Android项目中，在一个数据库里建立多张表
一，创建一个公共的DBAdapter;
为了在整个程序运行期间调用该公共的数据库，我们定义了一个扩展自Application的CommDB类：
1，创建唯一的数据库：
1 public class CommDB { 2 3 public static final String DATABASE_NAME = "myDatabase"; //数据库名称 4 5 public static final int DATABASE_VERSION = 1; 6 //创建该数据库下学生表的语句 7 private static final String CREATE_TABLE_Students = 8 "CREATE TABLE if not exists " + StudentDB.SQLITE_TABLE + " (" + 9 StudentDB.KEY_ROWID + " integer PRIMARY KEY autoincrement," + 10 StudentDB.KEY_AGE + "," + 11 StudentDB.KEY_GENDER + "," + 12 StudentDB.KEY_NAME + "," + 13 " UNIQUE (" + StudentDB.KEY_NAME +"));";//暂时规定不能重名 14 //创建该数据库下教师表的语句 15 private static final String CREATE_TABLE_Teachers = 16 "CREATE TABLE if not exists " + TeacherDB.SQLITE_TABLE + " (" + 17 TeacherDB.KEY_ROWID + " integer PRIMARY KEY autoincrement," + 18 TeacherDB.KEY_AGE + "," + 19 TeacherDB.KEY_GENDER + "," + 20 TeacherDB.KEY_NAME + "," + 21 " UNIQUE (" + TeacherDB.KEY_AGE +"));"; 22 private final Context context; 23 private DatabaseHelper DBHelper; 24 private SQLiteDatabase db; 25 /** 26 * Constructor 27 * @param ctx 28 */ 29 public CommDB(Context ctx) 30 { 31 this.context = ctx; 32 this.DBHelper = new DatabaseHelper(this.context); 33 } 34 35 private static class DatabaseHelper extends SQLiteOpenHelper 36 { 37 DatabaseHelper(Context context) 38 { 39 super(context, DATABASE_NAME, null, DATABASE_VERSION); 40 } 41 42 @Override 43 public void onCreate(SQLiteDatabase db) 44 { 45 db.execSQL(CREATE_TABLE_Students);//创建学生表 46 db.execSQL(CREATE_TABLE_Teachers);//创建教师表 47 } 48 49 @Override 50 public void onUpgrade(SQLiteDatabase db, int oldVersion, 51 int newVersion) 52 { 53 // Adding any table mods to this guy here 54 } 55 } 56 57 /** 58 * open the db 59 * @return this 60 * @throws SQLException 61 * return type: DBAdapter 62 */ 63 public CommDB open() throws SQLException 64 { 65 this.db = this.DBHelper.getWritableDatabase(); 66 return this; 67 } 68 69 /** 70 * close the db 71 * return type: void 72 */ 73 public void close() 74 { 75 this.DBHelper.close(); 76 } 77 }
2，在app开始运行时，创建上述的数据库，并创建对应的数据表：
1 public class GApplication extends Application { 2 private CommDB comDBHelper; 3 4 @Override 5 public void onCreate() { 6 // TODO Auto-generated method stub 7 super.onCreate(); 8 comDBHelper = new CommDB(this); 9 comDBHelper.open(); 10 } 11 12 }
二，分别创建对应的数据表；
1，建立学生数据表类：
public class StudentDB { public static final String KEY_ROWID = "_id"; public static final String KEY_AGE = "age"; public static final String KEY_GENDER = "gender"; public static final String KEY_NAME = "name"; private static final String TAG = "StudentDbAdapter"; private DatabaseHelper mDbHelper; private SQLiteDatabase mDb; // private static final String DATABASE_NAME = "Fortrun_Ticket11"; static final String SQLITE_TABLE = "StudentTable"; private final Context mCtx; private static class DatabaseHelper extends SQLiteOpenHelper { DatabaseHelper(Context context) { super(context, CommDB.DATABASE_NAME, null, CommDB.DATABASE_VERSION); } @Override public void onCreate(SQLiteDatabase db) { } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { Log.w(TAG, "Upgrading database from version " + oldVersion + " to " + newVersion + ", which will destroy all old data"); db.execSQL("DROP TABLE IF EXISTS " + SQLITE_TABLE); onCreate(db); } } public