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[英]can i dynamically add new column to sqlite table by calling a method from another class?
[英]Unable to add column dynamically into the sqlite table
logcat說出以下錯誤:
08-12 21:31:12.373: I/Database(325): sqlite returned: error code = 1, msg = near "10010325": syntax error
08-12 21:31:12.373: E/Database(325): Failure 1 (near "10010325": syntax error) on 0x2396b8 when preparing 'ALTER TABLE Student_attendance ADD COLUMN 10010325 INTEGER NOT NULL DEFAULT 0;'.
當學生創建一個新帳戶addcolumn
函數時,這是StudentLoginPage.java ,它應該向addcolumn
添加一個新列
case R.id.buttonRegister:
mStudentname = (EditText) findViewById(R.id.editStudentname);
mSPassword = (EditText) findViewById(R.id.editSPassword);
mSRollno = (EditText) findViewById(R.id.editRoll);
mSEmail = (EditText) findViewById(R.id.editEmail);
String uname = mStudentname.getText().toString();
String pass = mSPassword.getText().toString();
String roll = mSRollno.getText().toString();
String email = mSEmail.getText().toString();
boolean invalid = false;
if (uname.equals("")) {
invalid = true;
Toast.makeText(getApplicationContext(), "Username Missing",
Toast.LENGTH_SHORT).show();
} else if (pass.equals("")) {
invalid = true;
Toast.makeText(getApplicationContext(), "Password Missing",
Toast.LENGTH_SHORT).show();
} else if (roll.equals("")) {
invalid = true;
Toast.makeText(getApplicationContext(), "Roll no Missing",
Toast.LENGTH_SHORT).show();
} else if (email.equals("")) {
invalid = true;
Toast.makeText(getApplicationContext(), "Email ID Missing",
Toast.LENGTH_SHORT).show();
}
if (invalid == false) {
addEntry(uname, pass, roll, email);
addColumn(roll);
Intent i_register = new Intent(NewStudentPage.this,
MainActivity.class);
startActivity(i_register);
finish();
}
break;
}
}
private void addColumn(String roll) {
// TODO Auto-generated method stub
SQLiteDatabase db = myDb.getWritableDatabase();
try {
db.execSQL("ALTER TABLE "+ DbHelper.ATTENDANCE_TABLE +" ADD COLUMN "+ roll +" INTEGER NOT NULL DEFAULT 0;");
} catch (Exception e) {
// TODO: handle exception
}
}
這是DbHelper.java這里我創建了三個表STUDENT_TABLE,ATTENDANCE_TABLE和TEACHER_TABLE
public class DbHelper extends SQLiteOpenHelper {
private static final String DATABASE_NAME = "subh.db";
private static final int DATABASE_VERSION = 1;
public static final String ATTENDANCE_TABLE = "Student_attendance";
public static final String TEACHER_TABLE = "Teacher_login";
public static final String STUDENT_TABLE = "Student_login";
public static final String T_ROW_ID = "teacher_id";
private static final String ATTENDANCE_TABLE_CREATE = "CREATE TABLE "
+ ATTENDANCE_TABLE + "(" + "_id INTEGER PRIMARY KEY AUTOINCREMENT,"
+ "teacher_id INTEGER , " + "time TEXT NOT NULL); ";
private static final String TEACHER_TABLE_CREATE = "CREATE TABLE "
+ TEACHER_TABLE
+ "( teacher_id INTEGER PRIMARY KEY AUTOINCREMENT , "
+ "t_name TEXT NOT NULL , t_pass TEXT NOT NULL , t_email TEXT NOT NULL);";
private static final String STUDENT_TABLE_CREATE = "CREATE TABLE "
+ STUDENT_TABLE + "( s_id INTEGER PRIMARY KEY AUTOINCREMENT , "
+ "s_name TEXT NOT NULL , s_pass TEXT NOT NULL , "
+ "s_roll_no TEXT NOT NULL , " + "s_email TEXT NOT NULL);";
public DbHelper(Context context) {
super(context, DATABASE_NAME, null, DATABASE_VERSION);
System.out.println("In constructor");
}
@Override
public void onCreate(SQLiteDatabase db) {
// TODO Auto-generated method stub
try {
db.execSQL(TEACHER_TABLE_CREATE);
db.execSQL(ATTENDANCE_TABLE_CREATE);
db.execSQL(STUDENT_TABLE_CREATE);
System.out.println("In onCreate");
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
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");
db.execSQL("DROP TABLE IF EXISTS " + "TEMPLATE");
// Create a new one.
onCreate(db);
}
}
添加欄目10010325 ......
列名必須是有效的標識符 - 以10010325
開頭的字母數字,但列名稱的編號為10010325
- 這不起作用!
更新 :
動態添加列聽起來像災難的配方。 通過使用適當的數據庫模式,您將會更好,如下所示:
CREATE TABLE classes (
_id INTEGER PRIMARY KEY AUTOINCREMENT,
class_name VARCHAR(32),
teacher_id INTEGER,
time TEXT NOT NULL
);
然后創建這樣的考勤表:
CREATE TABLE student_attendance (
_id INTEGER PRIMARY KEY AUTOINCREMENT,
class_id INTEGER,
student_id INTEGER
);
表student_attendance
現在應該為每個參加課程的學生提供額外的行。 這樣,您就不必動態更改架構。
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