檢查數據庫android中是否存在記錄

Question

我想檢查SQLite數據庫中是否存在記錄，這是我到目前為止所做的。 當我搜索已經存在的記錄時，我從列表中的EditText獲取值。

    //code from activity class

    public View.OnClickListener searchStation = new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        arrayAdapterList=new ArrayAdapter<String>(SearchAndReview.this,
                android.R.layout.simple_list_item_1,
                list);
        String searchTextFinal=searchText.getText().toString();
        dbms.searchStation(searchTextFinal);
        Cursor cursor= dbms.searchStation(searchTextFinal);



       list.add(searchTextFinal);
        arrayAdapterList= new ArrayAdapter<String>(SearchAndReview.this,
                android.R.layout.simple_list_item_1, list);
        listView.setAdapter(arrayAdapterList);


    }
};

//來自databasehelper類的代碼

   public Cursor searchStation(String name){
    SQLiteDatabase database = this.getWritableDatabase();
    String searchStationQuery = "SELECT stationName FROM review WHERE stationId='"+ name+"'";
    Cursor c =database.rawQuery(searchStationQuery,null);
    if (c != null && c.moveToFirst()) {
    }
    return c;
}

Answer 1

我在我的應用程序中使用此代碼，它可以實現...

LoginActivity.java

DatabaseHelper dbHelper = new DatabaseHelper(getApplicationContext());
String email_id = email.getText().toString();
boolean dbHelper.isExist(email_id);

// if record is exist then it will return true otherwise this method returns false

使用rawQuery

 public boolean isExist(String strEmailAdd) {
        db = this.getReadableDatabase();
        cur = db.rawQuery("SELECT * FROM " + USER_TABLE + " WHERE email_id = '" + strEmailAdd + "'", null);
        boolean exist = (cur.getCount() > 0);
        cur.close();
        db.close();
        return exist;

    }

使用db.query

public boolean isExist(String strEmailAdd){

        String whereClause = "email_id = ?";
        String[] whereArgs = new String[]{strEmailAdd};

        db = database.getWritableDatabase();
        cur = db.query(USER_TABLE, null, whereClause, whereArgs, null, null, null);
        boolean exist = (cur.getCount() > 0);
        cur.close();
        db.close();
        return exist;
}

Answer 2

從表中選擇一行，是否得到結果=它存在，否則不存在。

public boolean doesStationExist(String name){
    final String query = "SELECT stationName FROM review WHERE stationId='"+name+"' LIMIT 1";
    try (SQLiteDatabase database = getReadableDatabase();
         Cursor c = database.rawQuery(query, null)) {
        return c.moveToFirst();
    }
}

順便說一下，從rawQuery返回的游標永遠不會為null 。

編輯：

一旦try塊完成，更新的代碼將關閉數據庫和光標。 這稱為try-with-resources。

Answer 3

DatabaseManager.java

public Cursor checkFavourites()
{

    String query="select * from "+DATABASE_TABLE;
    Cursor cursor=db.rawQuery(query,null);

    return cursor;
}

MainActivity.java

public void favourite_Click(View view){
    Cursor cursor=dbManager.checkFavourites();
    if (cursor.getCount()>0)
    {
        Toast.makeText(MainActivity.this, "Favourites", Toast.LENGTH_SHORT).show();
    }
    else
    {
        Toast.makeText(MainActivity.this,"Nothing in favourites yet", Toast.LENGTH_SHORT).show();
    }
}