JPA Hibernate惰性获取属性和一个查询

Question

考虑以下实体：

@Entity(name = "user")
public class UserEntity {

    @Id
    @Column(name = "id", columnDefinition = "serial")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "name")
    private String name;

    @OneToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "user_role", joinColumns = @JoinColumn(name = "user_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "role_id", referencedColumnName = "id"))
    private List<RoleEntity> roles = new ArrayList<>();

}

@Entity(name = "role")
@NamedEntityGraph(
        name = "role.entity_graph",
        attributeNodes = {
                @NamedAttributeNode(value = "permissions")
        })
public class RoleEntity {

    @Id
    @Column(name = "id", columnDefinition = "serial")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "name")
    private String name;


    @ManyToMany(fetch = FetchType.LAZY)
    @JoinTable(name = "role_permission", joinColumns = @JoinColumn(name = "role_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "permission_id", referencedColumnName = "id"))
    private List<PermissionEntity> permissions = new ArrayList<>();

}

@Entity(name = "permission")
public class PermissionEntity {

    @Id
    @Column(name = "id", columnDefinition = "serial")
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "name")
    private String name;


}

用户实体的角色应该被延迟获取。问题是，当使用角色时（调用getter），hibernate会通过对每个角色的查询和对每个角色的每个权限的查询来获取它们，从而导致n1问题。

因此，我的问题是：如何通过一个查询获取用户角色？我可以利用角色属性的实体图吗？

注意：我已经试过使用@Fetch：

@Fetch(FetchMode.JOIN)
@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(name = "role_permission", joinColumns = @JoinColumn(name = "role_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "permission_id", referencedColumnName = "id"))
private List<PermissionEntity> permissions = new ArrayList<>();

这不管用。然而，与@BatchSize一起，它可以作为例外。

@Fetch(FetchMode.JOIN)
@BatchSize(size = 1000)
@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(name = "role_permission", joinColumns = @JoinColumn(name = "role_id", referencedColumnName = "id"), inverseJoinColumns = @JoinColumn(name = "permission_id", referencedColumnName = "id"))
private List<PermissionEntity> permissions = new ArrayList<>();

不过，我对这个解决方案不满意。为什么我需要添加@BatchSize？




Answer 1

我认为使用子图可能会对您有所帮助。看看Thorben Janssen在他的网站上的描述：具有多个子图的实体图，引用：

@NamedEntityGraph(
    name = "graph.AuthorBooksPublisherEmployee", 
    attributeNodes = @NamedAttributeNode(value = "books", subgraph = "subgraph.book"), 
    subgraphs = {
        @NamedSubgraph(name = "subgraph.book", 
                       attributeNodes = @NamedAttributeNode(value = "publisher", subgraph = "subgraph.publisher")),
        @NamedSubgraph(name = "subgraph.publisher", 
                       attributeNodes = @NamedAttributeNode(value = "employees")) })