Jak usunąć tabele i bazy danych za pomocą Sqiltehelper w Androidzie

Question

Utworzono wywołanie klasy DatabaseHandler rozszerzające SQLiteOpenHelper. Chcę wykreślić usuniętą bazę danych lub tabelę po kliknięciu przycisku. Jakie są parametry, które muszę przekazać do metody połączenia? Oto kod dla odniesienia:

public class DatabaseHandler extends SQLiteOpenHelper 
{ 

// All Static variables 
// Database Version 
public static final int DATABASE_VERSION =1; 

// Database Name 
public static final String DATABASE_NAME = "EmployeeDB"; 

// Contacts table name 
public static final String TABLE_CONTACTS = "contacts"; 

// Contacts Table Columns names 
private static final String KEY_ID = "id"; 
private static final String KEY_NAME = "name"; 
private static final String KEY_PH_NO = "phone_number"; 
public DatabaseHandler(Context context) 
{ 
    super(context, DATABASE_NAME, null, DATABASE_VERSION); 
} 


@Override 
public void onCreate(SQLiteDatabase db) 
{ 
    // TODO Auto-generated method stub 

    String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_CONTACTS + "(" 
    + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT," 
    + KEY_PH_NO + " TEXT" + ")"; 
    db.execSQL(CREATE_CONTACTS_TABLE); 

} 

@Override 
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) 
{ 
    // TODO Auto-generated method stub 
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS); 

     // Create tables again 
     onCreate(db); 

} 

/** 
* All CRUD(Create, Read, Update, Delete) Operations 
*/ 

// Adding new contact 
void addContact(Contact contact) { 
    SQLiteDatabase db = this.getWritableDatabase(); 

    ContentValues values = new ContentValues(); 
    values.put(KEY_NAME, contact.getName()); // Contact Name 
    values.put(KEY_PH_NO, contact.getPhoneNumber()); // Contact Phone 

    // Inserting Row 
    db.insert(TABLE_CONTACTS, null, values); 
    db.close(); // Closing database connection 
} 

// Getting single contact 
Contact getContact(int id) { 
    SQLiteDatabase db = this.getReadableDatabase(); 

    Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID, 
      KEY_NAME, KEY_PH_NO }, KEY_ID + "=?", 
      new String[] { String.valueOf(id) }, null, null, null, null); 
    if (cursor != null) 
     cursor.moveToFirst(); 

    Contact contact = new Contact(id, cursor.getString(1), cursor.getString(2)); 
    // return contact 
    return contact; 
} 

// Getting All Contacts 
public List<Contact> getAllContacts() { 
    List<Contact> contactList = new ArrayList<Contact>(); 
    // Select All Query 
    String selectQuery = "SELECT * FROM " + TABLE_CONTACTS; 

    SQLiteDatabase db = this.getWritableDatabase(); 
    Cursor cursor = db.rawQuery(selectQuery, null); 

    // looping through all rows and adding to list 
    if (cursor.moveToFirst()) { 
     do { 
      Contact contact = new Contact(); 
      contact.setID(Integer.parseInt(cursor.getString(0))); 
      contact.setName(cursor.getString(1)); 
      contact.setPhoneNumber(cursor.getString(2)); 
      // Adding contact to list 
      contactList.add(contact); 
     } while (cursor.moveToNext()); 
    } 

    // return contact list 
    return contactList; 
} 

// Updating single contact 
public int updateContact(Contact contact) { 
    SQLiteDatabase db = this.getWritableDatabase(); 

    ContentValues values = new ContentValues(); 
    values.put(KEY_NAME, contact.getName()); 
    values.put(KEY_PH_NO, contact.getPhoneNumber()); 

    // updating row 
    return db.update(TABLE_CONTACTS, values, KEY_ID + " = ?", 
      new String[] { String.valueOf(contact.getID()) }); 
} 

// Deleting single contact 
public void deleteContact(Contact contact) { 
    SQLiteDatabase db = this.getWritableDatabase(); 
    db.delete(TABLE_CONTACTS, KEY_ID + " = ?", 
      new String[] { String.valueOf(contact.getID()) }); 
    db.close(); 
} 

// Getting contacts Count 
public int getContactsCount() { 
    String countQuery = "SELECT * FROM " + TABLE_CONTACTS; 
    SQLiteDatabase db = this.getReadableDatabase(); 
    Cursor cursor = db.rawQuery(countQuery, null); 
    cursor.close(); 

    // return count 
    return cursor.getCount(); 
} 
public void DeleteDatabase(SQLiteDatabase db,String table) 
{ 


    db.execSQL("DELETE FROM " + table); 
    db.close(); 
} 

} 

Answer 1

Trudno odpowiedzieć bez dalszych kontekście, ale ostateczny kwerendy sqlite byłoby:

db.execSQL("DROP TABLE IF EXISTS tablename"); 

Gdzie db jest odwołaniem do obiektu SqliteDatabase.

i usuwać bazy danych

context.deleteDatabase(DATABASE_NAME); 

Answer 2

Poniższy kod usuwa tabele z DB:

db.execSQL("delete from " + DBNAME); 

Aby usunąć bazy danych:

myCtx.deleteDatabase(DATABASE_NAME); 

gdzie myCtx jest obecny kontekst, powinna ona nie może mieć wartości NULL.

Aby usunąć wiersz:

db.delete("'" + DBNAME+ "'", "Key" + "=" + rowID, null); 

Answer 3

SQLiteOpenHelper.getWritableDatabase może uzyskać klasę SQLiteDatabase, SQLiteDatabase.delete (String table, String whereClause, String[] whereArgs) możesz usuwać tabeli.

jeśli chcesz usunąć bazę danych, można skierowany usunąć plik bazy danych, ścieżkę:

/data/data/package_name/databases/db_name