android专题-数据库Room

Room介绍

room是Google官方推荐的ORM数据库框架，抽象出sqlite访问的数据库。
包含三大组件：

Entity 定义表结构，每个entity类对一个表，默认会把entity类所有字段都创建为表字段
Dao 定义entity类的CRUD(增删查改)功能
Database 数据库的访问入口，注解定义数据库的实体表，数据库版本控制，表结构导出、表结构修改等都在这里处理

步骤

1.添加依赖

 def room_version = '2.3.0-alpha04'implementation rootProject.ext.dependencies.room_runtimeannotationProcessor rootProject.ext.dependencies.room_compilerandroidTestImplementation rootProject.ext.dependencies.room_testing

2.定义Entity实体表

@Entity 注解并在@Database 注解中的 entities 属性所引用，Room就会在数据库中为这个被 @Entity 注解的类创建一张表
@PrimaryKey 每个entity至少要有一个主键(PrimaryKey),autoGenerate表示这个值自动生成
@Entity(primaryKeys = {“xxx”, “xxx”}) 如果是复合主键的话, 你需要使用注解@Entity的primaryKeys属性

@Entity(primaryKeys = {"firstName", "lastName"})
public class User {public String firstName;public String lastName;@IgnoreBitmap picture;
}

@ColumnInfo(name = “xxx”) 定义表字段，也可以不使用此注解，默认为所有属性生成表字段
@Ignore 如果Engity类中某个属性不想保存到数据库，可以使用@Ignore注解忽略

@Entity
public class User {@PrimaryKeypublic int id;public String firstName;public String lastName;@IgnoreBitmap picture;
}

@Entity(indices = {@Index(“name”), @Index(value = {“last_name”, “address”})}) 为了加速查询速度. 要给实体添加索引

@Entity(indices = {@Index("name"),@Index(value = {"last_name", "address"})})
public class User {@PrimaryKeypublic int id;public String firstName;public String address;@ColumnInfo(name = "last_name")public String lastName;@IgnoreBitmap picture;
}

@Entity(foreignKeys = @ForeignKey(entity = User.class,
parentColumns = “id”,
childColumns = “user_id”)) 设置外键

@Entity(foreignKeys = @ForeignKey(entity = User.class,parentColumns = "id",childColumns = "user_id"))
public class Book {@PrimaryKeypublic int bookId;public String title;@ColumnInfo(name = "user_id")public int userId;
}

@Embedded注解来表示一个对象

public class Address {public String street;public String state;public String city;@ColumnInfo(name = "post_code")public int postCode;
}
@Entity
public class User {@PrimaryKeypublic int id;public String firstName;@Embeddedpublic Address address;
}

demo:

package com.wrs.project.module.app.common.database.entity;
import androidx.room.Entity;
import androidx.room.PrimaryKey;
import androidx.annotation.NonNull;@Entity(tableName = "Article")
public class Article {@PrimaryKey(autoGenerate = true)private int id;private String author;private String title;private String content;private String token;private int comments;public String getAuthor() {return author;}public void setAuthor(String author) {this.author = author;}public String getTitle() {return title;}public void setTitle(String title) {this.title = title;}public String getContent() {return content;}public void setContent(String content) {this.content = content;}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getToken() {return token;}public void setToken(String token) {this.token = token;}public int getComments() {return comments;}public void setComments(int comments) {this.comments = comments;}
}

3. 定义DAO

简单查询

@Dao
public interface MyDao {@Insert(onConflict = OnConflictStrategy.REPLACE)public void insertUsers(User... users);@Insertpublic void insertBothUsers(User user1, User user2);@Insertpublic void insertUsersAndFriends(User user, List<User> friends);
}

嵌套查询

@Dao
public interface MyDao {@Query("SELECT * FROM book "+ "INNER JOIN loan ON loan.book_id = book.id "+ "INNER JOIN user ON user.id = loan.user_id "+ "WHERE user.name LIKE :userName")public List<Book> findBooksBorrowedByNameSync(String userName);
}

