Question

我试图清除＆＃39;文章＆＃39;中的所有条目。表，以防止重复数据...我已经尝试删除表，如果它已经存在，但是这不起作用，表没有被删除导致表中的重复条目..... < / p>

我试图清除表格中的所有条目＆＃39;文章＆＃39;在插入新数据之前......但我现在遇到的问题是，我在表格中仍然只有一个条目。应该有3个条目。

我试图清空这些文章＆＃39;表格开头是＆＃39; addArticle＆＃39;。

所以我试图： 1）删除文章表中的所有条目 2）向文章表添加新条目

请在下面编写代码：

public class SQLiteDatabaseHandler extends SQLiteOpenHelper {

    private static final int DATABASE_VERSION = 1;
    private static final String DATABASE_NAME = "mytubeDb";
    private static final String TABLE_NAME = "Articles";
    private static final String KEY_ID = "id";
    private static final String KEY_TITLE = "title";
    private static final String KEY_DESCRIPTION = "description";
    private static final String KEY_URL= "url";
    private static final String[] COLUMNS = { KEY_ID, KEY_TITLE, KEY_DESCRIPTION,
            KEY_URL };

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

    @Override
    public void onCreate(SQLiteDatabase db) {

        String CREATION_TABLE = "CREATE TABLE "+ TABLE_NAME +" ( "
                + "id INTEGER PRIMARY KEY AUTOINCREMENT, " + "title TEXT, "
                + "description TEXT, " + "url TEXT )";
        db.execSQL(CREATION_TABLE);


    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // you can implement here migration process
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        this.onCreate(db);
    }



    public Article getArticle(int id) {
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.query(TABLE_NAME, // a. table
                COLUMNS, // b. column names
                " id = ?", // c. selections
                new String[] { String.valueOf(id) }, // d. selections args
                null, // e. group by
                null, // f. having
                null, // g. order by
                null); // h. limit

        if (cursor != null)
            cursor.moveToFirst();


            Article article = new Article();
            article.setId(Integer.parseInt(cursor.getString(0)));
            article.setTitle(cursor.getString(1));
            article.setDescription(cursor.getString(2));
            article.setUrl(cursor.getString(3));

            return article;

    }

    public List<Article> allArticles() {

        List<Article> articles = new LinkedList<Article>();
        String query = "SELECT * FROM " + TABLE_NAME;
        SQLiteDatabase db = this.getWritableDatabase();
        Cursor cursor = db.rawQuery(query, null);
        Article article = null;

        if (cursor.moveToFirst()) {
            do {
                article = new Article();
                article.setId(Integer.parseInt(cursor.getString(0)));
                article.setTitle(cursor.getString(1));
                article.setDescription(cursor.getString(2));
                article.setUrl(cursor.getString(3));
                articles.add(article);
            } while (cursor.moveToNext());
        }

        return articles;
    }

    public void addArticle(Article article) {
        SQLiteDatabase db = this.getWritableDatabase();

        ///// TRYING TO CLEAR ALL RECORDS BEFORE ENTERING NEW ONES
        String Delete = "DELETE FROM " + TABLE_NAME;
        db.execSQL(Delete);


        values.put(KEY_TITLE, article.getTitle());
        values.put(KEY_DESCRIPTION, article.getDescription());
        values.put(KEY_URL, article.getUrl());
        // insert
        db.insert(TABLE_NAME,null, values);
        db.close();
    } ContentValues values = new ContentValues();



    }

活动

 private SQLiteDatabaseHandler db;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_journey_entertainment);


        db = new SQLiteDatabaseHandler(this);
        // create some players
        Article article1 = new Article(1, "THIS IS NEWS", "NEWS DESCRIPTION", "url1");
        Article article2 = new Article(2, "THIS IS MORE NEWS", "NEWS DESCRIPTION1", "url2");
        Article article3 = new Article(3, "EVEN MORE NEWS", "DESCRIPTION3", "url3");
        // add them
        db.addArticle(article1);
        db.addArticle(article2);
        db.addArticle(article3);


        // list all ARTICLES
        List<Article> articles = db.allArticles();

        if (articles != null) {
            String[] itemsTitle = new String[articles.size()];

            for (int i = 0; i < articles.size(); i++) {
                itemsTitle[i] = articles.get(i).toString();
            }

