安卓Sqlite數據庫

參考視頻學習:https://www.bilibili.com/video/BV1wt411n7pz
查看數據庫的軟件 SQLite Expert
從編譯器右下角打開的模擬器中找到對應項目的數據庫文件,然後添加到軟件中去查看

• 創建數據庫
• Dao層去增刪改查
• 一個常量類去管理

public class Constants {

    public static final String DATABASE_NAME = "test.db";

    public static final int DATABASE_VERSION = 3;

    public static final String TABLE_NAME = "employee";
    
}

Sql語言版

public class Dao {

   private DatabaseHelper mHelper;
   private static final String TAG = "Dao";

   public Dao(Context context) {
       //創建數據庫
       mHelper = new DatabaseHelper(context);
   }

   public void insert() {
       SQLiteDatabase db = mHelper.getWritableDatabase();
       String sql = "insert into "+Constants.TABLE_NAME+"(_id,name,age,salary,phone,average,address) " +
               "values(?,?,?,?,?,?,?)";
       db.execSQL(sql,new Object[]{1,"Mike",60,111,110,55,"USA"});
       db.close();
   }

   public void delete() {
       SQLiteDatabase db = mHelper.getWritableDatabase();
       String sql = "delete from "+Constants.TABLE_NAME+" where age = 60";
       db.execSQL(sql);
       db.close();
   }

   public void update() {
       SQLiteDatabase db = mHelper.getWritableDatabase();
       String sql = "update "+Constants.TABLE_NAME+" set salary = 2 where age = 60";
       db.execSQL(sql);
       db.close();
   }

   public void query() {
       SQLiteDatabase db = mHelper.getWritableDatabase();
       String sql = "select * from "+Constants.TABLE_NAME;
       Cursor cursor = db.rawQuery(sql, null);
       while (cursor.moveToNext()) {
           //返回name是第幾列
           int index = cursor.getColumnIndex("name");
           //返回name那一列的並轉成字符串
           String name = cursor.getString(index);
           Log.e(TAG, "query: "+name );
       }
       cursor.close();
       db.close();
   }
}

使用API版本的

public class Dao {

    private DatabaseHelper mHelper;
    private static final String TAG = "Dao";

    public Dao(Context context) {
        //創建數據庫
        mHelper = new DatabaseHelper(context);
    }

    public void insert() {
        SQLiteDatabase db = mHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("_id",2);
        values.put("name","Tom");
        values.put("age",20);
        values.put("salary",100);
        values.put("phone",120);
        values.put("average",123);
        values.put("address","China");
        db.insert(Constants.TABLE_NAME,null,values);

        db.close();
    }

    public void delete() {
        SQLiteDatabase db = mHelper.getWritableDatabase();
        db.delete(Constants.TABLE_NAME,"age=?",new String[]{"20"});
        db.close();
    }

    public void update() {
        SQLiteDatabase db = mHelper.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put("age",50);
        db.update(Constants.TABLE_NAME,values,"name = ?",new String[]{"Tom"});
        db.close();
    }

    public void query() {
        SQLiteDatabase db = mHelper.getWritableDatabase();
        Cursor cursor = db.query(Constants.TABLE_NAME, null, "age = 50", null, null, null, null);
        while (cursor.moveToNext()){
            Log.e(TAG, "name->"+cursor.getString(cursor.getColumnIndex("name")));
        }
        cursor.close();
        db.close();
    }
}

• 測試類測試

@RunWith(AndroidJUnit4.class)
public class TestDatabase {
    Context context = InstrumentationRegistry.getInstrumentation().getTargetContext();

    @Test
    public void testCreate() {

    }
    @Test
    public void testInsert() {
        Dao dao = new Dao(context);
        dao.insert();
    }
    @Test
    public void testDelete() {
        Dao dao = new Dao(context);
        dao.delete();
    }
    @Test
    public void testUpdate() {
        Dao dao = new Dao(context);
        dao.update();
    }
    @Test
    public void testQuery() {
        Dao dao = new Dao(context);
        dao.query();
    }
}

• 數據庫事務
  兩個特點
  • 安全性
    比如公司有一百萬,你的工資是一萬,當工資給你發工資時,這時突然停電,公司賬戶少了一萬,但你的賬戶沒有增加錢,這就是安全性不夠.
    安全性:當有異常時就會兩個都不變,不發生異常時會正常變化

public class DataBaseHelper extends SQLiteOpenHelper {
    private static final String TABLE_NAME = "account";
    public DataBaseHelper(@Nullable Context context) {
        super(context, "test.db", null, 1);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String sql = "create table "+TABLE_NAME+"(_id integer,name varchar,money integer)";
        db.execSQL(sql);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }
}

@RunWith(AndroidJUnit4.class)
public class TestDataBase {

    Context context = InstrumentationRegistry.getInstrumentation().getTargetContext();
    private DataBaseHelper mHelper = new DataBaseHelper(context);

    @Test
    public void testDataBase() {
        mHelper.getWritableDatabase();
    }

    @Test
    public void testInsert() {
        SQLiteDatabase db = mHelper.getWritableDatabase();
        String sql = "insert into account values (1,'company',1000000)";
        String sql1 = "insert into account values (2,'my_count',0)";
        db.execSQL(sql);
        db.execSQL(sql1);
    }

	//當有異常時就會兩個都不變,不發生異常時會正常變化
    @Test
    public void testUpdate() {
        SQLiteDatabase db = mHelper.getWritableDatabase();
        db.beginTransaction();
        try {
            String sql = "update account set money = 1000000 - 10000 where name = 'company'";
            //int i = 10 / 0;
            String sql1 = "update account set money = 10000 where name = 'my_count'";
            db.execSQL(sql);
            db.execSQL(sql1);
            db.setTransactionSuccessful();
        }catch (Exception e){
            throw new RuntimeException("發生異常!");
        }finally {
            db.endTransaction();
            db.close();
        }
    }

}

• 高效性
  添加大量數據時,使用的時間長短
  加上這兩句,效率會提升幾十倍,因爲添加後數據一次性添加進去,而不是一條一條地添加
  db.beginTransaction();
  db.endTransaction();

@Test
    public void testInsert() {
        SQLiteDatabase db = mHelper.getWritableDatabase();
        Long start = System.currentTimeMillis();
        db.beginTransaction();
        for(int i=0;i<3000;i++) {
            String sql = "insert into account values (1,'company',1000000)";
            db.execSQL(sql);
        }
        db.endTransaction();
        Log.e(TAG, "time -> " + (System.currentTimeMillis() - start) );
    }