StudentDB(Context ctx) { this.mCtx = ctx; } public StudentDB open() throws SQLException { mDbHelper = new DatabaseHelper(mCtx); mDb = mDbHelper.getWritableDatabase(); return this; } public void close() { if (mDbHelper != null) { mDbHelper.close(); } } /** * 创建学生表的字段 * @param age * @param gender * @param name * @return */ public long createStudent(String age, String gender, String name) { long createResult = 0; ContentValues initialValues = new ContentValues(); initialValues.put(KEY_AGE, age); initialValues.put(KEY_GENDER, gender); initialValues.put(KEY_NAME, name); try { createResult = mDb.insert(SQLITE_TABLE, null, initialValues); } catch (Exception e) { // TODO: handle exception } return createResult; } /** * 删除表的全部字段数据 * @return */ public boolean deleteAllStudents() { int doneDelete = 0; try { doneDelete = mDb.delete(SQLITE_TABLE, null, null); Log.w(TAG, Integer.toString(doneDelete)); Log.e("doneDelete", doneDelete + ""); } catch (Exception e) { // TODO: handle exception e.printStackTrace(); } return doneDelete > 0; } /** * 根据名称删除表中的数据 * @param name * @return */ public boolean deleteTicketByName(String name) { int isDelete; String[] tName; tName = new String[] { name }; isDelete = mDb.delete(SQLITE_TABLE, KEY_AGE + "=?", tName); Log.e("deleteTicket", "isDelete:" + isDelete + "||" + "ticketID=" + name); return isDelete > 0; } public void insertSomeTickets() { } /** * 获取表中的所有字段 * @return */ public ArrayList<Student> fetchAll() { ArrayList<Student> allTicketsList = new ArrayList<Student>(); Cursor mCursor = null; mCursor = mDb.query(SQLITE_TABLE, new String[] { KEY_ROWID, KEY_AGE, KEY_GENDER, KEY_NAME }, null, null, null, null, null); if (mCursor.moveToFirst()) { do { Student st = new Student(); st.setAge(mCursor.getString(mCursor .getColumnIndexOrThrow(KEY_AGE))); st.setGender(mCursor.getString(mCursor .getColumnIndexOrThrow(KEY_GENDER))); st.setName(mCursor.getString(mCursor .getColumnIndexOrThrow(KEY_NAME))); allTicketsList.add(st); } while (mCursor.moveToNext()); } if (mCursor != null && !mCursor.isClosed()) { mCursor.close(); } return allTicketsList; } }
2，创建教师数据表类：
public class TeacherDB { public static final String KEY_ROWID = "_id"; public static final String KEY_AGE = "age"; public static final String KEY_GENDER = "gender";// 还要保留 public static final String KEY_NAME = "name"; private static final String TAG = "TeacherDbAdapter"; private DatabaseHelper mDbHelper; private SQLiteDatabase mDb; // private static final String DATABASE_NAME = "Fortrun_Ticket11"; static final String SQLITE_TABLE = "TeacherTable"; private static final int DATABASE_VERSION = 1; private final Context mCtx; private static class DatabaseHelper extends SQLiteOpenHelper { DatabaseHelper(Context context) { super(context, CommDB.DATABASE_NAME, null, CommDB.DATABASE_VERSION); } @Override public void onCreate(SQLiteDatabase db) { // Log.w(TAG, DATABASE_CREATE); // db.execSQL(DATABASE_CREATE); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { Log.w(TAG, "Upgrading database from version " + oldVersion + " to " + newVersion + ", which will destroy all old data"); db.execSQL("DROP TABLE IF EXISTS " + SQLITE_TABLE); onCreate(db); } } public TeacherDB(Context ctx) { this.mCtx = ctx; } public TeacherDB open() throws SQLException { mDbHelper = new DatabaseHelper(mCtx); mDb = mDbHelper.getWritableDatabase(); return this; } public void close() { if (mDbHelper != null) { mDbHelper.close(); } } public long createTeacher(String age, String gender, String name) { long createResult = 0; ContentValues initialValues = new ContentValues(); initialValues.put(KEY_AGE, age); initialValues.put(KEY_GENDER, gender); initialValues.put(KEY_NAME, name); try { createResult = mDb.insert(SQLITE_TABLE, null, initialValues); } catch (Exception e) { // TODO: handle exception } return createResult; } public boolean deleteAllTeachers() { int doneDelete = 0; try { doneDelete = mDb.delete(SQLITE_TABLE, null, null); Log.w(TAG, Integer.toString(doneDelete)); Log.e("doneDelete", doneDelete + ""); } catch (Exception e) { // TODO: handle exception e.printStackTrace(); } return doneDelete > 0; } public boolean deleteTeacherByName(String name) { int isDelete; String[] tName; tName = new String[] { name }; isDelete = mDb.delete(SQLITE_TABLE, KEY_AGE + "=?", tName); Log.e("deleteTicket", "isDelete:" + isDelete + "||" + "ticketID=" + name); return isDelete > 0; } public void insertSomeTickets() { } // 扫描时进行判断本地数据库是否有此ticketID public ArrayList<Teacher> fetchAll() { ArrayList<Teacher> allTeacherList = new ArrayList<Teacher>(); Cursor mCursor = null; mCursor = mDb.query(SQLITE_TABLE, new String[] { KEY_ROWID, KEY_AGE, KEY_GENDER, KEY_NAME }, null, null, null, null, null); if (mCursor.moveToFirst()) { do { Teacher st = new Teacher(); st.setAge(mCursor.getString(mCursor .getColumnIndexOrThrow(KEY_AGE))); st.setGender(mCursor.getString(mCursor .getColumnIndexOrThrow(KEY_GENDER))); st.setName(mCursor.getString(mCursor .getColumnIndexOrThrow(KEY_NAME))); allTeacherList.add(st); } while (mCursor.moveToNext()); } if (mCursor != null && !mCursor.isClosed()) { mCursor.close(); } return allTeacherList; } }
三，调用public class ShowActivity extends Activity {
private StudentDB studentDB; private TeacherDB teacherDB; private List<Student> stList = new ArrayList<Student>(); private List<Teacher> trList = new ArrayList<Teacher>(); @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_show); studentDB = new StudentDB(this); studentDB.open(); teacherDB = new TeacherDB(this); teacherDB.open(); studentDB.createStudent("28", "男", "阿武"); studentDB.createStudent("24", "女", "小铃"); teacherDB.createTeacher("40", "男", "何SIR"); teacherDB.createTeacher("45", "女", "MRS谢"); stList = studentDB.fetchAll(); trList = teacherDB.fetchAll(); for (int i = 0; i < stList.size(); i++) { Log.e("stList value", stList.get(i).getName()); } for (int i = 0; i < trList.size(); i++) { Log.e("trList value", trList.get(i).getName()); } }
@Override protected void onDestroy() { // TODO Auto-generated method stub super.onDestroy(); if (studentDB != null) { studentDB.close(); } if (teacherDB != null) { teacherDB.close(); } } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.show, menu); return true; } }
四，结果验证；
10-25 16:50:10.321: E/stList value(3953): 阿武
10-25 16:50:10.321: E/stList value(3953): 小铃
10-25 16:50:10.321: E/trList value(3953): 何SIR
10-25 16:50:10.321: E/trList value(3953): MRS谢
五，注意事项：
此例子中插入数据库的数据是以年龄作为唯一字段，当插入的数据中，年龄字段有重复时，数据库会报错，此例子只为说明如何在一个数据库中建立多张表，因此，在实际项目中，一般以某个实体的ID作为唯一字段，且插入前必须经过判断；
另外，数据库的关闭，我们选择在onDestroy()方法中调用。
