房间每次只插入 1 行（替换以前的）

Question

我已经设置了一些 FK 约束，它们很可能是罪魁祸首，但经过大量试验和错误后我无法弄清楚。

问题：每次我插入一所新大学时，它都会替换上一所。每次我在大学里插入一个学期，它就会取代旧的。每次我在学期中插入一门课程时，它都会取代旧的。

类如下：

User.class

@Entity
public class User
{
    @PrimaryKey
    @NotNull
    private String userEmail;
    private String userName;

    public User(String userName, String userEmail)
    {
        this.userName = userName;
        this.userEmail = userEmail;
    }
}

University.class

@Entity(foreignKeys = @ForeignKey(entity = User.class, parentColumns = "userEmail", childColumns = "userEmail", onDelete = CASCADE, onUpdate = CASCADE),
        indices = {@Index(value = {"userEmail"}, unique = true)})
public class University
{
    @PrimaryKey
    @NotNull
    private String universityName;
    private String userEmail;

    public University(String universityName, String userEmail)
    {
        this.universityName = universityName;
        this.userEmail = userEmail;
    }
}

Semester.class

@Entity(foreignKeys = @ForeignKey(entity = University.class, parentColumns = "universityName", childColumns = "universityName", onDelete = CASCADE, onUpdate = CASCADE),
        indices = {@Index(value = {"universityName"}, unique = true)})
public class Semester
{
    @PrimaryKey(autoGenerate = true)
    private Long semesterId;
    private String name;
    private String universityName;

    public Semester(Long semesterId, String name, String universityName)
    {
        this.semesterId = semesterId;
        this.name = name;
        this.universityName = universityName;
    }

    @Ignore
    public Semester(String name, String universityName)
    {
        this.name = name;
        this.universityName = universityName;
    }
}

Course.class

@Entity(foreignKeys = @ForeignKey(entity = Semester.class, parentColumns = "semesterId", childColumns = "semesterId", onDelete = CASCADE, onUpdate = CASCADE),
        indices = {@Index(value = {"semesterId"}, unique = true)})
public class Course
{
    @PrimaryKey(autoGenerate = true)
    private Long courseId;
    private String name;
    private String code;
    private Long semesterId;

    public Course(Long courseId, String name, String code, Long semesterId)
    {
        this.courseId = courseId;
        this.name = name;
        this.code = code;
        this.semesterId = semesterId;
    }

    @Ignore
    public Course(String name, String code, Long semesterId)
    {
        this.name = name;
        this.code = code;
        this.semesterId = semesterId;
    }
}

DAO

@Dao
public interface UserDao
{
    @Query("SELECT * FROM User LIMIT 1")
    User getUser();

    @Query("SELECT * FROM University WHERE userEmail = :userEmail")
    List<University> getUniversitiesByUser(String userEmail);

    @Query("SELECT * FROM University WHERE universityName = :universityName LIMIT 1")
    University getUniversityByName(String universityName);

    @Query("SELECT * FROM Semester WHERE name = :semesterName AND universityName = :universityName LIMIT 1")
    Semester getSemesterByNameAndUniversity(String semesterName, String universityName);

    @Query("SELECT * FROM Semester WHERE universityName = :universityName")
    List<Semester> getSemestersByUniversity(String universityName);

    @Query("SELECT * FROM Course WHERE semesterId = :semesterId")
    List<Course> getCoursesBySemester(long semesterId);

    /**
     * @param userEmail - The Email of the selected user
     * @return - A list of all incidents submitted by the user
     */
    @Query("SELECT * FROM Incident WHERE submitterEmail = :userEmail")
    List<Incident> getAllIncidentsByUser(String userEmail);

    // Updates
    @Update(onConflict = REPLACE) void updateUser(User user);
    @Update(onConflict = REPLACE) void updateUniversity(University university);
    @Update(onConflict = REPLACE) void updateSemester(Semester semester);

    // Inserts
    @Insert(onConflict = REPLACE) void insertUser(User user);
    @Insert(onConflict = REPLACE) void insertUniversity(University university);
    @Insert(onConflict = REPLACE) void insertSemester(Semester semester);
    @Insert(onConflict = REPLACE) void insertCourse(Course course);

    // Deletes
    @Delete void deleteUser(User user);
    @Delete void deleteUniversity(University university);
    @Delete void deleteSemester(Semester semester);
    @Query("DELETE FROM User")
    void deleteAllUsers();
}

Answer 1

通过在与 parent 的关系上使用唯一索引，您将 child 限制为 1-1 关系。

因此每学期只能有 1 门课程，每所大学只能有 1 个学期，每个用户邮箱只能有 1 所大学。

从索引中删除所有 unique = true。

您也只能按名称拥有 1 所大学，因为名称是主键，因此一所大学只能有 1 位用户。我建议不要让用户作为大学的 parent。

要允许一个用户就读一所大学，而让多个用户就读同一所大学，您可以颠倒这种关系。

然而，您可能希望用户上多所大学，在这种情况下，您可以使用中级（associative/reference/mapping 加上其他名称）table。

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