How can i mapping entities in spring boot jpa?

Question

I'm new in Spring Boot JPA

I have questions in JPA Entity mappings.

there is 4 tables in my MySql DB

SPACE, PROJECT, ISSUE, MEMBER

SPACE is Big Project which contains multiple PROJECT.

PROJECT contains multiple ISSUE.

and MEMBER can join only 1 SPACE and multiple PROJECT which MEMBER belongs to SPACE. MEMBER can write multiple ISSUE

in this situation, my ERD model is correct?

my ERD

and please check my jpa mappings. If there's anything wrong, please point it out.

    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;

I've been thinking about it for days, but I can't solve it because I lack knowledge. Please help me.

Answer 1

Assuming I got your situation right, you have A member that can have one Space and multiple project, space has multiple projects, every project can have more than one issue, every member can write more then one issue for each project.

Due to the suggestion the ERD you posted it's not corrected.

Here is the correct ERD

(I just wrote the Foreign Keys and Primary Keys, the rest its up to you)

And here you have all the entites:

Member

@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;
    }
}

Space

@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;
    }
}

Issue

@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;
    }
}

Project

@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;
    }


}

You don't have to put necessarily both @ManyToOne and @OneToMany annotation, the back-reference could be useful in some use case, you have to see if you need it or not. Remember the back reference could cause problems with deserialization, creating a stack overflow by circular reference. You can avoid this, using transient keyword or various annotation (depending on the library you are using, Jackson, Gson, ecc..).

Be careful to don't use FetchType.EAGER randomly here's the why => Difference between FetchType LAZY and EAGER in Java Persistence API?