1. 在Entity类中添加@ForeignKey约束，指定外键关系。
2. 在@Relation注解中指定父实体类和实体类的关联属性名。

示例代码：

@Entity(tableName = "orders", foreignKeys = {@ForeignKey(entity = Customer.class, parentColumns = "id", childColumns = "customer_id", onDelete = ForeignKey.CASCADE)}) public class Order { @PrimaryKey public long id;

@ColumnInfo(name = "customer_id")
public long customerId;

...

}

@Entity(tableName = "customers") public class Customer { @PrimaryKey public long id;

...

@Relation(parentColumn = "id", entityColumn = "customer_id", entity = Order.class)
public List orders;

}