數據庫框架Room1 初體驗

使用Room來操作sqlite數據庫十分方便

1. 創建依賴，下方代碼來自官方

    def room_version = "2.2.3"

    implementation "androidx.room:room-runtime:$room_version"
    annotationProcessor "androidx.room:room-compiler:$room_version" // For Kotlin use kapt instead of annotationProcessor

    // optional - Kotlin Extensions and Coroutines support for Room
    implementation "androidx.room:room-ktx:$room_version"

    // optional - RxJava support for Room
    implementation "androidx.room:room-rxjava2:$room_version"

    // optional - Guava support for Room, including Optional and ListenableFuture
    implementation "androidx.room:room-guava:$room_version"

    // Test helpers
    testImplementation "androidx.room:room-testing:$room_version"

可能需要在修改項目的gradle而非模塊的gradle文件如下，否則可能會導致編譯的時候失敗

buildscript {
    repositories {
        google()
        maven { url 'http://maven.aliyun.com/nexus/content/groups/public/'}
        maven { url'https://maven.aliyun.com/repository/public/' }
        maven { url'https://maven.aliyun.com/repository/google/' }
        maven { url'https://maven.aliyun.com/repository/jcenter/' }
        maven { url'https://maven.aliyun.com/repository/central/' }
        jcenter()
        
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:3.5.1'
        
        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
}

allprojects {
    repositories {
        google()
        maven { url 'http://maven.aliyun.com/nexus/content/groups/public/'}
        maven { url'https://maven.aliyun.com/repository/public/' }
        maven { url'https://maven.aliyun.com/repository/google/' }
        maven { url'https://maven.aliyun.com/repository/jcenter/' }
        maven { url'https://maven.aliyun.com/repository/central/' }
        jcenter()
    }
}

2. 創建一個實體類(entity)

注意代碼中的註釋，通過字面意思應該能判斷註釋的作用

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

@Entity
public class Word {

    @PrimaryKey(autoGenerate = true)
    private int id;

    @ColumnInfo(name = "word")
    private String word;
    @ColumnInfo(name = "chinese_meaning")
    private String chineseMeaning;

    public Word(){

    };

    public Word(String word, String chineseMeaning) {
        this.word = word;
        this.chineseMeaning = chineseMeaning;
    }

    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 getChineseMeaning() {
        return chineseMeaning;
    }

    public void setChineseMeaning(String chineseMeaning) {
        this.chineseMeaning = chineseMeaning;
    }
}

3. 創建dao層接口

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
public interface WordDao {

    @Insert
    void insertWords(Word... words);

    @Update
    void updateWords(Word... words);

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

    @Query("delete from word")
    void deleteAllWords();

    @Query("select * from word order by id desc")
    List<Word> getAllWords();

}

4. 創建database抽象類

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

@Database(entities = {Word.class}, version = 1,exportSchema = false)
public abstract class WordDatabase extends RoomDatabase {

    public abstract WordDao getWordDao();
}

5. 在Activity中使用

import android.os.Bundle;
import android.widget.Button;
import android.widget.TextView;

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

import java.util.List;

public class MainActivity extends AppCompatActivity {

    WordDatabase wordDatabase;
    WordDao wordDao;
    TextView textView;
    Button btnInsert, btnUpdate, btnClear, btnDelete;

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

        wordDatabase = Room.databaseBuilder(this, WordDatabase.class, "word_database")
                .allowMainThreadQueries()
                .build();
        wordDao = wordDatabase.getWordDao();

        textView = findViewById(R.id.textView);

        updateView();

        btnInsert = findViewById(R.id.btnInsert);
        btnUpdate = findViewById(R.id.btnUpdate);
        btnClear = findViewById(R.id.btnClear);
        btnDelete = findViewById(R.id.btnDelete);

        btnInsert.setOnClickListener(v -> {
            Word word1 = new Word("Hello", "你好");
            Word word2 = new Word("World", "世界");
            wordDao.insertWords(word1, word2);
            updateView();
        });

        btnUpdate.setOnClickListener(v -> {
            Word word = new Word("Hi", "你好啊");
            word.setId(1);
            wordDao.updateWords(word);
            updateView();
        });

        btnClear.setOnClickListener(v -> {
            wordDao.deleteAllWords();
            updateView();
        });

        btnDelete.setOnClickListener(v -> {
            Word word = new Word();
            word.setId(10);
            wordDao.deleteWords(word);
            updateView();
        });

    }

    void updateView(){
        List<Word> words = wordDao.getAllWords();
        String text = "";
        for (Word word : words) {
            text += word.getId() + ": " + word.getWord() + " = " + word.getChineseMeaning() + "\n";
        }
        textView.setText(text);
    }

}