android - android studio中的数据库

Question

<分区>

Answer 1

要创建数据库，您需要扩展 SQLiteOpenHelper 并需要一个采用 Context 的构造函数。 假设您将此类命名为 DBOperator。表创建过程看起来像这样，

public class DbOperator extends SQLiteOpenHelper {

    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "DB_NAME";
    protected static final String FIRST_TABLE_NAME = "FIRST_TABLE";
    protected static final String SECOND_TABLE_NAME = "SECOND_TABLE";

    public static final String CREATE_FIRST_TABLE = "create table if not exists "
            + FIRST_TABLE_NAME
            + " ( _id integer primary key autoincrement, COL1  TEXT NOT NULL, COL2 TEXT NOT NULL,COL3 TEXT, COL4 int, COL5 TEXT,"
            + "COL6 TEXT,COL7 REAL, COL8 INTEGER,COL9 TEXT not null);";

    public static final String CREATE_SECOND_TABLE = "create table if not exists "
            + SECOND_TABLE_NAME+.........

    public DbOperator(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(CREATE_SFIRST_TABLE);
        db.execSQL(CREATE_SECOND_TABLE);
        //db.close();
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        //THIS WILL BE EXECUTED WHEN YOU UPDATED VERSION OF DATABASE_VERSION
        //YOUR DROP AND CREATE QUERIES
    }
}

---

现在您的数据操作类(添加、删除、更新)看起来像这样，

public class FirstTableDML extends DbOperator {

    public FirstTableDML(Context context) {
        super(context);
    }

    private static final String COL_ID = "_id";
    private static final String COL1 = "COL1";
    private static final String COL2 = "COL2";
    ........
    .......

    public void deleteFirstTableDataList(List<FirstTableData> firstTableDataList) {
        for (FirstTableData data : firstTableDataList)
            deleteFirstTableDetailData(data);
    }
    public void deleteFirstTableDetailData(FirstTableData item) {
        SQLiteDatabase db = this.getWritableDatabase();
        db.delete(FIRST_TABLE_NAME, item.getId() + "=" + COL_ID, null);
        db.close();
    }
    /**this method retrieves all the records from table and returns them as list of  
     FirstTableData types. Now you use this list to display detail on your screen as per your 
    requirements.
    */
    public List< FirstTableData > getFirstTableDataList() {
        List< FirstTableData > firstTableDataList = new ArrayList< FirstTableData >();
        String refQuery = "Select * From " + FIRST_TABLE_NAME;
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(refQuery, null);
        try {
            if (cursor.moveToFirst()) {
                do {
                    FirstTableData itemData = new FirstTableData();

                    itemData.setId(cursor.getInt(0));

                    itemData.setCol1(cursor.getString(1));
                    itemData.setCol2(cursor.getInt(2));
                    .....
                    .....

                    firstTableDataList.add(itemData);
                } while (cursor.moveToNext());
            }
        } finally {

            db.close();
        }

        Collections.sort(itemDataList);
        return itemDataList;
    }

    public int  addFirstTableData(FirstTableData data) {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues values = new ContentValues();

        values.put(COL1, data.getCol1());
        values.put(COL2, data.getCol2());
        .....
        .....
        long x=db.insert(FIRST_TABLE_NAME, null, values);
        db.close();
        return (int)x;
    }

    public void updateItemDetailData(FirstTableData data) {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues values = new ContentValues();

        values.put(COL1, data.getCol1());
        values.put(COL2, data.getCol2());
        values.put(COL3, data.getCol3());
        .....
        .....


        db.update(FIRST_TABLE_NAME, values, COL_ID + "=" + data.getId(),    null);
        db.close();
    }

}

P.S : *数据类是代表对应表的POJO数据类。 既然你说你对这些并不陌生，我没有提供任何帮助评论，因为大多数方法名称都是不言自明的。 希望它能帮助您入门。