java - Android 房间持久化库 : What is the best way to implement a many to many relation?

Question

我曾经使用 Realm，目前正在测试 Room 以比较这两种工具。

我正在尝试实现以下多对多关系:



这是我的Entity类:
Person :

@Entity(tableName = "person")
public final class RoomPerson {

  @PrimaryKey
  public int id;

  public String name;

}

Cat类(class) :

@Entity(tableName = "cat")
public final class RoomCat {

  @PrimaryKey
  public int id;

  public int age;

  public String name;

}

和 PersonCat类(class) :

@Entity(tableName = "person_cat", primaryKeys = { "personId", "catId" },
    indices = { @Index(value = { "catId" }) },
    foreignKeys = { @ForeignKey(entity = RoomPerson.class, parentColumns = "id", childColumns = "personId"),
        @ForeignKey(entity = RoomCat.class, parentColumns = "id", childColumns = "catId") })
public final class RoomPersonCat {

  public int personId;

  public int catId;

  public RoomPersonCat(int personId, int catId)  {
    this.personId = personId;
    this.catId = catId;
  }

}

我还有一个 POJO，以便将一个有猫的人操纵到我的应用程序中:

public final class RoomPersonWithAnimals {

  @Embedded
  public RoomPerson person;

  @Relation(parentColumn = "id", entityColumn = "id", entity = RoomCat.class)
  public List<RoomCat> cats;

}

问题是:如何保存List<RoomPersonWithAnimals> ?

我应该每次做 3 个请求以保存:

人入 table Person

猫进 table Cat

它的猫进 table PersonCat

这里是说明 3 个请求的 java 代码:

for (RoomPersonWithAnimals personWithAnimals : persons) {
  myRoomDatabase.roomPersonDao().insert(personWithAnimals.person);
  myRoomDatabase.roomCatDao().insertAll(personWithAnimals.cats.toArray(new RoomCat[personWithAnimals.cats.size()]));

  for (RoomCat cat : personWithAnimals.cats) {
    myRoomDatabase.roomPersonCatDao().insert(new RoomPersonCat(personWithAnimals.person.id, cat.id));
  }
}

在 Realm 中，可以只在一个请求中保存这些数据。是房间的限制还是我的实现有误？

预先感谢您的帮助 !

Answer 1

从 Room 2.2 开始，ORM 支持表之间所有可能的关系。
见媒体专文:Database relations with Room