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How to Delete Data in Back4App Database in Android?

  • Last Updated : 24 May, 2021

We have seen adding data to our Back4App database along with reading and updating this data. In this article, we will take a look at Deleting this data. 

What we are going to build? 

We will be adding a simple button inside our update screen where we were updating our data and inside that screen, we will be adding a new button for deleting the course. After deleting, that course will be deleted from our database. 

Step by Step Implementation

Step 1: Creating a new button for deleting the data inside the activity_update_course.xml file

As we have created a new Update Course Activity in the previous article. So we will simply add a new button to it. Add the following code snippet to the activity_update_course.xml file. 

XML






<!--button for deleting our course-->
<Button
  android:id="@+id/idBtnDelete"
  android:layout_width="0dp"
  android:layout_height="wrap_content"
  android:layout_margin="3dp"
  android:layout_weight="1"
  android:text="Delete Course"
  android:textAllCaps="false" />

Below is the updated code for the activity_update_course.xml file. 

XML




<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".UpdateCourseActivity">
 
    <!--Edit text for getting course Name-->
    <EditText
        android:id="@+id/idEdtCourseName"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="10dp"
        android:layout_marginTop="20dp"
        android:layout_marginEnd="10dp"
        android:hint="Course Name"
        android:importantForAutofill="no"
        android:inputType="text" />
 
    <!--Edittext for getting course Duration-->
    <EditText
        android:id="@+id/idEdtCourseDuration"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="10dp"
        android:layout_marginTop="20dp"
        android:layout_marginEnd="10dp"
        android:hint="Course Duration in min"
        android:importantForAutofill="no"
        android:inputType="time" />
 
    <!--Edittext for getting course Description-->
    <EditText
        android:id="@+id/idEdtCourseDescription"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="10dp"
        android:layout_marginTop="20dp"
        android:layout_marginEnd="10dp"
        android:hint="Course Description"
        android:importantForAutofill="no"
        android:inputType="text" />
 
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginStart="10dp"
        android:layout_marginTop="20dp"
        android:layout_marginEnd="10dp"
        android:orientation="horizontal"
        android:weightSum="2">
 
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginStart="10dp"
            android:layout_marginTop="20dp"
            android:layout_marginEnd="10dp"
            android:orientation="horizontal"
            android:weightSum="2">
 
            <!--button for updating our course-->
            <Button
                android:id="@+id/idBtnUpdate"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_margin="3dp"
                android:layout_weight="1"
                android:text="Update Course"
                android:textAllCaps="false" />
 
            <!--button for deleting our course-->
            <Button
                android:id="@+id/idBtnDelete"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_margin="3dp"
                android:layout_weight="1"
                android:text="Delete Course"
                android:textAllCaps="false" />
 
        </LinearLayout>
 
    </LinearLayout>
 
</LinearLayout>

Step 2: Now we have to initialize this button in the UpdateCourseActivity.java file and add onClickListener to it 

Go to the UpdateCourseActivity.java file and add the following code snippet.

Java




// Adding on click listener for delete button
deleteCourseBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // calling a method to delete a course.
                deleteCourse(originalCourseName);
        }
});
 
private void deleteCourse(String courseName) {
 
        // Configure Query with our query.
        ParseQuery<ParseObject> query = ParseQuery.getQuery("courses");
 
        // adding a condition where our course name
        // must be equal to the original course name
        query.whereEqualTo("courseName", courseName);
 
        // on below line we are finding the course with the course name.
        query.findInBackground(new FindCallback<ParseObject>() {
            @Override
            public void done(List<ParseObject> objects, ParseException e) {
                // if the error is null.
                if (e == null) {
                    // on below line we are getting the first course and
                    // calling a delete method to delete this course.
                    objects.get(0).deleteInBackground(new DeleteCallback() {
                        @Override
                        public void done(ParseException e) {
                            // inside done method checking if the error is null or not.
                            if (e == null) {
                                // if the error is not null then we are displaying a toast message and opening our home activity.
                                Toast.makeText(UpdateCourseActivity.this, "Course Deleted..", Toast.LENGTH_SHORT).show();
                                Intent i = new Intent(UpdateCourseActivity.this, HomeActivity.class);
                                startActivity(i);
                            } else {
                                // if we get error we are displaying it in below line.
                                Toast.makeText(UpdateCourseActivity.this, "Fail to delete course..", Toast.LENGTH_SHORT).show();
                            }
                        }
                    });
                } else {
                    // if we don't get the data in our database then we are displaying below message.
                    Toast.makeText(UpdateCourseActivity.this, "Fail to get the object..", Toast.LENGTH_SHORT).show();
                }
            }
     });
}

Below is the updated code for the UpdateCourseActivity.java file. 

Java




import android.content.Intent;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
 
import androidx.appcompat.app.AppCompatActivity;
 
import com.parse.DeleteCallback;
import com.parse.FindCallback;
import com.parse.GetCallback;
import com.parse.ParseException;
import com.parse.ParseObject;
import com.parse.ParseQuery;
import com.parse.SaveCallback;
 
import java.util.List;
 
public class UpdateCourseActivity extends AppCompatActivity {
 
    // creating variables for our edit text
    private EditText courseNameEdt, courseDurationEdt, courseDescriptionEdt;
 
    // creating variable for button
    private Button updateCourseBtn, deleteCourseBtn;
 
    // creating a strings for storing our values from edittext fields.
    private String courseName, courseDuration, courseDescription, originalCourseName, objectID;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_update_course);
 
        // initializing our edittext and buttons
        deleteCourseBtn = findViewById(R.id.idBtnDelete);
        updateCourseBtn = findViewById(R.id.idBtnUpdate);
        courseNameEdt = findViewById(R.id.idEdtCourseName);
        courseDescriptionEdt = findViewById(R.id.idEdtCourseDescription);
        courseDurationEdt = findViewById(R.id.idEdtCourseDuration);
 