@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.static class UserPet {public String userName;public String petName;}
}

demo

package com.wrs.project.module.app.common.database.dao;import androidx.lifecycle.LiveData;
import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.OnConflictStrategy;
import androidx.room.Query;
import androidx.room.Update;import com.wrs.project.module.app.common.database.entity.Article;import java.util.List;@Dao
public interface ArticleDao {/*** 增* @param entities*/@Insertvoid insert(Article... entities);/*** 删* @param entities*/@Deletevoid delete(Article... entities);/*** 查* @param title*/@Query("SELECT * FROM Article WHERE title = :title")List<Article> findByTitle(String title);/*** 查* @param titles*/@Query("SELECT * FROM Article WHERE title IN (:titles)")List<Article> findInTitles(List<String> titles);/*** 改* @param entities*/@Updatevoid update(Article... entities);@Insert(onConflict = OnConflictStrategy.REPLACE)List<Long> insertAll(List<Article> entities);@Deletevoid delete(Article entity);@Query("DELETE FROM Article")void deleteAll();@Deletevoid deleteArticle(Article entity);@Query("SELECT * FROM Article")List<Article> findAll();@Query("SELECT * FROM Article")LiveData<List<Article>> loadSignList();
}

4. 定义Database

package com.wrs.project.module.app.common.database;import android.content.Context;import androidx.room.Room;
import androidx.room.RoomDatabase;
import androidx.room.TypeConverters;
import androidx.room.migration.Migration;
import androidx.sqlite.db.SupportSQLiteDatabase;import com.wrs.project.module.app.common.database.conversion.ConversionFactory;
import com.wrs.project.module.app.common.database.dao.ArticleDao;
import com.wrs.project.module.app.common.database.entity.Article;@androidx.room.Database(entities = { Article.class}, // 声明需要创建表的实体version = 2, // 数据库版本号exportSchema = true  // 表结构是否需要导出
)
@TypeConverters({ConversionFactory.class}) // 属性类型转换，这里值转换了Date类
public abstract class Database extends RoomDatabase {public abstract ArticleDao articleDao(); // 声明每个entity的dao类private static Database sInstance; // 创建访问数据库比较耗资源，生成单例方便访问public static Database getInstance(final Context context) {if (sInstance == null) {synchronized (Database.class) {if (sInstance == null) {sInstance = create(context.getApplicationContext());}}}return sInstance;}private static Database create(final Context context) {return Room.databaseBuilder(context,Database.class,"phonesign_db").addMigrations(MIGRATION_1_2) // 构建版本升级时表结构的变化.allowMainThreadQueries().build();}private static Migration MIGRATION_1_2 = new Migration(1,2) {@Overridepublic void migrate(SupportSQLiteDatabase database) {database.execSQL("ALTER TABLE Article "+ " ADD COLUMN token TEXT");database.execSQL("ALTER TABLE Article "+ " ADD COLUMN comments INTEGER NOT NULL DEFAULT 0");}};
}

5. 测试

package com.wrs.project.module.app.common;import android.content.Context;
import android.util.Log;import androidx.test.ext.junit.runners.AndroidJUnit4;
import androidx.test.platform.app.InstrumentationRegistry;import com.wrs.project.module.app.common.database.DBService;
import com.wrs.project.module.app.common.database.entity.Article;import org.junit.Test;
import org.junit.runner.RunWith;import java.util.ArrayList;
import java.util.Date;
import java.util.List;import static org.junit.Assert.assertEquals;@RunWith(AndroidJUnit4.class)
public class DatabaseInstrumentedTest {@Testpublic void useAppContext() {// Context of the app under test.Context appContext = InstrumentationRegistry.getInstrumentation().getTargetContext();AppMgr.context = appContext;AppMgr.debug = true;List<Article> list = new ArrayList<>();for (int i = 0; i < 6; i++) {Article entity = new Article();entity.setTitle("title" + i);entity.setDate(new Date());list.add(entity);}DBService.insertAll(list);List<Article> resultList = DBService.findAll();if (null != resultList && resultList.size() > 0) {for (int i = 0; i < resultList.size(); i++) {Article entity = resultList.get(i);Log.e("article", entity.getTitle());}}List<Article>  entityList = DBService.findByTitle("title5");Log.e("article", entityList.toString());}
}

项目源码：https://codechina.csdn.net/android1/projectbasic
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