Question

我目前正在重构我的项目以使用Room Persistence Library（顺便说一句，喜欢它），但是我遇到了一个问题，我在这个问题中查询我的数据库是否存在继承自实体类。超类中的字段由于某种原因没有从查询中加载数据。

继承我的班级（顺便说一下，这是一个自定义的课程，而不是真正的课程，因为我无法分享真正的源代码）：

Task.java：

public class Task extends SyncEntity {

    @PrimaryKey(autoGenerate = true)
    public final String taskId;

    public final String title;

     /** Status of the given task.
     * Enumerated Values: 0 (Active), 1 (Inactive), 2 (Completed)
     */
    @TypeConverters(StatusConverter.class)
    public final Status status;

    @TypeConverters(DateConverter.class)
    public Date startDate;

    public Examination(@NonNull String taskId,
                   @NonNull String title,
                   @NonNull Status status,
                   @NonNull Date startDate,
                   @NonNull Long createdAt,
                   @Nullable Long updatedAt,
                   @Nullable Boolean deleted) {
        super(createdAt, updatedAt, deleted);
        this.taskId = taskId;
        this.title = title;
        this.status = status;
    }

    @Ignore
    public Task(@NonNull Builder builder) {
        super(builder);
        this.taskId = builder.taskId;
        this.title = builder.title;
        this.status = builder.status;
    }

    ...
    ** left out for brevity **

}

和我的查询：

@Dao
public interface TaskRepository {

    @Query("SELECT " +
            "taskId, " +
            "title, " +
            "status, " +
            "startDate, " +
            "created_at AS createdAt, " +
            "updated_at AS updatedAt " +
            "FROM tasks " +
            "WHERE status = 0 " +
            "AND deleted = 0")
    LiveData<List<Task>> getActiveTasks();
    ...
    ** left out for brevity **
}

查询返回一个结果，其中createdAt为null，它不应该是，因为所有SyncEntities默认创建到System.currentTimeMillis（）并且我已经双重检查该值是否存在于数据库中。 / p>

编译时我也收到以下警告，但我不明白为什么：

警告：（33,33）查询返回一些列[createdAt，updatedAt] com.example.project.data.models.entities.Task不使用它们。您可以在字段上使用@ColumnInfo注释来指定映射。 com.example.project.data.models.entities.Task有一些字段[created_at，updated_at，deleted]，它们不会返回查询。如果不应该从结果中读取它们，则可以用@Ignore注释标记它们。您可以通过抑制此警告用方法注释方法 @SuppressWarnings（RoomWarnings.CURSOR_MISMATCH）。返回的列查询：taskId，title，status，startDate，createdAt，updatedAt。 com.example.project.data.models.entities.Task中的字段： created_at，updated_at，deleted，taskId，title，status，startDate。

这是我的超级班： SynEntity.java

@Entity
public class SyncEntity implements Syncable {

    @NonNull
    @ColumnInfo(name = "created_at")
    public final Long createdAt;

    @Nullable
    @ColumnInfo(name = "updated_at")
    public final Long updatedAt;

    @Nullable
    public final Boolean deleted;

    SyncEntity(@NonNull Long createdAt,
               @Nullable Long updatedAt,
               @Nullable Boolean deleted) {
            this.createdAt = createdAt;
            this.updatedAt = updatedAt;
            this.deleted = deleted == null ? false : deleted;
    }

    @Ignore
    SyncEntity(@NonNull Builder<?> builder) {
            this.createdAt = builder.createdAt;
            this.updatedAt = builder.updatedAt;
            this.deleted = builder.deleted;
    }

    public static class Builder<T extends Builder<T>> {

        @NonNull
        private Long createdAt = System.currentTimeMillis();
        @Nullable
        private Long updatedAt = null;
        @NonNull
        private Boolean deleted = false;

        public Builder() {}

    ...
    ** left out for brevity **

}

这是房间或预期行为中的错误吗？

Answer 1

修改正如@pskink在评论中指出的那样，问题就是查询。

问题在于查询：

@Override public LiveData<List<UserPet>> loadUserAndPetNames() { final String _sql = "SELECT users.firstName AS firstName, users.lastName AS lastName, pets.name AS petName, pets.created_at AS createdAt, pets.updated_at AS updatedAt, pets.deleted AS deleted FROM users, pets WHERE users.userId = pets.user_id"; final RoomSQLiteQuery _statement = RoomSQLiteQuery.acquire(_sql, 0);

查询将列名返回为“createdAt”，但实体的字段使用“created_at”显式注释，因此它们不匹配。

Android Room：Query在继承的字段中返回null

1 个答案: