In the previous articles, we have seen three operations of CRUD operations such as create, read and update operations in our Android app. In this article, we will take a look at adding delete operation for deleting our items stored in the SQLite database.
What we are going to build in this article?
We will be building a simple application in which we will be deleting the course from our SQLite database in our Android app. A sample video is given below to get an idea about what we are going to do in this article.
Step by Step Implementation
Step 1: Updating our DBHandler class
As we have to delete data from our SQLite database. For that, we have to create a method to delete our data from the SQLite database. Navigate to the app > java > your app’s package name > DBHandler and add the below code to it.
Java
// below is the method for deleting our course.public void deleteCourse(String courseName) { // on below line we are creating // a variable to write our database. SQLiteDatabase db = this.getWritableDatabase(); // on below line we are calling a method to delete our // course and we are comparing it with our course name. db.delete(TABLE_NAME, "name=?", new String[]{courseName}); db.close();} |
Below is the updated code for the DBHandler.java file after adding the above code snippet.
Java
import android.content.ContentValues;import android.content.Context;import android.database.Cursor;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;import java.util.ArrayList;public class DBHandler extends SQLiteOpenHelper { // creating a constant variables for our database. // below variable is for our database name. private static final String DB_NAME = "coursedb"; // below int is our database version private static final int DB_VERSION = 1; // below variable is for our table name. private static final String TABLE_NAME = "mycourses"; // below variable is for our id column. private static final String ID_COL = "id"; // below variable is for our course name column private static final String NAME_COL = "name"; // below variable id for our course duration column. private static final String DURATION_COL = "duration"; // below variable for our course description column. private static final String DESCRIPTION_COL = "description"; // below variable is for our course tracks column. private static final String TRACKS_COL = "tracks"; // creating a constructor for our database handler. public DBHandler(Context context) { super(context, DB_NAME, null, DB_VERSION); } // below method is for creating a database by running a sqlite query @Override public void onCreate(SQLiteDatabase db) { // on below line we are creating // an sqlite query and we are // setting our column names // along with their data types. String query = "CREATE TABLE " + TABLE_NAME + " (" + ID_COL + " INTEGER PRIMARY KEY AUTOINCREMENT, " + NAME_COL + " TEXT," + DURATION_COL + " TEXT," + DESCRIPTION_COL + " TEXT," + TRACKS_COL + " TEXT)"; // at last we are calling a exec sql // method to execute above sql query db.execSQL(query); } // this method is use to add new course to our sqlite database. public void addNewCourse(String courseName, String courseDuration, String courseDescription, String courseTracks) { // on below line we are creating a variable for // our sqlite database and calling writable method // as we are writing data in our database. SQLiteDatabase db = this.getWritableDatabase(); // on below line we are creating a // variable for content values. ContentValues values = new ContentValues(); // on below line we are passing all values // along with its key and value pair. values.put(NAME_COL, courseName); values.put(DURATION_COL, courseDuration); values.put(DESCRIPTION_COL, courseDescription); values.put(TRACKS_COL, courseTracks); // after adding all values we are passing // content values to our table. db.insert(TABLE_NAME, null, values); // at last we are closing our // database after adding database. db.close(); } // we have created a new method for reading all the courses. public ArrayList<CourseModal> readCourses() { // on below line we are creating a // database for reading our database. SQLiteDatabase db = this.getReadableDatabase(); // on below line we are creating a cursor with query to read data from database. Cursor cursorCourses = db.rawQuery("SELECT * FROM " + TABLE_NAME, null); // on below line we are creating a new array list. ArrayList<CourseModal> courseModalArrayList = new ArrayList<>(); // moving our cursor to first position. if (cursorCourses.moveToFirst()) { do { // on below line we are adding the data from cursor to our array list. courseModalArrayList.add(new CourseModal(cursorCourses.getString(1), cursorCourses.getString(4), cursorCourses.getString(2), cursorCourses.getString(3))); } while (cursorCourses.moveToNext()); // moving our cursor to next. } // at last closing our cursor // and returning our array list. cursorCourses.close(); return courseModalArrayList; } // below is the method for updating our courses public void updateCourse(String originalCourseName, String courseName, String courseDescription, String courseTracks, String courseDuration) { // calling a method to get writable database. SQLiteDatabase db = this.getWritableDatabase(); ContentValues values = new ContentValues(); // on below line we are passing all values // along with its key and value pair. values.put(NAME_COL, courseName); values.put(DURATION_COL, courseDuration); values.put(DESCRIPTION_COL, courseDescription); values.put(TRACKS_COL, courseTracks); // on below line we are calling a update method to update our database and passing our values. // and we are comparing it with name of our course which is stored in original name variable. db.update(TABLE_NAME, values, "name=?", new String[]{originalCourseName}); db.close(); } // below is the method for deleting our course. public void deleteCourse(String courseName) { // on below line we are creating // a variable to write our database. SQLiteDatabase db = this.getWritableDatabase(); // on below line we are calling a method to delete our // course and we are comparing it with our course name. db.delete(TABLE_NAME, "name=?", new String[]{courseName}); db.close(); } @Override public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { // this method is called to check if the table exists already. db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME); onCreate(db); }} |
Step 2: Adding a button to delete our course
Navigate to the app > res > layout > activity_update_course.xml file and add a Button inside this layout for deleting a course. Below is the code for that file.
