問題與MySQL自動生成的PK用於另一個表和JPA

Question

我的使用情況如下：我使用MySQL和JPA 2，我有兩個實體：訂購和的LineItem由一個一對多的關係相關。

我想爲GUI層在同一時間一起LineItem的持續訂單。

銘記秩序PK是自動生成的由MySQL和是LineItem的的PK的一部分，我不知道如何才能將其用於檢索生成的訂單PK LineItem PK在同一個事務中。

任何人都可以幫忙嗎？

而且您的反饋，這裏是從實體的一些示例代碼（我實際上是由用例/域之上。我的是更復雜的，所以你不會看到任何訂單或LineItem的）。

@Entity 
@Table(name = "advertisement") 
@Inheritance(strategy = InheritanceType.JOINED) 
@DiscriminatorColumn(name = "status_need_ID", discriminatorType = DiscriminatorType.INTEGER) 
@NamedQueries({ 
    @NamedQuery(name = "Advertisement.findAll", query = "SELECT a FROM Advertisement a"), 
    @NamedQuery(name = "Advertisement.findByAdvertisementID", query = "SELECT a FROM Advertisement a WHERE a.advertisementID = :advertisementID"), 
    @NamedQuery(name = "Advertisement.findByAdvertisementTitle", query = "SELECT a FROM Advertisement a WHERE a.advertisementTitle = :advertisementTitle"), 
    @NamedQuery(name = "Advertisement.findByAdvertisementCreationDate", query = "SELECT a FROM Advertisement a WHERE a.advertisementCreationDate = :advertisementCreationDate"), 
    @NamedQuery(name = "Advertisement.findByStatusneedID", query = "SELECT a FROM Advertisement a WHERE a.statusneedID = :statusneedID")}) 
public class Advertisement implements Serializable { 
    private static final long serialVersionUID = 1L; 
    @Id 
    @GeneratedValue(strategy = GenerationType.IDENTITY) 
    @Basic(optional = false) 
    @Column(name = "advertisement_ID", nullable = false) 
    private Integer advertisementID; 
    @Basic(optional = false) 
    @Column(name = "advertisement_title", nullable = false, length = 200) 
    private String advertisementTitle; 
    @Column(name = "advertisement_creation_date") 
    @Temporal(TemporalType.TIMESTAMP) 
    private Date advertisementCreationDate; 
    @Basic(optional = false) 
    @Lob 
    @Column(name = "advertisement_body", nullable = false, length = 2147483647) 
    private String advertisementBody; 
    @Column(name = "status_need_ID") 
    private Integer statusneedID; 
    @JoinTable(name = "postcode_to_advertisement_join", joinColumns = { 
     @JoinColumn(name = "advertisement_ID", referencedColumnName = "advertisement_ID", nullable = false)}, inverseJoinColumns = { 
     @JoinColumn(name = "postcode_ID", referencedColumnName = "postcode_ID", nullable = false)}) 
    @ManyToMany 
    private Collection<Postcode> postcodeCollection; 
    @JoinTable(name = "advertisement_to_duration_join", joinColumns = { 
     @JoinColumn(name = "advertisement_ID", referencedColumnName = "advertisement_ID", nullable = false)}, inverseJoinColumns = { 
     @JoinColumn(name = "duration_ID", referencedColumnName = "duration_ID", nullable = false)}) 
    @ManyToMany 
    private Collection<Duration> durationCollection; 
    @JoinTable(name = "full_or_part_time_basis_to_advertisement_join", joinColumns = { 
     @JoinColumn(name = "advertisement_ID", referencedColumnName = "advertisement_ID", nullable = false)}, inverseJoinColumns = { 
     @JoinColumn(name = "full_or_part_time_basis_ID", referencedColumnName = "full_or_part_time_basis_ID", nullable = false)}) 
    @ManyToMany 
    private Collection<FullOrPartTimeBasis> fullOrPartTimeBasisCollection; 
    @JoinTable(name = "advertisement_to_child_care_type_join", joinColumns = { 
     @JoinColumn(name = "advertisement_ID", referencedColumnName = "advertisement_ID", nullable = false)}, inverseJoinColumns = { 
     @JoinColumn(name = "child_care_type_ID", referencedColumnName = "child_care_type_ID", nullable = false)}) 
    @ManyToMany 
    private Collection<ChildCareType> childCareTypeCollection; 
    @JoinTable(name = "advertisement_to_school_holiday_join", joinColumns = { 
     @JoinColumn(name = "advertisement_ID", referencedColumnName = "advertisement_ID", nullable = false)}, inverseJoinColumns = { 
     @JoinColumn(name = "school_holiday_ID", referencedColumnName = "school_holiday_ID", nullable = false)}) 
    @ManyToMany 
    private Collection<SchoolHoliday> schoolHolidayCollection; 
    @JoinTable(name = "employment_contract_to_advertisement_join", joinColumns = { 
     @JoinColumn(name = "advertisement_ID", referencedColumnName = "advertisement_ID", nullable = false)}, inverseJoinColumns = { 
     @JoinColumn(name = "employment_contract_ID", referencedColumnName = "employment_contract_ID", nullable = false)}) 
    @ManyToMany 
    private Collection<EmploymentContract> employmentContractCollection; 
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "advertisement") 
    private Collection<AdvertisementToTimeSlotToDayJoin> advertisementToTimeSlotToDayJoinCollection; 
    @OneToMany(cascade = CascadeType.ALL, mappedBy = "advertisementID") 
    private Collection<Salary> salaryCollection; 
    @OneToOne(cascade = CascadeType.ALL, mappedBy = "advertisement") 
    private ParentToParentAdvertisement parentToParentAdvertisement; 
    @OneToOne(cascade = CascadeType.ALL, mappedBy = "advertisement") 
    private ParentToChildMinderAdvertisement parentToChildMinderAdvertisement; 
    @JoinColumn(name = "child_care_location_ID", referencedColumnName = "child_care_location_ID", nullable = false) 
    @ManyToOne(optional = false) 
    private ChildCareLocation childcarelocationID; 
    @JoinColumn(name = "account_ID", referencedColumnName = "account_ID", nullable = false) 
    @ManyToOne(optional = false) 
    private Account accountID; 



