Question

我在Employee和SkillSet表之间存在多对多关系，每个关系都有额外的列numberOfYears

employeeId  skillSetId  numberOfYears 
10          101         2

我是JPA的新手，无法定义具有关系的实体。我应该为Employee_SkillSet表定义一个新的实体类吗？或者我可以在Employee和SkillSet类中定义多对多的关系吗？我在哪里指定numberOfYears列？

编辑：似乎重复，但我明确要求使用@IdClass，其中一个实体是@MappedSuperclass，因此必须同时定义ID实例和引用的实体对象。

Answer 1

由于你需要为元组（Employee，SkillSet）添加一个额外的字段，你必须创建另一个实体。

@Entity
public class Employee implements Serializable {
    private @Id Long id;

    @OneToMany(mappedBy="employee")
    private List<EmployeeSkillSet> skillSets;
}

@Entity
public class SkillSet implements Serializable {
    private @Id Long id;
}

@Entity
public class EmployeeSkillSet implements Serializable {
    private @Id Long id;
    private @ManyToOne Employee employee;
    private @ManyToOne SkillSet skillSet;
    private @Basic int numberOfYears;
}

当然，您可以选择使用@IdClass来制作（＆＃34;员工＆＃34;，＆＃34;技能组＆＃34;）EmployeeSkillSet的主键，如下所示：< / p>

@Entity @IdClass(EmployeeSkillSet.Key.class)
public class EmployeeSkillSet implements Serializable {

    private @Id @ManyToOne Employee employee;
    private @Id @ManyToOne SkillSet skillSet;
    private @Basic int numberOfYears;

    public static class Key implements Serializable {
        private Long employee; // plus getter+setter
        private Long skillSet; // plus getter+setter
        // plus hashCode, equals
    }
}

Answer 2

虽然您可以使用@ManyToMany注释更好地出于性能原因定义两个多对一关系，以便为多对多关系建模。

你需要4个工件，有

员工实体
SkillSet实体
EmployeeSkillSet Relation实体（此处可指定numberOfYears列）
EmployeeSkillSetPK（EmployeeSkillSet关系实体的主键）

代码将是这样的

<强>员工

:: Now execute the rest of the arguments, if any:
shift
if @%1 == @ goto :eof
set command=
:BuildCommand
if @%1 == @ goto :CommandFinished
set "command=%command% %1"
shift
goto :BuildCommand
:CommandFinished
%command%

<强>技能组

package <your_package>;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

/**
 *
 */
@Entity
@Table(name="EMPLOYEE")
public class Employee implements Serializable {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="EMPLOYEEID")
    private int id;

    // Rest of columns and getter and setters for all
}

<强> EmployeeSkillSetPK

package <your_package>;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

/**
 *
 */
@Entity
@Table(name="SKILLSET")
public class SkillSet implements Serializable {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="SKILLSETID")
    private int id;

    // Rest of columns and getter and setters for all
}

<强> EmployeeSkillSet

/**
 * 
 */
package <your_package>;

import java.io.Serializable;

import javax.persistence.Embeddable;

/**
 *
 */
@Embeddable
public class EmployeeSkillSetPK implements Serializable {

    @ManyToOne
    private Employee emp;

    @ManyToOne
    private SkillSet sk;
    /**
     * @return the employee
     */
    public Employee getEmployee() {
        return emp;
    }
    /**
     * @param employee the employee to set
     */
    public void setEmployee(Employee employee) {
        this.employee = employee;
    }
    /**
     * @return the sk
     */
    public SkillSet getSkillSet() {
        return sk;
    }
    /**
     * @param sk the sk to set
     */
    public void setSkillSet(SkillSet sk) {
        this.sk = sk;
    }

    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }

        if (o == null || getClass() != o.getClass()) {
            return false;
        }

        EmployeeSkillSetPK that = (EmployeeSkillSetPK) o;

        if (employee != null ? !employee.equals(that.employee) : that.employee != null) {
            return false;
        }
        if (sk != null ? !sk.equals(that.sk) : that.sk != null) {
            return false;
        }

        return true;
    }

    public int hashCode() {
        int result;
        result = (employee != null ? employee.hashCode() : 0);
        result = 31 * result + (sk != null ? sk.hashCode() : 0);
        return result;
    }
}

这是针对JPA 1.0的，我现在无法测试代码，但它应该可以正常工作。

请注意，我自己编写了表名和列名。根据需要调整它。

JPA：将ManyToMany关系映射到其他属性

2 个答案: