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:android="http://schemas.android.com/apk/res/android" 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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