标签: android-room-relation

如果我想关联 2 个表并且关系不仅是一列而是更多，有没有办法使用带有更多参数的 Room @Relation 注释来实现这一点？也许像下面这样

@Relation(parentColumn = "{message_id,account_id}", entityColumn = "{message_id, from_account_id}", entity = Message::class)
    var messageList: List<Message> = ArrayList()

所以连接有多个约束？

在我的 Android 应用程序中，我使用 Room 进行数据存储。我目前面临的问题是，我需要在嵌入对象的 @Relation 中放入 2 列，因为关系依赖于 2 列。结构见下图：

@Entity(tableName = "damages")
public class Damage {
    @PrimaryKey(autoGenerate = true)
    @NonNull
    private Long id;
    @NonNull
    private Long projectId;
    @NonNull
    private Long codeId;
    private String description;
    ...
}

@Entity(tableName = "damage_codes")
public class DamageCode {
    @PrimaryKey(autoGenerate = true)
    @NonNull
    private Long id;
    @NonNull
    private Long projectId;
    @NonNull
    private String name;
    private String description;
    @NonNull
    private String code;
    @NonNull
    private String damageType;
    ...
}

@Entity(tableName = "damage_types")
public class DamageType { …

我在 Room 数据库上设置了多对多关系，如下图所示：

我想向“CrossRef”表添加额外的字段。我的问题是如何让 DateWithSteaks 从“CrossRef”表中获取这个“isCompleted”变量？

@Entity
public class Steak{

    @PrimaryKey(autoGenerate = true)
    public int id;

    public String title;
}


@Entity
public class Date {
    @PrimaryKey
    public long date;

    public Date() {
        date = new LocalDate().toDate().getTime();
    }
}


@Entity(primaryKeys = {"date", "id"})
public class DateSteakCrossRef {
    public long date;
    public int id;
    public boolean isCompleted;
}


public class DateWithSteaks {
    @Embedded Date date;

    @Relation(
            parentColumn = "date",
            entityColumn = "id",
            associateBy = @Junction(DateSteakCrossRef.class)
    )

    public List<Steak> steaks;
}

我有 2 个实体，并且Grade有一个通往教室的外键。嵌入式实体看起来像这样，StudentStudentClassRoom

data class ClassRoom(

    @Embedded
    val level: ClassLevel

    @Relation(
        parentColumn = "id",
        entityColumn = "ClassLevel"
    )
    val students: List<Student>,

    // val strength: Int ?

)