Android sqlite列未找到错误

Question

Ok so I have made the usual Database Helper class as shown below. I've also made a class which uses the getData and insertData methods with another class to get specific things, for example with my User class to get User name. However, when calling that Controller class in my main activity I want to use it in, it tells me that the columns I try access don't exist. I've been trying at this for hours now and am getting tired...

in logcat is says... sqlite returned:

error code = 1, msg = table userinfo has no column named username

Also I have added stuff like _id and android_metadata to my database. Thanks.

    public class DatabaseHelper extends SQLiteOpenHelper{

            //The Android's default system path of your application database.
            private static final String DB_PATH = "/data/data/com.cslearn/databases/";
            private static final String DB_NAME = "example.db";
            private static final int DB_VERSION = 1; 
            private final Context myContext;
            private SQLiteDatabase myDatabase;

            public DatabaseHelper(Context context) {
                super(context, DB_NAME, null, DB_VERSION);
                this.myContext = context;
                System.out.println(context.getDatabasePath("myDatabase"));
            }   
            public void createDataBase() throws IOException{
                System.out.println("database creating...");
                boolean dbExist = checkDataBase();

                if(dbExist){
                    //do nothing - database already exist
                    System.out.println("db exists");
                }else{
                    //By calling this method and empty database will be created into the default system path
                       //of your application so we are gonna be able to overwrite that database with our database.
                    this.getReadableDatabase();
                    System.out.println("path = "+this.getReadableDatabase().getPath());
                    System.out.println("get database");

                    try {
                        this.close();
                        copyDataBase(); 
                    } catch (IOException e) {
                        throw new Error("Error copying database");
                    }
                }
                System.out.println("database created");
                this.close();
            }
            private boolean checkDataBase(){

                SQLiteDatabase checkDB = null;

                try{
                    String myPath = DB_PATH + DB_NAME;
                    checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
                }catch(SQLiteException e){
                    //database does't exist yet.
                }

                if(checkDB != null){
                    checkDB.close();
                }
                return checkDB != null ? true : false;
            }
            private void copyDataBase() throws IOException{


                System.out.println("Copying database....");
                //Open your local db as the input stream
                InputStream myInput = myContext.getAssets().open(DB_NAME);
                System.out.println("input > get assets");
                // Path to the just created empty db
                String outFileName = DB_PATH + DB_NAME;

                //Open the empty db as the output stream
                OutputStream myOutput = new FileOutputStream(outFileName);

                //transfer bytes from the inputfile to the outputfile
                byte[] buffer = new byte[1024];
                int length;
                while ((length = myInput.read(buffer))>0){
                    myOutput.write(buffer, 0, length);
                    System.out.println("output write...");

                }
                System.out.println("Database copied!!");
                //Close the streams
                myOutput.flush();
                myOutput.close();
                myInput.close();

            }
         /**   public void openReadonlyDataBase() throws SQLException{

                //Open the database
                String myPath = DB_PATH + DB_NAME;
                myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

            }*/
            public void openDataBase() throws SQLException{
                String myPath = DB_PATH + DB_NAME;
                myDatabase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.NO_LOCALIZED_COLLATORS);
            }

            @Override
            public synchronized void close() {

                    if(myDatabase != null)
                        myDatabase.close();

                    super.close();
            }


            public void insertData (String sql){
                try {
                    this.createDataBase();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                try {
                    this.openDataBase();
                    System.out.println("database opened");
                }catch(SQLException e){

                    throw e;

                }
                myDatabase.execSQL(sql); //separate values with ,
                this.close();
            }



            public ArrayList<String> getData (String table,String [] columns, String selection){
                try {
                    this.createDataBase();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                try {
                    this.openDataBase();
                    System.out.println("database opened");

                }catch(SQLException e){
                    throw e;
                }
                System.out.println("getting data");
                ArrayList<String> results = new ArrayList<String>();
                Cursor c = myDatabase.query(table, columns, selection, null, null, null, null);
                System.out.println(c.getColumnCount());
                System.out.println(c.getColumnNames());
                System.out.println("got cursor c");     
                     if (c != null) {
                         /* Check if at least one Result was returned. */
                         if (c.moveToFirst()) {
                                 do {
                                         /* Retrieve the values of the Entry
                                          * the Cursor is pointing to. */
                                            String[] row = new String[c.getColumnCount()];      
                                            for(int i=0; i<c.getColumnCount(); i++){    
                                               row[i] = c.getString(i);
                                               System.out.println("getting data");
                                               results.add(row[i]);
                                               System.out.println("adding string");
                                    }

                                 } while (c.moveToNext());
                         }
                     }
                close();
                return results;
            }
            @Override
            public void onCreate(SQLiteDatabase db) {
            }
            @Override
            public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            }

                // Add your public helper methods to access and get content from the database.
               // You could return cursors by doing "return myDataBase.query(....)" so it'd be easy
               // to you to create adapters for your views.
}

Answer 1

You have overriden the onCreate(SQLiteDatabase db) method but it doesn't do anything. You need to create your tables in this method like so:

// SQL statements to create new tables.
private static final String TBL_FRIENDS = "friends";
private static final String CREATE_TABLE_FRIENDS = "create table " +
    TBL_FRIENDS + " (" + KEY_ID + " integer primary key autoincrement, " +
    FRIEND_ID + " integer not null, " + FRIEND_MARKER + " integer not null, " +
    FRIEND_MOBILE + " text not null, " + FRIEND_NAME + " text not null);";

@Override
    public void onCreate(SQLiteDatabase db)
    {           
        db.execSQL("DROP TABLE IF EXISTS " + TBL_FRIENDS);          
        db.execSQL(CREATE_TABLE_FRIENDS);           

    }

The other static strings shown eg KEY_ID are column names which are used in other methods.

Answer 2

You should put some code in onCreate() and onUpgrade() .

onCreate() is called when the database is created for the first time. onUpgrade() is called when the database version is increased.

Example use of onCreate() and onUpgrade()

• onCreate(SQLiteDatabase db) executes SQL commands that creates tables.
• onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) executes SQL commands that drops tables (if exists) then call onCreate() (so that the table will have the new structure).

Don't forget to increment DB_VERSION whenever you want to onUpgrade to be called.

Answer 3

您是否将DEFAULT VALUES分配给表的列名？