Building database with Room Persistence Library and test
[TOC]
- 使用注解之外的另一种定义主键的方式
// java
@Entity(primaryKeys = {"firstName", "lastName"})
// kotlin
@Entity(primaryKeys = arrayOf("firstName", "lastName"))- 为列添加索引
// java
@Entity(indices = {@Index("name"),@Index(value = {"last_name", "address"})})
// kotlin
@Entity(indices = arrayOf(
Index(value = "library_id", unique = true)
)
)- 定义外键
// java
@Entity(foreignKeys = @ForeignKey(entity = Library.class,
parentColumns = "id",
childColumns = "library_id",
onDelete = CASCADE))
// kotlin
@Entity(foreignKeys = arrayOf(
ForeignKey(entity = Library::class, parentColumns = arrayOf("id"),
childColumns = arrayOf("library_id"), onDelete = CASCADE)
))- 自定义表名，默认使用类名为表名
// java
@Entity(tableName = "users")
// kotlin
@Entity(tableName = "users")- 定义主键，并设置是否自动增长
// java
@PrimaryKey(autoGenerate = true)
// kotlin
@PrimaryKey(autoGenerate = true)- 自定义数据库表结构中该字段的列名
// java
@ColumnInfo(name = "library_name")
// kotlin
@ColumnInfo(name = "library_name")- 用来标记不需要持久化的字段
- 用来处理model嵌套的情况，如Library 中包含 Address
- 为model添加外键，建立对象之间的所属关系，也可以通过
@Relation来实现添加onDelete = CASCADE可以在进行级联删除，简单讲就是，如果删除了某条library数据，那么与之关联的category数据和与category数据关联的book数据，都会被删除
- 标注Entity对应的Dao类（接口），Room会为它生成实现类
- 被标注的方法只能返回
void，long，Long，long[]，Long[]或者List<Long>
@Insert(OnConflict=REPLACE)- 被标注的方法只能返回
void，int
- 被标注的方法只能返回
void，int
@Query注解是DAO类中最主要的注解，被用来执行数据库的读写操作。每一个被标注的方法都会在编译时被检查，如果查询方法存在语法错误或者数据库不存在该表，Room会给出对应的编译错误。
- 简单查询
// java
@Dao
public interface LibraryDao {
@Query("SELECT * FROM library")
List<Library> query();
}
// kotlin
@Dao
interface LibraryDao {
@Query("SELECT * FROM library")
fun query() : List<Library>
}- 带参数查询
// java
@Dao
public interface LibraryDao {
@Query("SELECT * FROM library WHERE library_name = :name")
Library query(String name);
}
// kotlin
@Dao
interface LibraryDao {
@Query("SELECT * FROM library WHERE library_name = :name")
fun query(name: String) : Library
}- 只返回某些列
// java
public class LibraryAddressName {
@ColumnInfo(name = "library_name")
public String libraryName;
@ColumnInfo(name = "city")
public String city;
}
@Dao
public interface LibraryDao {
@Query("SELECT library_name,city FROM library")
List<LibraryAddressName> queryLibraryAddressName();
}
// kotlin
class LibraryAddressName {
@ColumnInfo(name = "library_name")
var libraryName: String
@ColumnInfo(name = "city")
var city: String
}
@Dao
interface LibraryDao {
@Query("SELECT library_name,city FROM library")
fun queryLibraryAddressName() : List<LibraryAddressName>
}- 带一组参数
// java
@Dao
public interface LibraryDao {
@Query("SELECT * FROM library WHERE city IN (:cityList)")
List<Library> queryByCityName(List<String> cityList);
}
// kotlin
@Dao
interface LibraryDao {
@Query("SELECT * FROM library WHERE city IN (:cityList)")
fun queryByCityName(cityList: List<String>) : List<Library>
}- 返回LiveData形式的结果
// java
@Dao
public interface LibraryDao {
@Query("SELECT * FROM library")
LiveData<List<Library>> queryReturnLiveData();
}
// kotlin
interface LibraryDao {
@Query("SELECT * FROM library")
fun queryReturnLiveData() : LiveData<List<Library>>
}- 返回Flowable形式的结果
// java
@Dao
public interface LibraryDao {
@Query("SELECT * FROM library")
Flowable<List<Library>> queryReturnFlowable();
}
// kotin
@Dao
interface LibraryDao {
@Query("SELECT * FROM library")
fun queryReturnFlowable() : Flowable<List<Library>>
}- 返回Cursor（不推荐）
// java
@Dao
public interface LibraryDao {
@Query("SELECT * FROM library")
Cursor queryReturnCursor();
}
// kotlin
@Dao
interface LibraryDao {
@Query("SELECT * FROM library")
fun queryReturnCursor() : Cursor
}- 多表查询
// java
@Dao
public interface LibraryDao {
@Query("SELECT * FROM library "
+ "INNER JOIN category ON category.library_id = library.id "
+ "INNER JOIN book ON book.category_id = category.id "
+ "WHERE book.name LIKE :bookName")
Library findLibraryByBookName(String bookName);
}
// kotlin
interface LibraryDao {
@Query("SELECT * FROM library "
+ "INNER JOIN category ON category.library_id = library.id "
+ "INNER JOIN book ON book.category_id = category.id "
+ "WHERE book.name LIKE :bookName")
fun findLibraryByBookName(bookName: String) : Library
}- 定义数据库中包含的表，数据库版本
// java
@Database(entities = {User.java}, version = 1)
// kotlin
@Database(entities = arrayOf(User::class, Repo::class, Category::class, Library::class),
version = 1,
exportSchema = false)将Entity中字段类型进行转换后再持久化，可以选择范围，文档说明如下：
- If you put it on a Database, all Daos and Entities in that database will be able to use it.
- If you put it on a Dao, all methods in the Dao will be able to use it.
- If you put it on an Entity, all fields of the Entity will be able to use it.
- If you put it on a POJO, all fields of the POJO will be able to use it.
- If you put it on an Entity field, only that field will be able to use it.
- If you put it on a Dao method, all parameters of the method will be able to use it.
- If you put it on a Dao method parameter, just that field will be able to use it.
用于多表联查，Room会将查询结果中的数据对应到Pojo实例。
// java
@Dao
public interface LibraryDao {
@Query("SELECT * FROM library")
List<LibraryCategoryBook> queryByRelation();
}
public class LibraryCategoryBook {
@Embedded
public Library library;
@Relation(parentColumn = "id", entityColumn = "library_id", entity = Category.class)
public List<CategoryBook> categoryList;
public static class CategoryBook {
@Embedded
public Category category;
@Relation(parentColumn = "id", entityColumn = "category_id")
public List<Book> bookList;
}
}
// kotlin
@Dao
interface UserWithReposDao {
@Query("SELECT * from user")
fun getUsersWithRepos(): List<UserWithRepos>
}
class UserWithRepos(
@Embedded var user: User,
@Relation(parentColumn = "id", entityColumn = "userId")
var repoList: List<Repo>
) {
constructor() : this(User(), emptyList())
}