Hibernate复合键,它是另一个表的foreigen键

Question

我有两个表Part和SubPart.部分表具有一般字段,如id,name,desc等.SubPart表具有part_id,sub_part_id作为复合键.这两列都引用了Part表,并且每个列都有一对多的映射,就像Part表中的每个part_id一样,SubPart表中的两个列都可以有多个条目.我在定义SubPart表的复合键时遇到问题.我尝试了嵌入式标签,但它不起作用.我该如何解决这个问题.非常感谢.

像这样的零件表.

@Entity
@Table(name="Part")
public class Part {

    @Id
    @GeneratedValue
    @Column(name="Part_Id")
    private int id;
    @Column(name="Part_Number")
    private String partNumber;
    @Column(name="Part_Name")
    private String partName;
}

子部件表

@Entity
@Table(name="SubPart")
public class SubPart {
    // part and subPart combination is the compound key here.
    @ManyToOne
    @JoinColumn(name="Part_Id")
    private Part part;

    @ManyToOne
    @JoinColumn(name="Sub_Part_Id")
    private Part subPart;

    @Column(name="Quantity")
    private Integer quantity;
}

Answer 1

你说

我在定义 SubPart表的复合键时遇到问题

当你有一个复合主键时,你必须定义一个类(通常是一个静态内部类)来定义你的复合素数键(只是一个建议:因为Hibernate使用代理,更喜欢把你的注释映射放在getter而不是field成员)

/**
  * When both entity class and target table SHARE the same name
  * You do not need @Table annotation
  */
@Entity
public class SubPart implements Serializable {

    @EmbeddedId
    private SubPartId subPartId;

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="PART_ID", insertable=false, updateable=false)
    private Part part;

    @ManyToOne(fetch=FetchType.LAZY)
    @JoinColumn(name="SUP_PART_ID", insertable=false, updateable=false)
    private SubPart subPart;

    /**
      * required no-arg constructor
      */
    public SubPart() {}
    public SubPart(SubPartId subPartId) {
        this.subPartId = subPartId;
    }

    // getter's and setter's

    /**
      * It MUST implements Serializable
      * It MUST overrides equals and hashCode method
      * It MUST has a no-arg constructor
      *
      * Hibernate/JPA 1.0 does not support automatic generation of compound primary key
      * You SHOULD set up manually
      */
    @Embeddable
    public static class SubPartId implements Serializable {

        @Column(name="PART_ID", updateable=false, nullable=false)
        private Integer partId;
        @Column(name="SUB_PART_ID", updateable=false, nullable=false)
        private Integer subPartId;

        /**
          * required no-arg constructor
          */
        public SubPartId() {}
        public SubPartId(Integer partId, Integer subPartId) {
            this.partId = partId;
            this.subPartId = subPartId;
        }

        // getter's and setter's

        @Override
        public boolean equals(Object o) {
            if(!(o instanceof SubPartId))
                return null;

            final SubPartId other = (SubPartId) o;
            return new EqualsBuilder().append(getPartId(), other.getPartId())
                                      .append(getSubPartId(), other.getSubPartId())
                                      .isEquals();
        }

        @Override
        public int hashCode() {
            return new HashCodeBuilder().append(getPartId())
                                        .append(getSubPartId())
                                        .toHashCode();  
        }

    }

}

注意Part和SubPart映射已标记为insertable = false, updateable = false因为映射已在复合主键中定义.除非标记为insertable = false,updateable = false,否则Hibernate 不允许您使用相同列映射两个属性.否则你会看到这个很好的例外

应标记为insertable = false,updateable = false