[FIXED] Best practice of handling relations between tables in Spring Data R2dbc

Issue

I tried to create a user/roles relation in RDBMS and want to use R2dbc(Spring Data R2dbc) to shake hands with the backend database.

Assume there are three tables, users, roles, and user_roles.

@Table("users")
class User {
    @Id
    private String username;

    private String password;

    private String email;

    @Builder.Default
    private boolean active = true;

    @Builder.Default
    private List<String> roles = new ArrayList<>();

    @Column("created_at")
    private LocalDateTime createdDate;

}

Unlike JPA, R2dbc reuses the spring-data-relational-common(which is also used in Spring Data Jdbc) to annotate the tables, but there is no facility to resolve the relations, such as the roles here.

Solution

Spring Data R2DBC currently does not support relationships.

So what you would do is to have a separate entity User2Role with two properties: String username and String rolename referencing the ids of the referenced entities.

Since you also tagged the question Spring Data JDBC: Spring Data JDBC does support 1:1 and 1:M references, but not M:1 or M:N relationships. See https://spring.io/blog/2018/09/24/spring-data-jdbc-references-and-aggregates for some background on that.

Spring Data R2DBC might eventually move to the same model.

Answered By - Jens Schauder