XML
<!--button for deleting our course--><Button android:id="@+id/idBtnDelete" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_margin="10dp" android:text="Delete Course" android:textAllCaps="false" /> |
Below is the updated code for the activity_update_course.xml file after adding the above code snippet.
XML
<?xml version="1.0" encoding="utf-8"?><LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" tools:context=".UpdateCourseActivity"> <!--Edit text to enter course name--> <EditText android:id="@+id/idEdtCourseName" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_margin="10dp" android:hint="Enter course Name" /> <!--edit text to enter course duration--> <EditText android:id="@+id/idEdtCourseDuration" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_margin="10dp" android:hint="Enter Course Duration" /> <!--edit text to display course tracks--> <EditText android:id="@+id/idEdtCourseTracks" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_margin="10dp" android:hint="Enter Course Tracks" /> <!--edit text for course description--> <EditText android:id="@+id/idEdtCourseDescription" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_margin="10dp" android:hint="Enter Course Description" /> <!--button for updating our course--> <Button android:id="@+id/idBtnUpdateCourse" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_margin="10dp" android:text="Update Course" android:textAllCaps="false" /> <!--button for deleting our course--> <Button android:id="@+id/idBtnDelete" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_margin="10dp" android:text="Delete Course" android:textAllCaps="false" /></LinearLayout> |
Step 3: Initializing our button to delete our course
Navigate to the app > java > your app’s package name > UpdateCourseActivity.java file and add the below code to it.
Java
// adding on click listener for delete button to delete our course.deleteCourseBtn.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { // calling a method to delete our course. dbHandler.deleteCourse(courseName); Toast.makeText(UpdateCourseActivity.this, "Deleted the course", Toast.LENGTH_SHORT).show(); Intent i = new Intent(UpdateCourseActivity.this, MainActivity.class); startActivity(i); }}); |
Below is the updated code for the UpdateCourseActivity.java file after adding the above code snippet.
Java
import android.content.Intent;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.EditText;import android.widget.Toast;import androidx.appcompat.app.AppCompatActivity;public class UpdateCourseActivity extends AppCompatActivity { // variables for our edit text, button, strings and dbhandler class. private EditText courseNameEdt, courseTracksEdt, courseDurationEdt, courseDescriptionEdt; private Button updateCourseBtn, deleteCourseBtn; private DBHandler dbHandler; String courseName, courseDesc, courseDuration, courseTracks; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_update_course); // initializing all our variables. courseNameEdt = findViewById(R.id.idEdtCourseName); courseTracksEdt = findViewById(R.id.idEdtCourseTracks); courseDurationEdt = findViewById(R.id.idEdtCourseDuration); courseDescriptionEdt = findViewById(R.id.idEdtCourseDescription); updateCourseBtn = findViewById(R.id.idBtnUpdateCourse); deleteCourseBtn = findViewById(R.id.idBtnDelete); // on below line we are initializing our dbhandler class. dbHandler = new DBHandler(UpdateCourseActivity.this); // on below lines we are getting data which // we passed in our adapter class. courseName = getIntent().getStringExtra("name"); courseDesc = getIntent().getStringExtra("description"); courseDuration = getIntent().getStringExtra("duration"); courseTracks = getIntent().getStringExtra("tracks"); // setting data to edit text // of our update activity. courseNameEdt.setText(courseName); courseDescriptionEdt.setText(courseDesc); courseTracksEdt.setText(courseTracks); courseDurationEdt.setText(courseDuration); // adding on click listener to our update course button. updateCourseBtn.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { // inside this method we are calling an update course // method and passing all our edit text values. dbHandler.updateCourse(courseName, courseNameEdt.getText().toString(), courseDescriptionEdt.getText().toString(), courseTracksEdt.getText().toString(), courseDurationEdt.getText().toString()); // displaying a toast message that our course has been updated. Toast.makeText(UpdateCourseActivity.this, "Course Updated..", Toast.LENGTH_SHORT).show(); // launching our main activity. Intent i = new Intent(UpdateCourseActivity.this, MainActivity.class); startActivity(i); } }); // adding on click listener for delete button to delete our course. deleteCourseBtn.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { // calling a method to delete our course. dbHandler.deleteCourse(courseName); Toast.makeText(UpdateCourseActivity.this, "Deleted the course", Toast.LENGTH_SHORT).show(); Intent i = new Intent(UpdateCourseActivity.this, MainActivity.class); startActivity(i); } }); }} |
Now run your app and see the output of the app. Make sure to add data to our database before deleting it.
Output:
Below is the complete project file structure after performing the delete operation:
