java - 如何使用主键查找数据库中的行号(Android SQLite Eclipse Java)

Question

我在 ListView 中显示了一系列的 SQLite 条目，并且它们的主键位于并行数组中。当用户选择某个项目时，该项目将被发送到编辑器 Activity (以便用户可以编辑该条目)。按照我编程的方式，编辑器 Activity 类使用 Cursor 的 moveToPosition 函数，使用其行号(表示位置)从数据库中检索条目。

如何使用条目的主键来查找其行号？

编辑:
我找到了一个解决方案，其中我首先从数据库中检索选定的条目，然后返回并检索这些条目的主键。我将条目存储在一个数组中，将主键存储在另一个数组中。

希望您在看到代码后能够给出更清晰的答复。我正在寻找一种更优雅的解决方案，尽管这似乎可行。

这是相关代码。

CalendarMenu.java

@Override
public void onCreate(Bundle savedInstance){
  incomeManager = new SQLManagerIncome(this);
incomeManager.open();

  //This method (see below) gets all of the SQLite entries between two dates
    incomeArray = incomeManager.getDatedEntriesString(
            currentDay.getTimeInMillis(), 
              nextDay.getTimeInMillis());

  //This method (see below) gets the primary keys of all the entries retrieved 
  //in the previous method

    incomeArrayKeys = incomeManager.getDatedKeys(
           currentDay.getTimeInMillis(),
            nextDay.getTimeInMillis());
    incomeManager.close();

    // Sending the SQL info to the ListViews
    incomeAdapter = new ArrayAdapter<String>(this,
            android.R.layout.simple_list_item_1, incomeArray);
    dayList.setAdapter(incomeAdapter);
}


    @Override
public void onItemClick(AdapterView<?> listView, View view, int pos, long id) {
    Bundle basket = new Bundle();
    // we need to send the position of an entry inside the entire database to the
    // Editor class. So we'll use the primary key of an entry to retrieve its position.

    switch (listView.getId()) {
    case R.id.dayList:
        int entryPos = 0;
        //incomeArrayKeys holds all of the primary keys. It is a parallel
        //array to the array that is displayed in the listview 
        //(using a standard ArrayAdapter)
            incomeManager.open();
            entryPos = incomeManager.findPosByKey(incomeArrayKeys[pos]);
            incomeManager.close();

        basket.putLong("index", entryPos);
                    Class dayClass;
            try {
                dayClass = Class.forName("com.shulim.maaser.EditIncome");
                Intent dayIntent = new Intent(CalendarMenu.this, dayClass);
                dayIntent.putExtras(basket);
                startActivityForResult(dayIntent, 0);
            } catch (ClassNotFoundException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        break;
}

SQLManagerIncome.java

public String[] getDatedEntriesString(Long firstDay, Long lastDay){
    String[] columns = new String[] { KEY_ROWID, KEY_DESCRIPTION,
            KEY_AMOUNT, KEY_DATE, KEY_OWED };
    String selection = KEY_DATE + " >=" + firstDay + " AND " + KEY_DATE
            + "<" + lastDay;
    Cursor c = ourDatabase.query(INCOME_TABLE, columns, selection, null, null, null, null);
    int iDescription = c.getColumnIndex(KEY_DESCRIPTION);
    int iAmount = c.getColumnIndex(KEY_AMOUNT);
    ArrayList<String> keys = new ArrayList<String>();

    for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
        Long dateMillis = c.getLong(3);
        final Calendar cal = Calendar.getInstance();
        cal.setTimeInMillis(dateMillis);
        int mYear = cal.get(Calendar.YEAR);
        int mMonth = cal.get(Calendar.MONTH)+1;
        int mDay = cal.get(Calendar.DAY_OF_MONTH);
        String date = mMonth + "-" + mDay + "-" + mYear;
        String result = "Desc: " + c.getString(iDescription) 
                + ". Amount: $"
                + c.getString(iAmount) + ". Date: "
                + date + "\n";
        keys.add(result);
    }
    String[] stringDateKeys = new String[keys.size()];
    stringDateKeys = keys.toArray(stringDateKeys);
    c.close();
    return stringDateKeys;
}

public Integer[] getDatedKeys(Long firstDay, Long lastDay) {
    String[] columns = new String[] { KEY_ROWID, KEY_DESCRIPTION,
             KEY_AMOUNT, KEY_DATE };
    String selection = KEY_DATE + " >=" + firstDay + " AND " + KEY_DATE
            + "<" + lastDay;
    Cursor c = ourDatabase.query(INCOME_TABLE, columns, selection, null,
            null, null, null);
    int iRow = c.getColumnIndex(KEY_ROWID);
    ArrayList<Integer> keys = new ArrayList<Integer>();

    for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
        int result = c.getInt(iRow);
        keys.add(result);
    }

        Integer[] intKeys = new Integer[keys.size()];
        intKeys = keys.toArray(intKeys);
        c.close();
        return intKeys;
}

public int findPosByKey(Integer integer) {
    String[] columns = new String[] { KEY_ROWID, KEY_DESCRIPTION,
            KEY_AMOUNT, KEY_DATE };
    Cursor c = ourDatabase.query(INCOME_TABLE, columns, null, null,
            null, null, null);
    int iRow = c.getColumnIndex(KEY_ROWID);
    int position = 0;
    for (c.moveToFirst(); !c.isAfterLast(); c.moveToNext()) {
        if (c.getInt(iRow) == integer) {
            break;
        }
        position++;
    }
    c.close();
    return position;
}   

Answer 1

The way I programmed it, the Editor activity class retrieves the entry from the database using its row number (meaning position), using the Cursor's moveToPosition function.

您不需要使用光标的 moveToPosition 函数。相反，有一个更好的解决方案:使用您已有的主键。主键允许非常简单且高效的 SQL 查询，该查询将仅返回您想要的确切行。我不知道你的列名，但加载该行的 SQL 查询示例是

SELECT foo, bar, baz
FROM FooBar
WHERE pk = userSelectedPrimaryKey;

其中 userSelectedPrimaryKey 通过查询生成器插入到语句中。

当然，这只是一个粗略的草图，但要点是该查询将恰好返回一行，这是唯一具有用户选择的主键值的行。这更简单，并且提高了性能，因为不需要迭代不必要的行。