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Android Room-处理对象中的对象列表和查询结果

android-room mysql android java

6

martinomburajr · 技术社区 · 8 年前

我正在使用Android的房间数据库,在理解如何:

当我添加 Person 向数据库中添加所有变量,例如。 List<Shoe> , List<Pet> 等等。
创建关系,以便在检索 人 ,检索其所有字段,例如 Pet, Shoe, Shirt 等等(不确定这是什么类型的查询)
执行简单查询,例如。 Retrieve Person where 鞋名称 = "boot" ;

我知道必须对对象列表使用外键关系,否则可以对单个对象使用 @Embed 或 @TypeConverter

示例代码如下所示;

@Entity(tableName = "person")
    public class Person {
        @PrimaryKey
        @NonNull
        private String personId;
        private List<Pet> pets;
        private List<Shoe> shoes;
        private List<Shirt> shirts;
    }

@Entity(foreignKeys = {
        @ForeignKey(
                entity = Person.class,
                parentColumns = "personId",
                childColumns = "personIdFk"
        )
    })
    public class Pet {
        String petId;
        String name;
        String personIdFk; //Foreign key to person
    }

@Entity(foreignKeys = {
            @ForeignKey(
                    entity = Person.class,
                    parentColumns = "personId",
                    childColumns = "personIdFk"
            )
    })
    public class Shoe {
        String shoeId;
        String name;
        String personIdFk; //Foreign key to person
    }


@Entity(foreignKeys = {
        @ForeignKey(
                entity = Person.class,
                parentColumns = "personId",
                childColumns = "personIdFk"
        )
    })
    public class Shirt {
            String shirtId;
            String name;
            String personIdFk; //Foreign key to person
        }

1 回复 | 直到 8 年前

1

14

Thorbear 8 年前

房间不直接支持此功能,因为 potential issues with lazy loading ,但使用一些刀的技巧是可能的。您需要显式地处理插入,并且要立即查询所有内容,您需要一个POJO来包装所有内容。

@Entity(foreignKeys = {
    @ForeignKey(
            entity = PersonEntity.class,
            parentColumns = "personId",
            childColumns = "personIdFk",
            onDelete = CASCADE
    )
})
public class Pet {
    @PrimaryKey
    private String petId;
    private String name;
    private String personIdFk;
}

@Entity(tableName = "person")
public class PersonEntity {
    @PrimaryKey
    private String personId;
}

public class Person {
    @Embedded
    private PersonEntity personEntity;
    @Relation(parentColumn = "personId", entityColumn = "personIdFk")
    private List<Pet> pets;
}

@Dao
public abstract class PersonDao {

    @Insert
    protected abstract void insert(PersonEntity personEntity);

    @Insert
    protected abstract void insert(List<Pet> pets);

    @Transaction
    public void insert(Person person) {
        insert(person.getEntity());
        insert(person.getPets());
    }

    @Query("SELECT * FROM person")
    public abstract List<Person> getAll();

}

@Database(entities = {PersonEntity.class, Pet.class}, version = 1)
public abstract class AppDatabase extends RoomDatabase {

    public abstract PersonDao personDao();

}

为简洁起见,省略了构造函数、getter和setter。