Room介紹

room是Google官方推薦的ORM數(shù)據(jù)庫框架，抽象出sqlite訪問的數(shù)據(jù)庫弧关。
包含三大組件：

• Entity 定義 表結(jié)構(gòu)，每個(gè)entity類對(duì)一個(gè)表世囊，默認(rèn)會(huì)把entity類所有字段都創(chuàng)建為表字段
• Dao 定義entity類的CRUD(增刪查改)功能
• Database 數(shù)據(jù)庫的訪問入口窿祥，注解定義數(shù)據(jù)庫的實(shí)體表，數(shù)據(jù)庫版本控制晒衩，表結(jié)構(gòu)導(dǎo)出、表結(jié)構(gòu)修改等都在這里處理

步驟

1.添加依賴

 def room_version = '2.3.0-alpha04'

 implementation rootProject.ext.dependencies.room_runtime
 annotationProcessor rootProject.ext.dependencies.room_compiler
 androidTestImplementation rootProject.ext.dependencies.room_testing

2.定義Entity實(shí)體表

@Entity 注解并在@Database 注解中的 entities 屬性所引用听系，Room就會(huì)在數(shù)據(jù)庫中為這個(gè)被 @Entity 注解的類創(chuàng)建一張表
@PrimaryKey 每個(gè)entity至少要有一個(gè)主鍵(PrimaryKey),autoGenerate表示這個(gè)值自動(dòng)生成
@Entity(primaryKeys = {"xxx", "xxx"}) 如果是復(fù)合主鍵的話, 你需要使用注解@Entity的primaryKeys屬性

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

    @Ignore
    Bitmap picture;
}

@ColumnInfo(name = "xxx") 定義表字段，也可以不使用此注解弃秆，默認(rèn)為所有屬性生成表字段
@Ignore 如果Engity類中某個(gè)屬性不想保存到數(shù)據(jù)庫髓帽，可以使用@Ignore注解忽略

@Entity
public class User {
    @PrimaryKey
    public int id;
    public String firstName;
    public String lastName;
    @Ignore
    Bitmap picture;
}

@Entity(indices = {@Index("name"), @Index(value = {"last_name", "address"})}) 為了加速查詢速度. 要給實(shí)體添加索引

@Entity(indices = {@Index("name"),
        @Index(value = {"last_name", "address"})})
public class User {
    @PrimaryKey
    public int id;
    public String firstName;
    public String address;

    @ColumnInfo(name = "last_name")
    public String lastName;

    @Ignore
    Bitmap picture;
}

@Entity(foreignKeys = @ForeignKey(entity = User.class,
parentColumns = "id",
childColumns = "user_id")) 設(shè)置外鍵

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

@Embedded注解來表示一個(gè)對(duì)象

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

    public String firstName;

    @Embedded
    public 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. 定義DAO

簡單查詢

@Dao
public interface MyDao {
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    public void insertUsers(User... users);

    @Insert
    public void insertBothUsers(User user1, User user2);

    @Insert
    public void insertUsersAndFriends(User user, List<User> friends);
}

嵌套查詢

@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
     */
    @Insert
    void insert(Article... entities);

    /**
     * 刪
     * @param entities
     */
    @Delete
    void 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
     */
    @Update
    void update(Article... entities);

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    List<Long> insertAll(List<Article> entities);

    @Delete
    void delete(Article entity);

    @Query("DELETE FROM Article")
    void deleteAll();

    @Delete
    void deleteArticle(Article entity);

    @Query("SELECT * FROM Article")
    List<Article> findAll();

    @Query("SELECT * FROM Article")
    LiveData<List<Article>> loadSignList();
}

4. 定義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}, // 聲明需要?jiǎng)?chuàng)建表的實(shí)體
        version = 2, // 數(shù)據(jù)庫版本號(hào)
        exportSchema = true  // 表結(jié)構(gòu)是否需要導(dǎo)出
)
@TypeConverters({ConversionFactory.class}) // 屬性類型轉(zhuǎn)換衡查，這里值轉(zhuǎn)換了Date類
public abstract class Database extends RoomDatabase {
    public abstract ArticleDao articleDao(); // 聲明每個(gè)entity的dao類

    private static Database sInstance; // 創(chuàng)建訪問數(shù)據(jù)庫比較耗資源必盖，生成單例方便訪問
    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) // 構(gòu)建版本升級(jí)時(shí)表結(jié)構(gòu)的變化
                .allowMainThreadQueries()
                .build();
    }

    private static Migration MIGRATION_1_2 = new Migration(1,2) {
        @Override
        public 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. 測試

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 {
    @Test
    public 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());
    }
}

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