用指定的图表，它将在同一查询中获取所有朋友
@Override
@EntityGraph（value =graph.Person.friends）
Person findOne长ID）;
$ b @Override
public Person addFriend（String personName，String friendName）
throws FriendshipExistsException，PersonNotFoundException {
Person person = retrieveWithName（personName）;
Person friend = retrieveWithName（friendName）;
if（！person.getFriends（）。contains（friend））{
person.getFriends（）。add（friend）;
friend.getFriends（）。add（person）; //需要设置关系
return repository.save（person）; //只使用一种保存方法，它可以节省级联
}的朋友其他{
抛出新的FriendshipExistsException（personName，friendName）;
}
}
如果你检查你的hibernate日志，你会看到：
Hibernate：insert into person（name，id）values（？，？）
Hibernate：insert into person（name，id）values（？，？）
Hibernate：插入友情（person_id，friend_id）values（？，？）
Hibernate：插入友谊（person_id，friend_id）值（？，？）
I have an entity as below. I am curious if it is possible to create a relationship as I will be describing with the example:
- I am creating 2 Person entities Michael and Julia.
- I am adding Julia to Michael's friends set.
After that I am retrieving Michael as a JSON response and Julia is available in the response. But when I am retrieving Julia, her friends set is empty. I want to create the bidirectional friendship relation by saving just one side of the friendship. I would like to get Michael on Julia's friends set without doing any other operations. I think that it must be managed by Hibernate. Is it possible and how should I do it?
@ToString(exclude = "friends") // EDIT: these 2 exclusion necessary
@EqualsAndHashCode(exclude = "friends")
public class Person{
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "id")
private Long id;
@Column(name = "name",unique = true)
private String name;
@JsonIgnoreProperties("friends") // EDIT: will prevent the infinite recursion
@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name = "FRIENDSHIP",
joinColumns = @JoinColumn(name = "person_id",
referencedColumnName = "id"),
inverseJoinColumns = @JoinColumn(name = "friend_id",
referencedColumnName = "id"))
private Set<Person> friends;
Here is my service layer code for creating a friendship:
@Override
public Person addFriend(String personName, String friendName)
throws FriendshipExistsException, PersonNotFoundException {
Person person = retrieveWithName(personName);
Person friend = retrieveWithName(friendName);
if(!person.getFriends().contains(friend)){
person.getFriends().add(friend);
return repository.save(person);
}
else{
throw new FriendshipExistsException(personName, friendName);
}
}
Related Question:
N+1 query on bidirectional many to many for same entity type
Updated the source code and this version is working properly.
解决方案 // Creating a graph to help hibernate to create a query with outer join.
@NamedEntityGraph(name="graph.Person.friends",
attributeNodes = @NamedAttributeNode(value = "friends"))
class Person {}
interface PersonRepository extends JpaRepository<Person, Long> {
// using the named graph, it will fetch all friends in same query
@Override
@EntityGraph(value="graph.Person.friends")
Person findOne(Long id);
}
@Override
public Person addFriend(String personName, String friendName)
throws FriendshipExistsException, PersonNotFoundException {
Person person = retrieveWithName(personName);
Person friend = retrieveWithName(friendName);
if(!person.getFriends().contains(friend)){
person.getFriends().add(friend);
friend.getFriends().add(person); // need to setup the relation
return repository.save(person); // only one save method is used, it saves friends with cascade
} else {
throw new FriendshipExistsException(personName, friendName);
}
}
If you check your hibernate logs, you will see:
Hibernate: insert into person (name, id) values (?, ?)
Hibernate: insert into person (name, id) values (?, ?)
Hibernate: insert into friendship (person_id, friend_id) values (?, ?)
Hibernate: insert into friendship (person_id, friend_id) values (?, ?)
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