        // on below line we are setting data to our edit text field.
        courseNameEdt.setText(getIntent().getStringExtra("courseName"));
        courseDescriptionEdt.setText(getIntent().getStringExtra("courseDescription"));
        courseDurationEdt.setText(getIntent().getStringExtra("courseDuration"));
        originalCourseName = getIntent().getStringExtra("courseName");
 
        // Adding on click listener for delete button
        deleteCourseBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // calling a method to delete a course.
                deleteCourse(originalCourseName);
            }
        });
 
        updateCourseBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                courseName = courseNameEdt.getText().toString();
                courseDescription = courseDescriptionEdt.getText().toString();
                courseDuration = courseDurationEdt.getText().toString();
                // validating the text fields if empty or not.
                if (TextUtils.isEmpty(courseName)) {
                    courseNameEdt.setError("Please enter Course Name");
                } else if (TextUtils.isEmpty(courseDescription)) {
                    courseDescriptionEdt.setError("Please enter Course Description");
                } else if (TextUtils.isEmpty(courseDuration)) {
                    courseDurationEdt.setError("Please enter Course Duration");
                } else {
                    // calling method to update data.
                    updateData(originalCourseName, courseName, courseDescription, courseDuration);
                }
            }
        });
    }
 
    private void deleteCourse(String courseName) {
 
        // Configure Query with our query.
        ParseQuery<ParseObject> query = ParseQuery.getQuery("courses");
 
        // adding a condition where our course name
        // must be equal to the original course name
        query.whereEqualTo("courseName", courseName);
 
        // on below line we are finding the course with the course name.
        query.findInBackground(new FindCallback<ParseObject>() {
            @Override
            public void done(List<ParseObject> objects, ParseException e) {
                // if the error is null.
                if (e == null) {
                    // on below line we are getting the first course and
                    // calling a delete method to delete this course.
                    objects.get(0).deleteInBackground(new DeleteCallback() {
                        @Override
                        public void done(ParseException e) {
                            // inside done method checking if the error is null or not.
                            if (e == null) {
                                // if the error is not null then we are displaying a toast message and opening our home activity.
                                Toast.makeText(UpdateCourseActivity.this, "Course Deleted..", Toast.LENGTH_SHORT).show();
                                Intent i = new Intent(UpdateCourseActivity.this, HomeActivity.class);
                                startActivity(i);
                            } else {
                                // if we get error we are displaying it in below line.
                                Toast.makeText(UpdateCourseActivity.this, "Fail to delete course..", Toast.LENGTH_SHORT).show();
                            }
                        }
                    });
                } else {
                    // if we don't get the data in our database then we are displaying below message.
                    Toast.makeText(UpdateCourseActivity.this, "Fail to get the object..", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
 
    private void updateData(String originalCourseName, String courseName, String courseDescription, String courseDuration) {
 
        // Configure Query with our query.
        ParseQuery<ParseObject> query = ParseQuery.getQuery("courses");
 
        // adding a condition where our course name must be equal to the original course name
        query.whereEqualTo("courseName", originalCourseName);
 
        // in below method we are getting the unique id
        // of the course which we have to make update.
        query.getFirstInBackground(new GetCallback<ParseObject>() {
            @Override
            public void done(ParseObject object, ParseException e) {
                // inside done method we check
                // if the error is null or not.
                if (e == null) {
 
                    // if the error is null then we are getting
                    // our object id in below line.
                    objectID = object.getObjectId().toString();
 
                    // after getting our object id we will
                    // move towards updating our course.
                    // calling below method to update our course.
                    query.getInBackground(objectID, new GetCallback<ParseObject>() {
                        @Override
                        public void done(ParseObject object, ParseException e) {
                            // in this method we are getting the
                            // object which we have to update.
                            if (e == null) {
 
                                // in below line we are adding new data
                                // to the object which we get from its id.
                                // on below line we are adding our data
                                // with their key value in our object.
                                object.put("courseName", courseName);
                                object.put("courseDescription", courseDescription);
                                object.put("courseDuration", courseDuration);
 
                                // after adding new data then we are
                                // calling a method to save this data
                                object.saveInBackground(new SaveCallback() {
                                    @Override
                                    public void done(ParseException e) {
                                        // inside on done method we are checking
                                        // if the error is null or not.
                                        if (e == null) {
                                            // if the error is null our data has been updated.
                                            // we are displaying a toast message and redirecting
                                            // our user to home activity where we are displaying course list.
                                            Toast.makeText(UpdateCourseActivity.this, "Course Updated..", Toast.LENGTH_SHORT).show();
                                            Intent i = new Intent(UpdateCourseActivity.this, HomeActivity.class);
                                            startActivity(i);
                                        } else {
                                            // below line is for error handling.
                                            Toast.makeText(UpdateCourseActivity.this, "Fail to update data " + e.getLocalizedMessage(), Toast.LENGTH_SHORT).show();
                                        }
                                    }
                                });
                            } else {
                                // on below line we are displaying a message
                                // if we don't get the object from its id.
                                Toast.makeText(UpdateCourseActivity.this, "Fail to update course " + e.getLocalizedMessage(), Toast.LENGTH_SHORT).show();
                            }
                        }
                    });
                } else {
                    // this is error handling if we don't get the id for our object
                    Toast.makeText(UpdateCourseActivity.this, "Fail to get object ID..", Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
}

Now run your app and see the output of the app. Make sure to add the course before performing this operation. 

Output:

Below is the file structure in Android Studio after performing the Delete operation:

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