Question

我将故事名称称为 _TodayDate ，但每当数据发生变化时，表示不存在此类表格。

这是我的DatabaseHandler

昨天工作正常，但每当日期发生变化时，应用程序都会崩溃。

public class DatabaseHandler extends SQLiteOpenHelper {
    // All Static variables
    // Database Version    
    private static final int DATABASE_VERSION = 1; 
    // Database Name
    private static final String DATABASE_NAME = "entryManager";

    private static  String getTableName(){
        Calendar calendar = Calendar.getInstance();
        calendar.setTimeZone(TimeZone.getTimeZone("Asia/Calcutta"));
        SimpleDateFormat df = new SimpleDateFormat("yyyyMMdd");
        String date = "_"+df.format(calendar.getTime());
        return date; 
    }

    // Contacts table name
    private String TABLE_DATE = getTableName();
    //String formattedDate = DateFormat.getDateFormat().format(new Date());

    // Contacts Table Columns names
    private static final String KEY_ID = "id";
    private static final String KEY_ROLL = "Roll";
    private static final String KEY_DATE = "Date";
    private static final String KEY_TIME = "Time";

    public DatabaseHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String CREATE_ENTRY_TABLE = "CREATE TABLE " +TABLE_DATE + "("
                + KEY_ID + " INTEGER PRIMARY KEY," + KEY_ROLL + " TEXT,"
                + KEY_DATE + " TEXT," +  KEY_TIME + " TEXT" + ")";
        db.execSQL(CREATE_ENTRY_TABLE);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int i, int i1) {
        // Drop older table if existed
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_DATE);

        // Create tables again
        onCreate(db);
    }
    /**
     * All CRUD(Create, Read, Update, Delete) Operations
     */

    // Adding new contact
    void addEntry(EntryDetails entryDetails) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_ROLL, entryDetails.getRoll()); // ROll
        values.put(KEY_DATE, entryDetails.getDate()); // Date
        values.put(KEY_TIME, entryDetails.getTime()); //Time

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

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

        Cursor cursor = db.query(TABLE_DATE, new String[] { KEY_ID,
                        KEY_ROLL, KEY_DATE, KEY_TIME }, KEY_ID + "=?",
                new String[] { String.valueOf(id) }, null, null, null, null);
        if (cursor != null)
            cursor.moveToFirst();

        EntryDetails entryDetails = new EntryDetails(Integer.parseInt(cursor.getString(0)),
                cursor.getString(1), cursor.getString(2), cursor.getString(3));
        // return contact
        return entryDetails;
    }

    // Getting All Contacts
    public List<EntryDetails> getAllEntries() {
        List<EntryDetails> entryDetailses = new ArrayList<EntryDetails>();
        // Select All Query
        String selectQuery = "SELECT  * FROM " + TABLE_DATE;

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

        // looping through all rows and adding to list
        if (cursor.moveToFirst()) {
            do {
                EntryDetails entryDetails = new EntryDetails();
                entryDetails.set_id(Integer.parseInt(cursor.getString(0)));
                entryDetails.setRoll(cursor.getString(1));
                entryDetails.setDate(cursor.getString(2));
                entryDetails.setTime(cursor.getString(3));
                // Adding contact to list
                entryDetailses.add(entryDetails);
            } while (cursor.moveToNext());
        }

        // return contact list
        return entryDetailses;
    }

    // Updating single contact
    public int updateEntry(EntryDetails entryDetails) {
        SQLiteDatabase db = this.getWritableDatabase();

        ContentValues values = new ContentValues();
        values.put(KEY_ROLL, entryDetails.getRoll());
        values.put(KEY_DATE, entryDetails.getDate());
        values.put(KEY_TIME, entryDetails.getTime());

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

    // Deleting single contact
    public void deleteEntry(EntryDetails entryDetails) {
        SQLiteDatabase db = this.getWritableDatabase();
        db.delete(TABLE_DATE, KEY_ID + " = ?",
                new String[] { String.valueOf(entryDetails.get_id()) });
        db.close();
    }


