sqlite 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();
}