java - 如何在 android SQLite 中的现有表上添加列？

Question

如何在现有表 LOGIN 中添加列。这是我的示例代码。

这是我的 DataBaseAdapter 类:

public class DataBaseHelper extends SQLiteOpenHelper
{
    public DataBaseHelper(Context context, String name,CursorFactory factory, int version) 
    {
               super(context, name, factory, version);
    }
    // Called when no database exists in disk and the helper class needs
    // to create a new one.
    @Override
    public void onCreate(SQLiteDatabase _db) 
    {
            _db.execSQL(LoginDataBaseAdapter.DATABASE_CREATE);

    }
    // Called when there is a database version mismatch meaning that the version
    // of the database on disk needs to be upgraded to the current version.
    @Override
    public void onUpgrade(SQLiteDatabase _db, int _oldVersion, int _newVersion) 
    {
            // Log the version upgrade.
            Log.w("TaskDBAdapter", "Upgrading from version " +_oldVersion + " to " +_newVersion + ", which will destroy all old data");


            // Upgrade the existing database to conform to the new version. Multiple
            // previous versions can be handled by comparing _oldVersion and _newVersion
            // values.
            // The simplest case is to drop the old table and create a new one.
            _db.execSQL("DROP TABLE IF EXISTS " + "TEMPLATE");
            // Create a new one.
            onCreate(_db);
    }

这是我的 LoginDataBaseAdapter

public class LoginDataBaseAdapter 
{
        static final String DATABASE_NAME = "login.db";
        static final int DATABASE_VERSION = 1;
        public static final int NAME_COLUMN = 1;
        // TODO: Create public field for each column in your table.
        // SQL Statement to create a new database.
        static final String DATABASE_CREATE = "create table "+"LOGIN"+
                                     "( " +"ID"+" integer primary key autoincrement,"+ "USERNAME  text,PASSWORD text); ";
        // Variable to hold the database instance
        public  SQLiteDatabase db;
        // Context of the application using the database.
        private final Context context;
        // Database open/upgrade helper
        private DataBaseHelper dbHelper;
        public  LoginDataBaseAdapter(Context _context) 
        {
            context = _context;
            dbHelper = new DataBaseHelper(context, DATABASE_NAME, null, DATABASE_VERSION);
        }
        public  LoginDataBaseAdapter open() throws SQLException 
        {
            db = dbHelper.getWritableDatabase();
            return this;
        }
        public void close() 
        {
            db.close();
        }

        public  SQLiteDatabase getDatabaseInstance()
        {
            return db;
        }

        public void insertEntry(String userName,String password)
        {
           ContentValues newValues = new ContentValues();
            // Assign values for each row.
            newValues.put("USERNAME", userName);
            newValues.put("PASSWORD",password);

            // Insert the row into your table
            db.insert("LOGIN", null, newValues);
            ///Toast.makeText(context, "Reminder Is Successfully Saved", Toast.LENGTH_LONG).show();
        }
        public int deleteEntry(String UserName)
        {
            //String id=String.valueOf(ID);
            String where="USERNAME=?";
            int numberOFEntriesDeleted= db.delete("LOGIN", where, new String[]{UserName}) ;
           // Toast.makeText(context, "Number fo Entry Deleted Successfully : "+numberOFEntriesDeleted, Toast.LENGTH_LONG).show();
            return numberOFEntriesDeleted;
        }   
        public String getSinlgeEntry(String userName1)
        {
            Cursor cursor=db.query("LOGIN", null, " USERNAME=?", new String[]{userName1}, null, null, null);
            if(cursor.getCount()<1) // UserName Not Exist
            {
                cursor.close();
                return "NOT EXIST";
            }
            cursor.moveToFirst();
            String password= cursor.getString(cursor.getColumnIndex("PASSWORD"));
            cursor.close();
            return password;                
        }
        public void  updateEntry(String userName,String password)
        {
            // Define the updated row content.
            ContentValues updatedValues = new ContentValues();
            // Assign values for each row.
            updatedValues.put("USERNAME", userName);
            updatedValues.put("PASSWORD",password);

            String where="USERNAME = ?";
            db.update("LOGIN",updatedValues, where, new String[]{userName});               
        }       
}

如何添加 FIRSTNAME(来自 TextView)、LASTNAME(来自 TextView)、DEPARTMENT(来自 Spinner)列。

Answer 1

如果您只想添加一列或多列，也可以更改现有表格。假设您想将名为“my_new_col”的新列添加到名为“my_table”的表中，除了将数据库版本号从 1 更新为 2 之外，您还可以更新表的架构而不会丢失任何数据:

...
@Override
public void onUpgrade( SQLiteDatabase db, int oldVersion, int newVersion ) {
    switch( newVersion ) {

        case 2: /* this is your new version number */

            // ... Add new column 'my_new_col' to table 'my_table'
            db.execSQL( "alter table my_table add column my_new_col" ) ;
            break ;
    }
}

就是这样。当然，您可能希望对该新列定义额外的约束，并且您希望确保新列包含在“onCreate(...)”中原始表的创建中。