Implementing the Tweet domain model using JPA annotations will look like the following:

@Data
@NoArgsConstructor
@AllArgsConstructor
@Entity
public class Tweet {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer id;

    @CreationTimestamp
    private Timestamp postTime;

    @ManyToOne
    private User tweetUser;

    @NotNull
    private String content;

}

In the preceding code, @Entity is used to mark the Tweet class as a JPA entity. The @Id annotation marks the id property as the identity field of the document. The @Data annotation is from the Lombok library and is used to mark a POJO as a class that will hold data. This means that getters, setters, the equals method, the hashCode method, and the toString method will be generated for that class. @AllArgsConstructor, which will generate a constructor with all the properties, and @NoArgsConstructor, which will generate a default constructor.

Implementing the User domain model using JPA annotations will look like the following code:

@Data
@NoArgsConstructor
@AllArgsConstructor
@Entity
public class User {

    @Id
    @NotNull
    private String userId;

    @JsonIgnore
    @NotNull
    private String password;

    @NotNull
    @Column(unique = true)
    private String screenName;

    @NotNull
    private Role role;

    private String bio;

    private String profileImage;

    @ElementCollection
    private Set<String> following;

}

In the preceding code, @Entity is used to mark the Tweet class as a JPA entity. @AllArgsConstructor will generate a constructor with all the properties and @NoArgsConstructor will generate a default constructor. @ElementCollection is used to persist a Set collection.

Implementing the Role enum will look like the following code:

public enum Role {
    ADMIN, USER
}