SQLite：当插入工作正常时从查询中获取值 0

Question

我有一个 Table Notes (_Id, Title, Body, Category) 和一个 Table Categories (_Id, Name)，引用类别 Categories._Id。

通过这种方法，我在我的 SQLite 数据库中创建了一个注释。

/**
 * Create a new note using the title and body provided, and associated to
 * the category with row id provided. If the note is successfully created
 * return the new rowId for that note, otherwise return  a -1 to indicate failure.
 *
 * @param title the title of the note
 * @param body the body of the note
 * @param category the category associated to the note
 * @return rowId or -1 if failed
 */
public long createNote(String title, String body, String category) {
    if (title == null || title.equals("") || body == null) {
        return -1;
    }
    else {
        ContentValues initialValues = new ContentValues();
        initialValues.put(NOTE_KEY_TITLE, title);
        initialValues.put(NOTE_KEY_BODY, body);
        // If it has associated a category
        if (!category.equals("No Category")) {
            Cursor idCategory = fetchCategory(category);
            long catId = idCategory.getLong(idCategory.getColumnIndex("_id"));
            initialValues.put(NOTE_KEY_CAT, catId);
        // Else, it has no category
        } else {
            initialValues.put(NOTE_KEY_CAT, (Byte) null);
        }
        return mDb.insert(DATABASE_NOTE_TABLE, null, initialValues);
    }
}

有了这个，我得到了我数据库中的所有笔记。

/**
 * Return a Cursor over the list of all notes in the database
 *
 * @param mode - if TITLE, it returns the list ordered by the title of the notes.
 *             - if CATEGORY, it returns the list ordered by the category of the notes.
 *             - it returns null in another case.
 * @param category - category of the notes to return (No Category if none)
 * @return Cursor over all notes
 */
public Cursor fetchAllNotes(String mode, String category) {
    //// Order
    String order;
    // Mode is Title
    if (mode.equals("TITLE")) {
        order = NOTE_KEY_TITLE;
    // Mode is Categories
    } else if (mode.equals("CATEGORY")) {
        order = CAT_KEY_NAME;
    // A forbidden mode
    } else {
        return null;
    }
    // No category filter if it is No Category
    String cat;
    if (category.equals("No Category")) {
        cat = "";
    } else {
        cat = " WHERE " + CAT_KEY_NAME + "='" + category + "'";
    }                                     // Left outer because there are notes without category
    String query = "SELECT * FROM " + DATABASE_NOTE_TABLE + " LEFT OUTER JOIN " + DATABASE_CAT_TABLE +
            " C ON " + NOTE_KEY_CAT + "=C." + CAT_KEY_ROWID + cat + " ORDER BY " + order;
    return mDb.rawQuery(query, null);
}

编辑：

我实现了几个createNote()操作，并且注释被正确插入（方法returns创建的注释的正确rowId [1, 2, ...] ).
我意识到从fetchAllNotes()操作，所有的笔记都被返回了。但是，带有 No Category 的注释的 rowId 属性为 0（当 createNote() 返回正值时）。带有类别的注释具有正 rowId 值，但不正确。

例如：

CreateNote (Title: A, Body: B, Category: No Category). Returns 1
CreateNote (Title: C, Body: D, Category: No Category). Returns 2
CreateNote (Title: E, Body: F, Category: I have a Category). Returns 3

FetchAllNotes() Returns:

1. Note(0, A, B, No Category)
2. Note(0, C, D, No Category)
3. Note(1, E, F, I have a Category)`

知道发生了什么吗？

Answer 1

将 * 替换为完整的字段列表（这是最佳实践）。
所以要 return 只有 Cursor 中需要的字段。

SQLite：当插入工作正常时从查询中获取值 0

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