AnnotationException：引用dayHibernate的外鍵…錯誤的列數。 應該是3

Question

我只想從兩個表中從標准員工db MySQL中獲取數據：

EMPLOYEES {
   EMP_NO, -- PK
   BIRTH_DATE,
   ....
}

TITLES {
   EMP_NO, -- PK, and FK to EMPLOYEES
   TITLE, -- PK
   FROM_DATE, -- PK
   TO_DATE,
   ....
}

這是很多列的關鍵：

@Embeddable
public class TitleId implements Serializable {
    @Column(name = "emp_no")
    private long empNumber;

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

    @Column(name = "from_date")
    private java.sql.Date fromDate;

// constructor, hascode, setter, getter
// ................

}

並且有實體：

第一實體

@Entity(name = "Title")
@Table(name = "titles")
public class Title implements Serializable {

    @EmbeddedId
    private TitleId titleId;

    @Column(name = "to_date")
    private java.sql.Date toDate;

    @OneToMany(mappedBy = "title")
    private List<Employee> employees = new ArrayList<>();

// constructor, setter, getter

}

第二實體

@Entity
@Table(name = "employees")
public class Employee {

    @Id
    @Column(name = "emp_no")
    private long empNo;

    @ManyToOne(optional = false)
    @JoinColumn(name = "emp_no", insertable = false, updatable = false)
    private Title title;

 //   setter, getter, constructor, other coluns
}

EmployeeDao是：

    List employees = session.createQuery("FROM Employee").list();
    for (Iterator iterator = employees.iterator(); iterator.hasNext();){
        Employee employee = (Employee) iterator.next();
        System.out.print("First Name: " + employee.getFirstName());
        System.out.print("  Last Name: " + employee.getLastName());
    }

當我嘗試獲取此數據時，會有下一個異常

AnnotationException: A Foreign key refering dayHibernate.Title from dayHibernate.Employee has the wrong number of column. should be 3

如何從這兩個表中獲取數據並避免異常？ 幫我pl

Answer 1

在所引用實體上使用復合鍵時，不能將@JoinColumn與@ManyToOne一起使用。 異常確實說明了一切，Employee試圖僅使用emp_no來引用Title，但復合鍵中還有兩個字段。

我認為這是整個實體模型的設計問題。 由於TitleId包含Employee的主鍵，因此Title實體應該不能與Employee建立多對一關系，但是Employee應該可以擁有許多標題。

由於Emp_no在復合鍵中，並且是外鍵，因此您應該可以使用@MapsId， 請參閱此示例 。

這對我有用：

雇員

@Entity @Table(name = "employees") public class Employee {

    @Id
    @Column(name = "emp_no")
    private long empNo;

    @OneToMany(mappedBy="employee")
    private List<Title> titles = new ArrayList<>();

    ... }

TitleId

@Embeddable
public class TitleId implements Serializable {

    private static final long serialVersionUID = 1L;

    @Column(name = "emp_no")
    private long empNumber;

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

    @Column(name = "from_date")
    private java.sql.Date fromDate;
}

標題

@Entity(name = "Title")
@Table(name = "titles")
public class Title implements Serializable {

    @EmbeddedId
    private TitleId titleId;

    @Column(name = "to_date")
    private java.sql.Date toDate;

    @MapsId("empNumber")
    @JoinColumn(name = "emp_no")
    @ManyToOne
    private Employee employee;

}

Answer 2

將@JoinColumns添加到Employee表

@Entity
@Table(name = "employees")
public class Employee {

    @Id
    @Column(name = "emp_no")
    private long empNo;

    @ManyToOne(optional = false)
      @JoinColumns ({
      @JoinColumn(name="emp_number", referencedColumnName = "emp_no"),
      @JoinColumn(name="title", referencedColumnName = "title"),
      @JoinColumn(name="from_date", referencedColumnName = "from_date")
    })
    private Title title;

 //   setter, getter, constructor, other coluns
}