sqlite 关联表查询

    ContentProvider灵活性并不是很好，这时我们可以直接使用SQLiteOpenHelper来进行数据库操作。个人觉得这才是我知道的数据库，棒棒哒！这里记录一下关联表查询。

1.两个数据结构：BookDao和AuthorDao

/**
 * Created by travis on 2016/3/8.
 */
public class BookDao {
    public static final String TABLE_NAME = "book";
    public static final String ID = "id";
    public static final String BOOK_NAME = "book_name";
    public static final String PRICE = "price";
    public static final String ISBN = "isbn";
    public static final String AUTHOR = "author";

    public static final String CREATE_SQL = "CREATE TABLE " + TABLE_NAME + " ("
            + ID + " INTEGER PRIMARY KEY,"
            + BOOK_NAME + " VARCHAR(32),"
            + PRICE + " VARCHAR(10),"
            + ISBN + " VARCHAR(16),"
            + AUTHOR + " VARCHAR(32)"
            + ");";

    public static final String DROP_SQL = "DROP TABLE IF EXISTS " + TABLE_NAME;
}

/**
 * Created by hsji on 2016/3/8.
 */
public class AuthorDao {
    public static final String TABLE_NAME = "author";
    public static final String ID = "id";
    public static final String AUTHOR_NAME = "author_name";
    public static final String GENDER = "gender";
    public static final String ADDRESS = "address";

    public static final String CREATE_SQL = "CREATE TABLE " + TABLE_NAME + " ("
            + ID + " INTEGER PRIMARY KEY,"
            + AUTHOR_NAME + " VARCHAR(32),"
            + GENDER + " VARCHAR(1),"
            + ADDRESS + " VARCHAR(64)"
            + ");";

    public static final String DROP_SQL = "DROP TABLE IF EXISTS " + TABLE_NAME;
}

2.数据库和java对象的纽带SQLiteOpenHelper

public class DatabaseHelper extends SQLiteOpenHelper {
    public static final String DATABBASE_NAME = "monster.db";
    public static final int DATABASE_VERSION = 3;

    /**
     * 如果如果数据库不存在，创建数据库，如果数据库已经存在，则打开数据库。
     *
     * @param context
     */
    public DatabaseHelper(Context context) {
        super(context, DATABBASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(BookDao.CREATE_SQL);
        db.execSQL(AuthorDao.CREATE_SQL);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL(BookDao.DROP_SQL);
        db.execSQL(AuthorDao.DROP_SQL);
        onCreate(db);
    }
}

3.在程序当中直接使用SQLiteOpenHelper进行数据库操作。

        //获取SQLiteOpenHelper对象，如果数据库已经存在则打开数据库，如果不存在则创建并打开
        DatabaseHelper dBHelper = new DatabaseHelper(TestActivity.this);
        SQLiteDatabase db = dBHelper.getWritableDatabase();
        
        //往book表里添加一本书
        ContentValues cv = new ContentValues();
        cv.put(BookDao.ID, 100);
        cv.put(BookDao.BOOK_NAME, "如何和傻逼相处");
        cv.put(BookDao.AUTHOR, "travis");
        cv.put(BookDao.PRICE, "￥8888");
        cv.put(BookDao.ISBN, "9000123");
        //首先检查数据库中有没有这本书，有的话不再插入，没有的话执行插入操作
        Cursor tem = db.rawQuery("select id from book where id = ?", new String[]{"100"});
        if (tem.getCount() != 0) {
            Log.d(TAG, "Book 已经存在该键值");
        } else {
            db.insert(BookDao.TABLE_NAME, null, cv);
        }
        //往author表里添加一个作者
        ContentValues cv1 = new ContentValues();
        cv1.put(AuthorDao.ID, 100);
        cv1.put(AuthorDao.AUTHOR_NAME, "travis");
        cv1.put(AuthorDao.GENDER, "M");
        cv1.put(AuthorDao.ADDRESS, "上海");
        Cursor tem1 = db.rawQuery("select id from author where id = ?", new String[]{"100"});
        if (tem1.getCount() != 0) {
            Log.d(TAG, "Author 已经存在该键值");
        } else {
            db.insert(AuthorDao.TABLE_NAME, null, cv1);
        }
        //通过rawQuery()方法实现关联表查询
        Cursor cursor = db.rawQuery("select book.id as id,book_name,author_name from " + BookDao.TABLE_NAME + "," + AuthorDao.TABLE_NAME + " where book.author = author.author_name", new String[]{});
        //输出查询到的数据
        cursor.moveToNext();
        while (!cursor.isAfterLast()) {
            Log.d(TAG, "book_name=" + cursor.getString(cursor.getColumnIndex(BookDao.BOOK_NAME)));
            Log.d(TAG, "author_name=" + cursor.getString(cursor.getColumnIndex(AuthorDao.AUTHOR_NAME)));
            cursor.moveToNext();
        }