@Entity 
@Table(name = "advertisement_to_time_slot_to_day_join",schema="bignibou") 
@NamedQueries({ 
    @NamedQuery(name = "AdvertisementToTimeSlotToDayJoin.findAll", query = "SELECT a FROM AdvertisementToTimeSlotToDayJoin a"), 
    @NamedQuery(name = "AdvertisementToTimeSlotToDayJoin.findByDayID", query = "SELECT a FROM AdvertisementToTimeSlotToDayJoin a WHERE a.advertisementToTimeSlotToDayJoinPK.dayID = :dayID"), 
    @NamedQuery(name = "AdvertisementToTimeSlotToDayJoin.findByTimeslotID", query = "SELECT a FROM AdvertisementToTimeSlotToDayJoin a WHERE a.advertisementToTimeSlotToDayJoinPK.timeslotID = :timeslotID"), 
    @NamedQuery(name = "AdvertisementToTimeSlotToDayJoin.findByAdvertisementID", query = "SELECT a FROM AdvertisementToTimeSlotToDayJoin a WHERE a.advertisementToTimeSlotToDayJoinPK.advertisementID = :advertisementID")}) 
public class AdvertisementToTimeSlotToDayJoin implements Serializable { 
    private static final long serialVersionUID = 1L; 
    @EmbeddedId 
    protected AdvertisementToTimeSlotToDayJoinPK advertisementToTimeSlotToDayJoinPK; 
    @JoinColumn(name = "time_slot_ID", referencedColumnName = "time_slot_ID", nullable = false, insertable = false, updatable = false) 
    @ManyToOne(optional = false) 
    private TimeSlot timeSlot; 
    @JoinColumn(name = "day_ID", referencedColumnName = "day_ID", nullable = false, insertable = false, updatable = false) 
    @ManyToOne(optional = false) 
    private Day day; 
    @JoinColumn(name = "advertisement_ID", referencedColumnName = "advertisement_ID", nullable = false, insertable = false, updatable = false) 
    @ManyToOne(optional = false) 
    private Advertisement advertisement; 

Answer 1

這裏的基本想法，你將不得不在兩個階段保存你的實體。當然，你可以在同一個交易中完成。首先保存您的訂單，而不保存LineItem，然後檢索PK（如果訂單），然後將其設置爲LineItem（s），然後保存LineItem（s）。我想這是OneToMany註釋的CascadeType屬性，它會告訴JPA在兩個不同階段執行此操作，即在保存訂單時不保存LineItems。事情是這樣的：

@Entity 
public class Order { 
    @Id 
    @GeneratedValue(strategy=GenerationType.AUTO) 
    long id; 

    @OneToMany(cascade={}) 
    Set<LineItem> lineItems; 
} 

或保存訂單時，您已在設置了LineItem空，然後檢索PK，設置了LineItem，和了LineItem的PK，然後再保存訂單。

無視這部分的答案，如果你的數據庫設計是終局的，你不能改變它。

這是我個人的意見（基於多年的數據庫設計和維護）。因此，擺在首位，你有一個很好的理由中的LineItem採用複合PK而不是使用好，老surrogate primary key？

因爲如果你不這樣做，那麼你應該在LineItem的代理主鍵。否則，你會一直運行到的各種問題（例如，如果你碰巧有遷移數據）

編輯我的建議：

1. 在DB：使用AUTO_INCREMENT PK中你的表，因爲在這個例子中：http://dev.mysql.com/doc/refman/5.0/en/example-auto-increment.html
2. 在JPA映射：在這篇文章中去的第一個選項（自動）：http://www.objectdb.com/java/jpa/entity/generated