Question

I have two entities, let's name them University and Student, Student is unidirectional ManyToOne with University they both extends base class BasicUUIDEntity:

@MappedSuperclass
public class BasicUUIDEntity implements Serializable {

    protected UUID id;

    @Id
    @Column(name = "id", columnDefinition = "binary(16)")
    @GeneratedValue(generator = "uuid2")
    @GenericGenerator(name = "uuid2", strategy = "uuid2")
    public UUID getId() {
        return id;
    }

    public void setId(UUID id) {
        this.id = id;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        BasicUUIDEntity that = (BasicUUIDEntity) o;

        return id == null || id.equals(that.id);
    }

    @Override
    public int hashCode() {
        return id != null ? id.hashCode() : 0;
    }
}

The structure of Student and University doesn't really matters, the important things is: Student.class:

@Entity
@Table(name = "students")
public static class Student extends BasicUUIDEntity {

    private University univ;

    @ManyToOne(fetch = FetchType.EAGER)
    @JoinColumn(name = "univ_id", referencedColumnName = "id")
    public University getUniversity() {
        return univ;
    }

    public void setUniversity(University univ) {
        this.univ = univ;
    }
}

University.class:

@Entity
@Table(name = "universities")
public static class University extends BasicUUIDEntity {
    //of course it does contain some fields, but they are strings, etc.
}

The tables are created as follows:

CREATE TABLE students
(
  id                 BINARY(16) NOT NULL,
  univ_id            BINARY(16),
  PRIMARY KEY (id),
  CONSTRAINT FK_STUDENT_UNIV
  FOREIGN KEY (univ_id) REFERENCES memory_type (id)
    ON DELETE SET NULL
)
  ENGINE = InnoDB
  DEFAULT CHARSET = utf8;

CREATE TABLE universities
(
  id                 BINARY(16) NOT NULL,
  PRIMARY KEY (id)
)
  ENGINE = InnoDB
  DEFAULT CHARSET = utf8;

The Issue is sometimes, on really rare occasions Hibernate doesn't extract that University entity along with Student, meaning that when I do student.getUniversity() it returns null, and in debugger it is also null. BUT the students table contains exactly the same univ_id as expected University of this student, and so does university contains that id. I am completely sure that hibernate session is not closed, and I've tried to execute exactly the same query as hibernate does, and it does return expected id of the university, joins them, etc. The thing is that most of the time It does work well, and such issue happens very rarely due to unknown reasons, what is more strange is that the table does contains that id, so it seems like it is not an MySQL issue. Also worth mention, I am using Spring Data JPA. Have anyone encountered such behavior? Could it be due to Inheritance/Data JPA/Java 9/Anything other?

PS. Please ignore any typo in the code, it is just an example

Versions:

Hibernate: 5.2.12.Final, 
Spring Data JPA: 2.0.5.RELEASE,
HikariCP: 2.7.8,
MySQL connector: 6.0.6,
Java: 9
MySQL: Ver 14.14 Distrib 5.7.21

Answer 1

解决，最后

<强> TL;博士

将fetch = FetchType.LAZY置于ManyToOne关系，因此在我的示例中它变为：

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "univ_id", referencedColumnName = "id")
public University getUniversity() {
    return univ;
}

<强>描述

我仍然不确定为什么它会像这样，但似乎Hibernate根本不提取many-to-one关系，如果他们渴望的话。它有一定的意义，因为这样会有循环依赖，但我认为PersistenceSet将处理这些问题。更奇怪的是 - 如果我使用Long而不是UUID，那么相同的结构实际上无需提取即可。

Hibernate sometimes doesn't extract uuid referenced entity

1 个答案:

Hibernate sometimes doesn&#39;t extract uuid referenced entity

1 个答案:

Hibernate sometimes doesn't extract uuid referenced entity