我如何在 Spring Boot jpa 中映射实体？

Question

我是 Spring Boot JPA 的新手

我对 JPA 实体映射有疑问。

我的 MySql DB 中有 4 个表

空间、项目、问题、成员

SPACE 是包含多个 PROJECT 的大项目。

PROJECT 包含多个 ISSUE。

MEMBER 只能加入 1 个 SPACE 和 MEMBER 属于 SPACE 的多个 PROJECT。 MEMBER可以写多个ISSUE

在这种情况下，我的 ERD 模型是否正确？

my ERD

请检查我的 jpa 映射。 如有不妥，请指出。

    SPACE

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "space_no")
    private Long spaceNo;

    @NotEmpty
    @Column(name = "space_name", unique=true, length = 100)
    private String spaceName;

    /** 1:N relation */
    @OneToMany(mappedBy = "smsSpace")
    private List<PmsProject> pmsProjects = new ArrayList<>();

    PROJECT
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "project_no")
    private Long projectNo;

    @Column(name ="space_no")
    private Long spaceNo;

    @Column(name = "project_name", length = 100)
    private String projectName;

    /** 1:N relation */
    @OneToMany(mappedBy = "pmsProject")
    private List<ImsIssue> imsIssues = new ArrayList<>();

    @OneToMany(mappedBy = "pmsProject")
    private List<PmsProjectMember> projectMembers = new ArrayList<>();

    /** N:1 relation */
    @ManyToOne
    @JoinColumn(name = "space_no", referencedColumnName = "space_no", insertable = false, updatable = false)
    private SmsSpace smsSpace;

MEMBER

  @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "member_no")
    private Long memberNo;

    @Column(name = "mail_address", unique=true, length = 100)
    private String mailAddress;

    @Column(name = "name", length = 100)
    private String name;

    @Column(name = "keyword", length = 1000)
    private String keyword;

    @Column(name = "image", length = 1000)
    private String image;

    @Column(name = "password", length = 1000)
    private String password;

    @Column(name = "user_id", length = 50)
    private String userId;

    @Enumerated(EnumType.STRING)
    private MemberRole role;

    public void encodingPassword(String password) {
        this.password = password;
    }

    /** 1:N realtion */
    @OneToMany(mappedBy = "mmsMember")
    private List<PmsProjectMember> projectMembers = new ArrayList<>();

ISSUE
 @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "issue_no")
    private Long issueNo;

    @Column(name ="project_no")
    private Long projectNo;

    @Column(name = "issue_name", length = 1000)
    private String issueName;

    @Column(name = "priority")
    private Long priority;

    @Column(name = "status", length = 20)
    private String status;

    @Column(name = "summary", length = 100)
    private String summary;

    @Column(name = "is_overdue")
    private Long isOverdue;

    @Column(name = "issue_type_cd")
    private String issueTypeCd;

    /** N:1 relation */
    @ManyToOne
    @JoinColumn(name = "project_no", referencedColumnName = "project_no", insertable = false, updatable = false)
    private PmsProject pmsProject;

PROJECTMEMBER

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "group_no")
private Long groupNo;

@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "member_no")
private MmsMember mmsMember;

@ManyToOne(fetch = FetchType.EAGER)
@JoinColumn(name = "project_no")
private PmsProject pmsProject;

我已经想了好几天了，但由于我缺乏知识，我无法解决它。请帮帮我。

Answer 1

假设我的情况是正确的，你有一个成员可以有一个空间和多个项目，空间有多个项目，每个项目可以有多个问题，每个成员可以为每个项目编写多个问题。

由于建议，您发布的 ERD 未更正。

这是正确的 ERD

（我只是写了外键和主键，其余的由你决定）

这里有所有的实体：

会员

@Entity
@Table(name = "MEMBERS")
public class Member {

    //members is the property name in Project entity.
    @ManyToMany(mappedBy = "members")
    Set<Project> projects;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY, generator = "native")
    @Column(name = "MEMBER_ID")
    private Long id;
    @ManyToOne
    @JoinColumn(name = "SPACE_ID")
    private Space space;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Space getSpace() {
        return space;
    }

    public void setSpace(Space space) {
        this.space = space;
    }

    public Set<Project> getProjects() {
        return projects;
    }

    public void setProjects(Set<Project> projects) {
        this.projects = projects;
    }
}

空格

@Entity
@Table(name = "SPACES")
public class Space {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY, generator = "native")
    @Column(name = "SPACE_ID")
    private Long id;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }
}

问题

@Entity
@Table(name = "ISSUES")
public class Issue {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY, generator = "native")
    @Column(name = "ISSUE_ID")
    private Long id;

    @ManyToOne
    @JoinColumn(name = "MEMBER_ID")
    private Member member;


    @ManyToOne
    @JoinColumn(name = "PROJECt_ID")
    private Project project;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Member getMember() {
        return member;
    }

    public void setMember(Member member) {
        this.member = member;
    }

    public Project getProject() {
        return project;
    }

    public void setProject(Project project) {
        this.project = project;
    }
}

项目

@Entity
@Table(name = "PROJECTS")
public class Project {
    @ManyToMany
    @JoinTable(
            name = "PROJECTS_MEMBERS",
            joinColumns = @JoinColumn(name = "PROJECT_ID"),
            inverseJoinColumns = @JoinColumn(name = "MEMBER_ID"))//Is referring to the id of the other Entity, in this case, members
    Set<Member> members;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY, generator = "native")
    @Column(name = "PROJECT_ID")
    private Long id;
    @ManyToOne
    @JoinColumn(name = "SPACE_ID")
    private Space space;

    public Set<Member> getMembers() {
        return members;
    }

    public void setMembers(Set<Member> members) {
        this.members = members;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Space getSpace() {
        return space;
    }

    public void setSpace(Space space) {
        this.space = space;
    }


}

您不必同时添加 @ManyToOne 和 @OneToMany 注释，反向引用在某些用例中可能很有用，您必须看看是否需要它。请记住，反向引用可能会导致反序列化问题，通过循环引用创建堆栈溢出。您可以使用瞬态 keyword 或各种注释（取决于您使用的库，Jackson、Gson、ecc..）来避免这种情况。

注意不要随意使用 FetchType.EAGER 这就是为什么 => Difference between FetchType LAZY and EAGER in Java Persistence API?