            // display like string instances
            ListView list = (ListView) findViewById(R.id.list);
            list.setAdapter(new ArrayAdapter<String>(this,
                    android.R.layout.simple_list_item_1, android.R.id.text1, itemsTitle));



        }

Answer 1

DELETE似乎不起作用的原因是由于逻辑而不是DELETE不起作用。每次调用/调用UIImageJPEGRepresentations方法然后添加1行时，都会从表中删除所有行。因此，您最终只能在表格中输入1行。

一种解决方案是在添加任何文章之前删除所有行，例如： -

addArticle

同时从db = new SQLiteDatabaseHandler(this); // delete all rows db.getWriteableDatabase().delete("Articles",null,null); //<<<<<<<< // create some players Article article1 = new Article(1, "THIS IS NEWS", "NEWS DESCRIPTION", "url1"); Article article2 = new Article(2, "THIS IS MORE NEWS", "NEWS DESCRIPTION1", "url2"); Article article3 = new Article(3, "EVEN MORE NEWS", "DESCRIPTION3", "url3"); // add them db.addArticle(article1); db.addArticle(article2); db.addArticle(article3);方法中移除行删除代码。

然后会是这样的： -

addArticle

另一种方法（假设您不是要更改要插入的数据）可能只是在表为空时调用public void addArticle(Article article) { SQLiteDatabase db = this.getWritableDatabase(); values.put(KEY_TITLE, article.getTitle()); values.put(KEY_DESCRIPTION, article.getDescription()); values.put(KEY_URL, article.getUrl()); // insert db.insert(TABLE_NAME,null, values); db.close(); }方法，同样从表中删除行删除代码addArticles方法，例如

e.g。你可以： -

addArticle

请注意！您可以通过删除App的数据来影响对数据的更改，这是清除表格的另一种方式（实际上完全删除了数据库）。

上面提到的db = new SQLiteDatabaseHandler(this); Article article1 = new Article(1, "THIS IS NEWS", "NEWS DESCRIPTION", "url1"); Article article2 = new Article(2, "THIS IS MORE NEWS", "NEWS DESCRIPTION1", "url2"); Article article3 = new Article(3, "EVEN MORE NEWS", "DESCRIPTION3", "url3"); if (DatabaseUtils.queryNumEntries(db.getWriteableDatabase(),"Articles") < 1) { // add them db.addArticle(article1); db.addArticle(article2); db.addArticle(article3); }是为了表示不明智，你可能会将这些陈述转移/转换为db.getWriteableDatabase()

内的方法

e.g。你可能有： -

SQLiteDatabaseHandler

如果你的最终目标是始终防止重复说文章的网址，那么你可以添加一个UNIQUE约束。

您可以使用： -

    public void deleteAllAtricles() {
        SQLiteDatabase db = this.getWriteableDatabase();
        db.delete(TABLE_NAME,null,null);
        db.close();
    }

    public long getArticleCount() {
        long rv;
        SQLiteDatabase db = this.getWriteableDatabase();
        rv = DatabaseUtils.queryNumEntries(db,TABLE_NAME);
        db.close();
        return rv;
    }

或

@Override
public void onCreate(SQLiteDatabase db) {

    String CREATION_TABLE = "CREATE TABLE "+ TABLE_NAME +" ( "
            + "id INTEGER PRIMARY KEY AUTOINCREMENT, " + "title TEXT, "
            + "description TEXT, " + "url TEXT UNIQUE )";
    db.execSQL(CREATION_TABLE);
}

微妙的区别在于，在前者中，唯一约束在列中定义，而后者在表级定义约束（这需要告知哪些列）。

如果有重复，则@Override public void onCreate(SQLiteDatabase db) { String CREATION_TABLE = "CREATE TABLE "+ TABLE_NAME +" ( " + "id INTEGER PRIMARY KEY AUTOINCREMENT, " + "title TEXT, " + "description TEXT, " + "url TEXT, UNIQUE(url)) "; db.execSQL(CREATION_TABLE); }将返回-1作为long（否则返回rowid，因为您有db.insert(TABLE_NAME,null, values);，id是rowid的别名）。您可能还希望按照SQLite Autoincrement 对AUTOINCREMENT进行操作，而只需编写代码id INTEGER PRIMARY KEY AUTOINCREMENT。

如何在添加新数据之前清除SQLite表中的所有条目？

1 个答案: