Android Room Annotation使用简介

2017-08-17 本文已影响670人 tianbin

本文主要记录了Room Persistence Library中注解的使用方法。代码已上传到Github，欢迎star，fork

架构示意图

如下图

添加依赖

compile "android.arch.persistence.room:runtime:1.0.0-alpha5"
annotationProcessor "android.arch.persistence.room:compiler:1.0.0-alpha5"

准备工作

Create Model

@Entity
public class Library {

    @PrimaryKey(autoGenerate = true)
    public int id;
    @ColumnInfo(name = "library_name")
    public String name;
    
    @Embedded
    public Address address;
}

public clas Address {

    public String city;
    public String street;

    @ColumnInfo(name = "post_code")
    public int postCode;
}

Create Dao

@Dao
public interface LibraryDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insert(Library library);
}

Create Database

@Database(entities = {Library.class}, version = 1)
public abstract class LibraryDatabase extends RoomDatabase {

    public abstract LibraryDao libraryDao();
}

Init Database

public class RoomApplication extends Application {

    private LibraryDatabase mLibraryDatabase;

    @Override
    public void onCreate() {
        super.onCreate();
      
        mLibraryDatabase = Room.databaseBuilder(getApplicationContext(),
                LibraryDatabase.class, "library").build();

        new Thread() {
            @Override
            public void run() {
                super.run();

                final Library library = new Library();
                library.name = "library 1";
               final Address address = new Address();
                address.city = "beijing";
                address.street = "shang di dong lu";
                address.postCode = 11111;
                library.address = address;
                mLibraryDatabase.libraryDao().insert(library);
            }
        }.start();
    }
}

结果为下图：

表中出现的两个id，其中一个是Room自动添加的，以下是Room生成的建表语句

_db.execSQL("CREATE TABLE IF NOT EXISTS `Library` (`id` INTEGER, `library_name` TEXT,`address` TEXT, PRIMARY KEY(`id`))");

Annotations的使用

Entity

@Entity

使用注解之外的另一种定义主键的方式

@Entity(primaryKeys = {"firstName", "lastName"})
为列添加索引

@Entity(indices = {@Index("name"),@Index(value = {"last_name", "address"})})

定义外键

@Entity(foreignKeys = @ForeignKey(entity = User.class,
                                  parentColumns = "id",
                                  childColumns = "user_id",
                                  onDelete = CASCADE))

自定义表名，默认使用类名为表名

@Entity(tableName = "users")

@PrimaryKey

@PrimaryKey(autoGenerate = true)

定义主键，并设置是否自动增长

@ColumnInfo

@ColumnInfo(name = "library_name")

自定义数据库表结构中该字段的列名

@Ignore

用来标记不需要持久化的字段

@Embedded

用来处理model嵌套的情况，如Library 中包含 Address

@ForeignKey

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

Dao

@Dao

标注Entity对应的Dao类（接口），Room会为它生成实现类

@Insert

@Insert(OnConflict=REPLACE)

被标注的方法只能返回 void，long，Long，long[]，Long[]或者List<Long>

@Update

被标注的方法只能返回void，int

@Delete

被标注的方法只能返回void，int

@Query

@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

@Dao
public interface LibraryDao {

    @Query("SELECT * FROM library")
    List<Library> query();
}

带参数查询

@Dao
public interface LibraryDao {

    @Query("SELECT * FROM library WHERE library_name = :name")
    Library query(String name);
}

只返回某些列

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();
}

带一组参数

@Dao
public interface LibraryDao {

    @Query("SELECT * FROM library WHERE city IN (:cityList)")
    List<Library> queryByCityName(List<String> cityList);
}

返回LiveData形式的结果

@Dao
public interface LibraryDao {

    @Query("SELECT * FROM library")
    LiveData<List<Library>> queryReturnLiveData();
}

返回Flowable形式的结果

@Dao
public interface LibraryDao {

    @Query("SELECT * FROM library")
    Flowable<List<Library>> queryReturnFlowable();
}

返回Cursor（不推荐）

@Dao
public interface LibraryDao {

    @Query("SELECT * FROM library")
    Cursor queryReturnCursor();
}

多表查询

@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);
}

Database

@Database

@Database(entities = {User.java}, version = 1)

定义数据库中包含的表，数据库版本

@TypeConverter

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.

POJO

@Relation

用于多表联查，Room会将查询结果中的数据对应到Pojo实例。

@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;
    }
}

以上Dao类中的方法都提供了测试方法，见Github

后续

数据库版本升级及迁移
RxJava & Room
Room源码分析