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

        // return count
        return cursor.getCount();
    }
}

这是logcat。据说没有这样的表格。

    E/SQLiteLog: (1) no such table: _20180121
    01-21 00:31:32.078 7788-
    7788/com.jagdishchoudhary.iitgandhinagarmesssystem E/AndroidRuntime: 
    FATAL EXCEPTION: main

    Process: com.jagdishchoudhary.iitgandhinagarmesssystem, PID: 7788

    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.jagdishchoudhary.iitgandhinagarmesssystem/com.jagdishchoudhary.iitgandhinagarmesssystem.MainActivity}: android.database.sqlite.SQLiteException: no such table: _20180121 (code 1): , while compiling: SELECT  * FROM _20180121
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2659)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2724)
    at android.app.ActivityThread.-wrap12(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1473)
    at android.os.Handler.dispatchMessage(Handler.java:102)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6123)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:757)
 Caused by: android.database.sqlite.SQLiteException: no such table: _20180121 (code 1): , while compiling: SELECT  * FROM _20180121
    at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
    at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:889)
    at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:500)
    at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
    at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
    at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
    at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44)
    at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1318)
    at android.database.sqlite.SQLiteDatabase.rawQuery(SQLiteDatabase.java:1257)
    at com.jagdishchoudhary.iitgandhinagarmesssystem.DatabaseHandler.getAllEntries(DatabaseHandler.java:117)
    at com.jagdishchoudhary.iitgandhinagarmesssystem.MainActivity.onCreate(MainActivity.java:135)

Answer 1

根据您的经验，只要日期发生变化，表名就会发生变化。那是因为您将当前日期作为表名称。但是，不会创建这样的表，除非首次运行App，因为onCreate方法只会在创建数据库（表的容器）时运行，即它只运行一次。 / p>

正确的解决方案是不使用动态表名而是使用固定的表名。如果日期是一个重要因素，您应该在表格中有一个列的日期（如您所示），然后使用此列来区分数据。

如果您真的想要每个日期的表，那么您可以修改表定义以在IF NOT EXISTS方法中包含onCreate，然后在构造DatabaseHandeler时调用它。

所以你可以这样做： -

1）修改DatabaseHandler的onCreate方法，以便表定义包含IF NOT EXISTS： -

@Override
public void onCreate(SQLiteDatabase db) {
    String CREATE_ENTRY_TABLE = "CREATE TABLE IF NOT EXISTS " +TABLE_DATE + "("
            + KEY_ID + " INTEGER PRIMARY KEY," + KEY_ROLL + " TEXT,"
            + KEY_DATE + " TEXT," +  KEY_TIME + " TEXT" + ")";
    db.execSQL(CREATE_ENTRY_TABLE);
}

2）修改DatabaseHandler的构造函数以始终调用onCreate。： -

public DatabaseHandlerDates(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
    onCreate(this.getWritableDatabase()); //<<<< ADDED
}

<强>警告！关于使用多个/动态表格

onUpgrade方法是不够的，因为它只会DROP并重新创建当前日期的表。所有其他表都不会升级。（您可以通过从sqlite_master表中提取表列表来确定所有表。）
如果在使用应用程序时更改日期，您最终可能会在应用程序中使用2个表格，即您可能会收到意外结果。
除非受到管理，否则将存在越来越多的表。

另一种选择

您可以使用ALTER TABLE sql语句来RENAME表名。但是，您必须确定以前的表名才能重新命名（再次通过sqlite_master表进行拖网）。

处理表/数据将与建议的正确解决方案没有区别。除了在使用App时更改日期可能导致由于找不到表而导致崩溃（即任何新的DatabaseHandler实例，将使用新日期和ALTER表名，除非照顾（可能强制重启App））

SQLite数据库没有这样的表_20180121

1 个答案:

另一种选择