数据库room简单使用_dataroom 使用教程

数据库room简单使用（参考官网）

三步走

1、建立实体类

2、建立Dao

3、继承虚基类RoomDatabase

引入数据库：

 defaultConfig {
        javaCompileOptions {
            annotationProcessorOptions {
                arguments += [
                        "room.schemaLocation":"$projectDir/schemas".toString(),
                        "room.incremental":"true",
                        "room.expandProjection":"true"]
            }
        }
    }    
dependencies {
    def room_version = "2.4.2"
    implementation "androidx.room:room-runtime:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version"
}
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---

1、建立实体类

@Entity 注解必须加

这个注释将类标记为数据库行。对于每个实体，将创建一个数据库表来保存项目。Entity类必须在database# entities数组中被引用。实体(及其超类)的每个字段都持久化在数据库中，除非另有说明(详见实体文档)。

@PrimaryKey 主键，autoGenerate 指明是否自增长；@ColumnInfo 列的信息，有名称 、数据类型等等

import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;

@Entity
public class Song {

    @PrimaryKey(autoGenerate = true)
    private int id;
    private String name;
    @ColumnInfo(name = "release_year")
    private int releaseYear;

    public Song(String name, int releaseYear) {
        this.name = name;
        this.releaseYear = releaseYear;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getReleaseYear() {
        return releaseYear;
    }

    public void setReleaseYear(int releaseYear) {
        this.releaseYear = releaseYear;
    }
}
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2、建立Dao

增删改查语句，也是采用注解方式，同样@Dao一定不可少

import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.Query;

import java.util.List;

@Dao
public interface SongDao {

    @Query("SELECT * FROM song")
    List<Song> loadAll();

    @Query("SELECT * FROM song WHERE id IN (:songIds)")
    List<Song> loadAllBySongId(int... songIds);

    @Query("SELECT * FROM song WHERE name LIKE :name AND release_year = :year LIMIT 1")
    Song loadOneByNameAndReleaseYear(String name, int year);

    @Insert
    void insertAll(Song... songs);

    @Insert
    void insert(Song song);

    @Delete
    void delete(Song song);
}
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3、继承虚基类RoomDatabase

@Database(entities = {Song.class}, version = 1) ，指明注解entitie和版本

import androidx.room.Database;
import androidx.room.RoomDatabase;

@Database(entities = {Song.class}, version = 1)
public abstract class MusicDatabase extends RoomDatabase {
    public abstract SongDao songDao();
}
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最后使用：

需要注意的是数据库操作要在子线程中进行，可以使用线程池或者别的调用子线程方式。

import android.os.Bundle;
import android.util.Log;

import androidx.appcompat.app.AppCompatActivity;
import androidx.room.Room;

import com.deviser.room.db.MusicDatabase;
import com.deviser.room.db.Song;

import java.util.List;

public class MainActivity extends AppCompatActivity {

    MusicDatabase mDB;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mDB = Room.databaseBuilder(getApplicationContext(), MusicDatabase.class, "xx-db").build();

        findViewById(R.id.insert).setOnClickListener(v -> {
            new Thread(() -> {
                Song s1 = new Song("潇洒走一回", 1991);
                mDB.songDao().insert(s1);
            }).start();
        });
        findViewById(R.id.search).setOnClickListener(v -> {
            new Thread(() -> {
                List<Song> list = mDB.songDao().loadAll();
                for (Song s : list) {
                    Log.i("TAG", "当前项在库中的id:" + s.getId() + ",歌曲名：" + s.getName() + ",发行年代：" + s.getReleaseYear());
                }
            }).start();
        });
    }

}

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