java - Android studio SQL找不到表

Question

这个问题已经有答案了:

When does SQLiteOpenHelper onCreate() / onUpgrade() run? (15 个回答)

已关闭 5 年前。

我正在使用SQLiteDatabase我遇到了一个奇怪的问题 - 当我尝试SELECT * FROM时表给了我这个:

no such table: test_table (code 1): , while compiling: SELECT * FROM test_table

但是当我插入同一个表时，没有 Exception已发送。这是我的代码:

从表中获取所有数据的方法:

public List<Test> GetAllTests()
{
    List<Test> tests =new ArrayList<Test>();

    SQLiteDatabase db = this.getReadableDatabase();

    String sql = "SELECT * FROM " + TEST_TABLE;

    Cursor cursor = db.rawQuery(sql,null);
    if(cursor.moveToFirst())
    {
        do
        {
            Test test = new Test();
            test.setId(cursor.getInt(cursor.getColumnIndex(KEY_ID)));
            test.setSubjectID(cursor.getInt(cursor.getColumnIndex(KEY_SUBJECT_ID)));

            String dateString = cursor.getString(cursor.getColumnIndex(KEY_TEST_DATE));
            DateFormat format = new SimpleDateFormat("MMMM d, yyyy", Locale.ENGLISH);
            Date date = null;
            try {
                date = format.parse(dateString);
            } catch (ParseException e) {
                e.printStackTrace();
            }
            test.setDate(date);
            test.setGrade(cursor.getDouble(cursor.getColumnIndex(KEY_TEST_GRADE)));

            tests.add(test);
        }while(cursor.moveToNext());
    }
    return tests;
}

向同一个表插入数据的方法(无异常):

public long InsertTest(Test test)
{
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put(KEY_SUBJECT_ID,test.getSubjectID());
    values.put(KEY_TEST_DATE,test.getDate().toString());
    return db.insert(TEST_TABLE,null,values);
}

插入和获取数据的代码:

Test test = new Test(testSubjectID.getSelectedItemPosition(),date);
AddTestToList(test);
try {
    dbManager.InsertTest(test);
    List<Test> tests = dbManager.GetAllTests();
    for (Test test:tests)
    {
        AddTestToList(test);
    }
}catch (Exception e){Log.d("MSG_ERROR",e.toString());}

Answer 1

仅供引用

• 应用程序卸载不是一个好方法。如果您的应用位于 PLAYSTORE 上，那么？

您应该使用onUpgrade以避免数据丢失。

Called when the database needs to be upgraded. The implementation should use this method to drop tables, add tables, or do anything else it needs to upgrade to the new schema version.

如何？

@Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        Log.e(TAG, "Updating table from " + oldVersion + " to " + newVersion);


        if (oldVersion < 3){ // Here I SET 3. You should use your DB version . When-ever **`adding table`**  please increase DB version .
            db.execSQL(ALTER_USER_TABLE_1);
            db.execSQL(ALTER_USER_TABLE_2);
        }

    }

更改表

private static final String ALTER_USER_TABLE_1 =  "ALTER TABLE test_table ADD FIELD_NAME TEXT";
private static final String ALTER_USER_TABLE_2 = "ALTER TABLE test_table ADD FIELD_NAME2 TEXT";