休眠物體映射

各位晚安，

我想對具有以下物體及其透視關系的資料庫進行建模：

但是每次我運行 Java 專案在資料庫中創建模型時，我創建的都是這樣的：

還有另一種映射這種關系的方法嗎？我是這樣映射的：

文章物體：

@Entity
public class Article {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false)
    private Boolean featured;

    @Column(nullable = false)
    private String title;

    @Column(nullable = false)
    private String url;

    @Column(name = "image_url", nullable = false)
    private String imageUrl;

    @Column(name = "news_site", nullable = false)
    private String newsSite;

    @Column(nullable = false)
    private String summary;

    @Column(name = "published_at", nullable = false)
    private String publishedAt;

    @OneToMany
    @JoinColumn(name = "launches_id")
    private List<Launches> launches;

    @OneToMany
    @JoinColumn(name = "events_id")
    private  List<Events> events;
}

啟動物體

@Entity
public class Launches {
    @Id
    private String id;

    private String provider;
}

事件物體：

@Entity
public class Events {
    @Id
    private Long id;

    private String provider;
}

我想用其他文章中出現的相同啟動器和事件來映射這個 JSON：

{
    "id": 4278,
    "title": "GAO warns of more JWST delays",
    "url": "https://spacenews.com/gao-warns-of-more-jwst-delays/",
    "imageUrl": "https://spacenews.com/wp-content/uploads/2019/08/jwst-assembled.jpg",
    "newsSite": "SpaceNews",
    "summary": "",
    "publishedAt": "2020-01-28T23:25:02.000Z",
    "updatedAt": "2021-05-18T13:46:00.284Z",
    "featured": false,
    "launches": [
        {
            "id": "d0fa4bb2-80ea-4808-af08-7785dde53bf6",
            "provider": "Launch Library 2"
        }
    ],
    "events": []
},
{
    "id": 4304,
    "title": "Government watchdog warns of another JWST launch delay",
    "url": "https://spaceflightnow.com/2020/01/30/government-watchdog-warns-of-another-jwst-launch-delay/",
    "imageUrl": "https://mk0spaceflightnoa02a.kinstacdn.com/wp-content/uploads/2020/01/48936479373_2d8a120c8e_k.jpg",
    "newsSite": "Spaceflight Now",
    "summary": "",
    "publishedAt": "2020-01-30T04:08:00.000Z",
    "updatedAt": "2021-05-18T13:46:01.640Z",
    "featured": false,
    "launches": [
        {
            "id": "d0fa4bb2-80ea-4808-af08-7785dde53bf6",
            "provider": "Launch Library 2"
        }
    ],
    "events": []
}

uj5u.com熱心網友回復：

根據您的圖表，它應該是：

    @ManyToOne
    @JoinColumn(name = "launches_id")
    private Launches launches;

    @ManyToOne
    @JoinColumn(name = "events_id")
    private  Events events;

...而不是@OneToMany;) （是否有一個“文章”（id=x）具有launchers_id=y 和launchers_id=z？不，反之亦然！:)

...對于@OneToMany，您應該找到“在另一邊”（關系）的連接列。

根據您的 JSON，它是 OneToMany. 但是，我們必須繪制/預期：

@Entity
class Article {
    //... id, columns, blah
    @OneToMany
    @JoinColumn(name = "article_id")  // Launches "owns the relationship"/column 
    private List<Launches> launches;

    @OneToMany
    @JoinColumn(name = "article_id")  // Events...!
    private  List<Events> events;
}

通常，（當您通過 json 公開資料庫模型時）確保：

• 沒有“圈子”（雙向關聯）。( @JsonManagedReference, @JsonBackReference, @JsonIgnoreProperties, ... )

• 不要公開您不想公開的資料。( @JsonIgnoreProperties, ...)

關于 Hibernate-ManyToOne，請參考https://vladmihalcea.com/the-best-way-to-map-a-onetomany-association-with-jpa-and-hibernate/

關于 彈簧資料-jpa，最好：

• gs-資料-jpa
• gs-資料休息
• spring-boot-ref，資料-jpa
• 參考檔案，資料-jpa
• 參考檔案，資料休息

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