要使用Android Room的onDelete cascade功能,需要遵循以下步骤:
@Entity(tableName = "parent_table")
public class ParentEntity {
@PrimaryKey
public int id;
// Other fields
// Define foreign key with onDelete cascade
@ForeignKey(entity = ParentEntity.class, parentColumns = "id", childColumns = "parent_id", onDelete = ForeignKey.CASCADE)
public int parent_id;
}
@Entity(tableName = "child_table")
public class ChildEntity {
@PrimaryKey
public int id;
// Other fields
// Define foreign key
public int parent_id;
}
@Dao
public interface MyDao {
@Insert
void insertParent(ParentEntity parentEntity);
@Insert
void insertChild(ChildEntity childEntity);
@Delete
void deleteParent(ParentEntity parentEntity);
@Delete
void deleteChild(ChildEntity childEntity);
}
现在,当你调用deleteParent方法删除父实体时,所有相关的子实体将被自动删除。
ParentEntity parent = new ParentEntity();
// Set parent fields
ChildEntity child1 = new ChildEntity();
// Set child1 fields
child1.parent_id = parent.id;
ChildEntity child2 = new ChildEntity();
// Set child2 fields
child2.parent_id = parent.id;
myDao.insertParent(parent);
myDao.insertChild(child1);
myDao.insertChild(child2);
myDao.deleteParent(parent); // This will also delete child1 and child2
这样,使用onDelete cascade功能时,当父实体被删除时,将会自动删除所有相关的子实体。