Room依赖
implementation "android.arch.persistence.room:runtime:1.0.0"
annotationProcessor "android.arch.persistence.room:compiler:1.0.0"
查找
- 查找表中所有数据
/**
* 查找user
* @return
*/
@Query("SELECT * FROM banners")
List<BannerModel> findBanners();
- 按条件查找
/**
* filters
* @return
* @param typeSort
*/
@Query("SELECT * FROM filters WHERE type != :typeSort")
List<FilterItemModel> findFilters(String typeSort);
- 限制条数的条件查找
/**
* 获取排序
* @return
*/
@Query("SELECT * FROM filters WHERE type = :name LIMIT 0,1")
FilterItemModel findSort(String name);
现在获取的是第一条数据
//文档中的例子
@Dao
public interface MyDao {
@Query("SELECT first_name, last_name FROM user WHERE region IN (:regions)")
public List<NameTuple> loadUsersFromRegions(List<String> regions);
}
在user表中查找满足集合List<String> regions中条件的元素
- 获取总行数
/**
* 获取数据库表中总条数
* @return
*/
@Query("SELECT count(*) FROM search_history")
long findHistoryCount();
- 获取某一列的和
/**
* 求和
* @return
*/
@Query("SELECT sum(count) FROM status_stock")
long findStatusStockCount();
- 按照降序排列(ASC升序 DESC降序)
/**
* 查找user
* @return
*/
@Query("SELECT * FROM search_history ORDER BY time DESC")
List<SearchHistoryModel> findSearchHistory();
文档中的例子:
@Dao
public interface MyDao {
//正常的查询
@Query("SELECT * FROM user WHERE age != :minAge")
public User[] loadAllUsersOlderThan(int minAge);
}
@Dao
public interface MyDao {
//区间中的值
@Query("SELECT * FROM user WHERE age BETWEEN :minAge AND :maxAge")
public User[] loadAllUsersBetweenAges(int minAge, int maxAge);
//或关系的查询
@Query("SELECT * FROM user WHERE first_name LIKE :search "
+ "OR last_name LIKE :search")
public List<User> findUserWithName(String search);
}
如果,你不想查到表 行中所有字段,则
1.定义一个实体
public class NameTuple {
@ColumnInfo(name="first_name")
public String firstName;
@ColumnInfo(name="last_name")
public String lastName;
}
2.查询
@Dao
public interface MyDao {
@Query("SELECT first_name, last_name FROM user")
public List<NameTuple> loadFullName();
}
- 多表查询Querying multiple tables
@Dao
public interface MyDao {
@Query("SELECT user.name AS userName, pet.name AS petName "
+ "FROM user, pet "
+ "WHERE user.id = pet.user_id")
public LiveData<List<UserPet>> loadUserAndPetNames();
// You can also define this class in a separate file, as long as you add the
// "public" access modifier.
//注意 public
static class UserPet {
public String userName;
public String petName;
}
}
更新
- 更新指定条目
/**
* 更新时间
* @param time
*/
@Query("UPDATE search_history SET time = :time WHERE content = :content")
void updateSearchHistory(String content,long time);
删除数据
- 删除所有数据
/**
* 删除表
* @return
*/
@Query("DELETE FROM filters")
void delectFilters();
- 删除最后一条
/**
* 删除最后一个
* @return
*/
@Query("DELETE FROM search_history WHERE time in(SELECT time FROM search_history ORDER BY time ASC LIMIT 1 )")
void delectLastHistory();
- 按条件删除
/**
* 删除表by listtype
* @return
*/
@Query("DELETE FROM vehicle_model WHERE listType = :type")
void delectVehicleByType(String type);
补充
1.List<String>这样的元素
private ArrayList<String> tags;
这样的元素,可以通过Converter搞定
/**
* If you have any questions, you can contact by email { wangzhumoo@gmail.com}
*
* @author 王诛魔 2017/12/27 上午11:51
*/
public class TagsConverter {
@TypeConverter
public static ArrayList<String> fromString(String value) {
Type listType = new TypeToken<ArrayList<String>>() {}.getType();
return new Gson().fromJson(value, listType);
}
@TypeConverter
public static String fromArrayList(ArrayList<String> list) {
Gson gson = new Gson();
String json = gson.toJson(list);
return json;
}
}
在db中,会存为
["精选"]
["精选","急售"]
["准新","SUV"]
3.@Embedded
作用是,把已经写好的普通的类添加到数据表中.
用Room的文档做说明:
//这是一个标准的数据表
@Entity
class User {
@PrimaryKey
public int id;
public String firstName;
}
其中只有id , firstName
而我想添加
street;
state;
city;
postCode;
刚好之前写了一个类叫Address
class Address {
public String street;
public String state;
public String city;
@Ignore
public String nothing;
@ColumnInfo(name = "post_code")
public int postCode;
}
那么我通过 @Embedded
@Entity
class User {
@PrimaryKey
public int id;
public String firstName;
@Embedded
public Address address;
}
表中就会有:
names: id, firstName, street, state, city, and post_code
如果你想给@Embedded的类中所有元素前面加上统一的标志
@Embedded(prefix = "address_")
表中就会有:
names: id, firstName, address_street, address_state, address_city, and address_post_code
3.List<Object>这样的数据
- 解决方法
google developer
真的给谷歌跪了,什么鬼文档
@Entity
public class User {
// 这里是用户的 Id
@PrimaryKey
public int id;
//省略
...
}
@Entity
public class Book {
//书的id
@PrimaryKey
public int bookId;
//这里就是这本书与 User的关系,这里的是User.id
public int userId;
public String name;
public String desc;
}
//注意,什么注解也不要加
public class UserAndBooks {
//加入所有的user的属性
@Embedded
public User user;
//这里定义User 和 Book的关系
@Relation(parentColumn = "id", entityColumn = "userId", entity = Book.class)
public List<Book> books;
}
//文档上还讲了一个比较牛逼的功能,这里不讨论
public class UserAndAllPets {
@Embedded
public User user;
@Relation(parentColumn = "id", entityColumn = "userId", entity = Book.class,
projection = {"name"})
public List<String> bookNames;
}
//然后,dao是这样的
@Dao
public interface UserDao {
@Query("SELECT * FROM User")
public List<UserAndBooks> loadUserWithBooks();
}
