Question

我在android sqlite中创建了一个简单的数据库表，其中我最初插入了一些记录，但问题是每次运行应用程序时，都会再次插入整个记录列表。例如，当我第一次运行应用程序数据库表时，我已经在我的表中插入了3条记录：

类别1-主题1-数据类别2-主题2-数据类别3-主题3-数据

现在，如果我在不插入任何新记录的情况下运行此应用程序，则数据库表将如下所示：类别1-主题1-数据类别2-主题2-数据类别3-主题3-数据类别1-主题1-数据类别2-主题2-数据类别3-主题3-数据

我该如何防止这种情况？请帮忙，真的很紧急。

这是我的代码：

DataColumns.java：

public class DataColumns {


 String KEY_CATEGORY = "_category";
String KEY_TOPIC  = "_topic";
  String KEY_DATA= "_datatoshow";


   public DataColumns() {}
    // TODO Auto-generated constructor stub

    public DataColumns(String _CAT, String _TOPIC, String _DATA)
    {
        this.KEY_CATEGORY = _CAT;
        this.KEY_TOPIC= _TOPIC;
        this.KEY_DATA = _DATA;
    }

    public DataColumns(String topic, String data)
    {

        this.KEY_TOPIC = topic;
        this.KEY_DATA = data;
    }


    public String getCATEGORY()
    {
        return this.KEY_CATEGORY;
    }

    public void setCATEGORY(String _cat)
    {
        this.KEY_CATEGORY = _cat;
    }

    public String getTOPIC()
    {
        return this.KEY_TOPIC;
    }

    public void setTOPIC(String topic)
    {
        this.KEY_TOPIC = topic;
    }

    public String getDATA()
    {
        return this.KEY_DATA;
    }

    public void setDATA(String data)
    {
        this.KEY_TOPIC = data;
    }

}

DataBaseHandler.java：

public class DataBaseHandler extends SQLiteOpenHelper {


    public static final String KEY_CATEGORY = "_CATEGORY";
    public static final String KEY_TOPIC = "_TOPIC";
    public static final String KEY_DATA = "_DATA";

     public static final String SQLITE_TABLE = "DB_TABLE";


        private static final String DATABASE_NAME = "WMCPROJECT.db";
        private static final int DATABASE_VERSION = 1;

    public DataBaseHandler(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        // TODO Auto-generated constructor stub
    }

        @Override
        public void onCreate(SQLiteDatabase db) {
            // TODO Auto-generated method stub

            db.execSQL("CREATE TABLE " + SQLITE_TABLE + "(" + _ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + KEY_CATEGORY + " TEXT NOT NULL, " + KEY_TOPIC + " TEXT NOT NULL,"  + KEY_DATA + " TEXT NOT NULL);");
            Log.d("db", "DATABASE CREATION"); 

        }
        @Override
        public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
            // TODO Auto-generated method stub

             // Drop older table if existed
            db.execSQL("DROP TABLE IF EXISTS " + SQLITE_TABLE);

            // Create tables again
            onCreate(db);

        }


    void    addRecord( DataColumns col_values)
        {
         SQLiteDatabase db = this.getWritableDatabase();

            ContentValues values = new ContentValues();

            values.put(KEY_CATEGORY,col_values.getCATEGORY()); 
            values.put(KEY_TOPIC, col_values.getTOPIC());
            values.put(KEY_DATA, col_values.getDATA());
            // Inserting Row
            db.insertOrThrow(SQLITE_TABLE, null, values);
            db.close(); // Closing database connection


        }

}

MainActivity.java：

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

 DataBaseHandler dbhandler = new DataBaseHandler(this);

 dbhandler.addRecord(new DataColumns("CAT1","TOPIC 1","data to show");
 dbhandler.addRecord(new DataColumns("CAT2","TOPIC 2","data to show");
 dbhandler.addRecord(new DataColumns("CAT3","TOPIC 3","data to show");



    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

}

Answer 1

尝试这样的事情......

void addRecord( DataColumns col_values)
        {
        SQLiteDatabase db = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(KEY_CATEGORY,col_values.getCATEGORY()); 
        values.put(KEY_TOPIC, col_values.getTOPIC());
        values.put(KEY_DATA, col_values.getDATA());

                String sqlQuery = "SELECT * FROM " + TABLENAME + " WHERE " + KEY_CATEGORY + " = " + "\""
                        + col_values.getCATEGORY() + "\"";

                Cursor c = db.rawQuery(sqlQuery, null);
                if (c != null && c.getCount() != 0) {

                } else {
                    db.insert(TABLENAME, null, values);
                }
  }

Answer 2

只需在onCreate方法中调用addRecord，就可以在onCreate方法中的DatabaseHandler类中调用它，如下所示：

        @Override
        public void onCreate(SQLiteDatabase db) {
            // TODO Auto-generated method stub

            db.execSQL("CREATE TABLE " + SQLITE_TABLE + "(" + _ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + KEY_CATEGORY + " TEXT NOT NULL, " + KEY_TOPIC + " TEXT NOT NULL,"  + KEY_DATA + " TEXT NOT NULL);");
            Log.d("db", "DATABASE CREATION"); 
            addRecord(new DataColumns("CAT1","TOPIC 1","data to show");
            addRecord(new DataColumns("CAT2","TOPIC 2","data to show");
            addRecord(new DataColumns("CAT3","TOPIC 3","data to show");
        }

SQLiteOpenHelper中的onCreate方法仅在第一次创建数据库时运行。

Answer 3

我测试了你的项目，我发现了一个问题。你必须在DataBaseHandler类的onCreate中使用db参数才能第一次添加。将DataBaseHandler中的onCreate方法更改为：

@Override
public void onCreate(SQLiteDatabase db) {
    // TODO Auto-generated method stub

    db.execSQL("CREATE TABLE " + SQLITE_TABLE
            + "(_id INTEGER PRIMARY KEY AUTOINCREMENT, " + KEY_CATEGORY
            + " TEXT NOT NULL, " + KEY_TOPIC + " TEXT NOT NULL," + KEY_DATA
            + " TEXT NOT NULL);");
    Log.d("db", "DATABASE CREATION");
    ContentValues cv = new ContentValues();
    cv.put(KEY_CATEGORY, "CAT1");
    cv.put(KEY_TOPIC, "TOPIC 1");
    cv.put(KEY_DATA, "data to show");
    db.insert(SQLITE_TABLE, null, cv);

    cv = new ContentValues();
    cv.put(KEY_CATEGORY, "CAT2");
    cv.put(KEY_TOPIC, "TOPIC 2");
    cv.put(KEY_DATA, "data to show");
    db.insert(SQLITE_TABLE, null, cv);

    cv = new ContentValues();
    cv.put(KEY_CATEGORY, "CAT3");
    cv.put(KEY_TOPIC, "TOPIC 3");
    cv.put(KEY_DATA, "data to show");
    db.insert(SQLITE_TABLE, null, cv);

}

我已经测试过它并且工作正常。

Android Sqlite重复插入

3 个答案: