AndroidX Room管理数据库 App50

简易实现Room管理Sqlite数据库

数据库要放那种数据 实体行Entity 和列

import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;
@Entity
public class Word {
    @PrimaryKey (autoGenerate = true)//行主键 由系统自动生成
    private int id ;
    @ColumnInfo(name = "English_name")//列的名称，不写也可以会默认为变量名word
    private String word;
    @ColumnInfo(name = "Chinese_name")
    private String meaning;
    public Word(){
    }
    //设置构造方法
    public Word(String word, String meaning) {
        this.word = word;
        this.meaning = meaning;
    }
    //设置变量的getter和setter ID的setter可以不用写因为系统会自动生成
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getWord() {
        return word;
    }
    public void setWord(String word) {
        this.word = word;
    }
    public String getMeaning() {
        return meaning;
    }
    public void setMeaning(String meaning) {
        this.meaning = meaning;
    }
}

Dao层

import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.Query;
import androidx.room.Update;
import java.util.List;

@Dao //Database access object 也可以声明为抽象类或者接口
   //最关键的类，数据库操作的接口 控制操作数据库的各种方法
public interface WordDao {

   @Insert //修饰词的作用在于让系统编译的时候自动生成相关的代码
   // Word...表示可以传递一个或者多个参数，返回值可以是void或者是long 返回一个插入后的id
   void insertWord(Word... words);

   @Update
   //返回值可以是void 或者是int 返回修改了多少条数据,这条代码修改了多少条记录
   void  updateWord(Word... words);

   @Delete
   void deleteWord(Word... words);

   //习惯性SQL语句都用大写
   @Query("DELETE FROM WORD")
   void deleteAllword();

   @Query("SELECT * FROM WORD ORDER BY ID DESC")
   List<Word> getAllWord();

}

Database抽象类继承RoomDatabase的抽象类

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

//实现的代码都不需要自己写 所以声明为抽象类
@Database(entities = {Word.class},version = 1,exportSchema = false)
public abstract class WordDatabase extends RoomDatabase {

    //若有多个Entities实体应该写多个Dao
    public abstract WordDao getWordDao();

}

在MainAtivity中的操作

import androidx.appcompat.app.AppCompatActivity;
import androidx.room.Room;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    WordDao wordDao;
    WordDatabase wordDatabase;
    Button update,delete,deleteAll,add;
    TextView textView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView=findViewById(R.id.textView);
        update=findViewById(R.id.update);
        delete=findViewById(R.id.delete);
        deleteAll=findViewById(R.id.deleteAll);
        add=findViewById(R.id.add);
        wordDatabase= Room.databaseBuilder(this,WordDatabase.class,"word_database")
                .allowMainThreadQueries()//数据库中的操作一般不在主线程 这里强行在主线层中进行操作
                .build();
        wordDao=wordDatabase.getWordDao();
        updateView();

        add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Word word=new Word("OJBK","很欧尅");
                Word word1=new Word("Total","完全");
                wordDao.insertWord(word,word1);
                updateView();
            }
        });

        update.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Word word=new Word("kkkk","看看看看");
                word.setId(53);
                wordDao.updateWord(word);
                updateView();
            }
        });

        deleteAll.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                wordDao.deleteAllword();
                updateView();
            }
        });
        delete.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Word word=new Word();
                word.setId(52);
                wordDao.deleteWord(word);
                updateView();
            }
        });
    }
    public void updateView(){
        List<Word> words=wordDao.getAllWord();
        String s="";
        for (int i=0;i<words.size();i++){
            Word word=words.get(i);
            s+=word.getId()+": "+word.getWord()+": "+word.getMeaning()+"\n";
        }
        textView.setText(s);
    }
}