Error in searching a database for a particular record

Question

I have an SQLite database table called TABLE_CONTENTS made up of objects of type contact. Each contact has 2 variables: int id and String name. I want to search the SQLite database table for a specific id. For this I've made the isPresent() method in the class DatabaseHandler . It takes an int id and searches if an object with that id is present in the table and returns true or false accordingly.

The following code creates a database and adds 2 objects into it with ids 1 and 2 . It then tries to search for id=3 using isPresent() . This should return false causing the text id 3 is absent to show . However, it's returning true and the text displayed is id 3 is present .

What is wrong in this code? What is the correct code for isPresent()?

MainActivity.java

import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
import android.util.Log;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity
{

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

    DatabaseHandler db = new DatabaseHandler(this);

    // Inserting Contacts
    db.addContact(new Contact(1, "one"));
    db.addContact(new Contact(2, "two"));



    TextView text=(TextView) findViewById(R.id.text);
    text.setText(db.isPresent(3) ? "id 3 is present" : "id 3 is absent");


}

DatabaseHandler.java

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DatabaseHandler extends SQLiteOpenHelper
{
 private static final int DATABASE_VERSION=1;
 private static final String DATABASE_NAME="contactsManager";
 private static final String TABLE_CONTACTS="contacts";
 private static final String KEY_ID="id";
 private static final String KEY_NAME="name";

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

@Override
public void onCreate(SQLiteDatabase db)
{
    String CREATE_CONTACTS_TABLE="CREATE TABLE "+TABLE_CONTACTS+"("+KEY_ID+" INTEGER PRIMARY KEY, "+KEY_NAME+" TEXT "+")";
    db.execSQL(CREATE_CONTACTS_TABLE);
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion)
{
 db.execSQL("DROP TABLE IF EXISTS"+TABLE_CONTACTS);
    onCreate(db);
}

void addContact(Contact contact)
{
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put(KEY_NAME, contact.name);
    values.put(KEY_ID, contact.id);

    // Inserting Row
    db.insert(TABLE_CONTACTS, null, values);
    //2nd argument is String containing nullColumnHack
    db.close(); // Closing database connection
}


// not working properly..always returning true
public boolean isPresent(int id)
{
    SQLiteDatabase sqldb = this.getReadableDatabase();
    String Query = "Select * from " + TABLE_CONTACTS ;
    Cursor cursor = sqldb.rawQuery(Query, null);
    cursor.moveToLast(); //if you not place this cursor.getCount() always give same integer (1) or current position of cursor.

    if(cursor.getCount()<=0)
    {
        return false;
    }

    return true;
}




Contact getContact(int id)
{
    SQLiteDatabase db = this.getReadableDatabase();

    Cursor cursor = db.query(TABLE_CONTACTS, new String[] { KEY_ID,
                    KEY_NAME}, KEY_ID + "=?",
            new String[] { String.valueOf(id) }, null, null, null, null);
    if (cursor != null)
        cursor.moveToFirst();

    Contact contact = new Contact(Integer.parseInt(cursor.getString(0)),
            cursor.getString(1));
    // return contact
    return contact;
}

public int updateContact(Contact contact)
{
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put(KEY_NAME, contact.name);


    // updating row
    return db.update(TABLE_CONTACTS, values, KEY_ID + " = ?",
            new String[] { String.valueOf(contact.id) });
}


}






}

contact class

public class Contact
{
public String name;
public int id;

Contact(int id, String name)
{
    this.id=id;
    this.name=name;
}


}

Answer 1

Try,

As I see u haven't added any condition to select particular row. So, its just like get all not selected one. So, cursor.getCount() <= 0 is always false because u have added 2 records.

In isPresent(int id) method update the query as below and try once,

String Query = "Select * from " + TABLE_CONTACTS + " WHERE " + KEY_ID + "='"+ id + "'";

Answer 2

You haven't added any WHERE Clause in your query to search records according to id, therefore it always select all rows from your database which will always return count >0, so that's why your code is not working.

You have to modify your Select query to include WHERE clause in it something like this.

String yourQuery= "Select * from " + TABLE_CONTACTS + " WHERE " + KEY_ID + "='"+ id + "'";