How to Delete Data in SQLite Database in Android using Jetpack Compose?

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 the delete operation for deleting our items stored in the SQLite database in the android application using Jetpack Compose.

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 using Jetpack Compose. 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. Comments are added in the code to get to know in detail. 

Kotlin

package com.example.newcanaryproject

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

// creating a constructor
// for our database handler
class DBHandler
    (context: Context?) :
    SQLiteOpenHelper(context, DB_NAME, null, DB_VERSION) {
    // below method is for creating a database
    // by running a sqlite query
    override fun onCreate(db: SQLiteDatabase) {
        // on below line we are creating
        // an sqlite query and we are
        // setting our column names
        // along with their data types.
        val 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.
    fun addNewCourse(
        courseName: String?,
        courseDuration: String?,
        courseDescription: String?,
        courseTracks: String?
    ) {

        // on below line we are creating a variable for
        // our sqlite database and calling writable method
        // as we are writing data in our database.
        val db = this.writableDatabase

        // on below line we are creating a
        // variable for content values.
        val values = 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()
    }

    override fun onUpgrade(db: SQLiteDatabase, oldVersion: Int, newVersion: Int) {
        // this method is called to check if the table exists already.
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME)
        onCreate(db)
    }

    companion object {
        // creating a constant variables for our database.
        // below variable is for our database name.
        private const val DB_NAME = "coursedb"

        // below int is our database version
        private const val DB_VERSION = 1

        // below variable is for our table name.
        private const val TABLE_NAME = "mycourses"

        // below variable is for our id column.
        private const val ID_COL = "id"

        // below variable is for our course name column
        private const val NAME_COL = "name"

        // below variable id for our course duration column.
        private const val DURATION_COL = "duration"

        // below variable for our course description column.
        private const val DESCRIPTION_COL = "description"

        // below variable is for our course tracks column.
        private const val TRACKS_COL = "tracks"
    }

    // we have created a new method for reading all the courses.
    fun readCourses(): ArrayList<CourseModal>? {
        // on below line we are creating a
        // database for reading our database.
        val db = this.readableDatabase

        // on below line we are creating a cursor
        // with query to read data from database.
        val cursorCourses: Cursor = db.rawQuery("SELECT * FROM $TABLE_NAME", null)

        // on below line we are creating a new array list.
        val courseModalArrayList: ArrayList<CourseModal> = 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(
                    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
    fun updateCourse(
        originalCourseName: String, courseName: String?, courseDescription: String?,
        courseTracks: String?, courseDuration: String?
    ) {

        // calling a method to get writable database.
        val db = this.writableDatabase
        val values = 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=?", arrayOf(originalCourseName))
        db.close()
    }

    // on below line creating a function to delete course
    fun deleteCourse(courseName: String) {
        // on below line we are creating
        // a variable to write our database.
        val db = this.writableDatabase

        // 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=?", arrayOf(courseName))
        db.close()
    }
}

Step 2: Adding a button in ViewCourses.kt file for deleting the course

Navigate to app>java>your app’s package name>ViewCourses.kt file and add the below code to it. Comments are added in the code to get to know in detail. 

Kotlin

package com.example.newcanaryproject

import android.content.Context
import android.content.Intent
import android.os.Bundle
import android.widget.Toast
import androidx.activity.ComponentActivity
import androidx.activity.compose.setContent
import androidx.compose.foundation.layout.*
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.itemsIndexed
import androidx.compose.material.*
import androidx.compose.runtime.Composable
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.platform.LocalContext
import androidx.compose.ui.text.style.TextAlign
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp
import com.example.newcanaryproject.ui.theme.NewCanaryProjectTheme
import com.example.newcanaryproject.ui.theme.greenColor

class ViewCourses : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            NewCanaryProjectTheme {
                // on below line we are specifying
                // background color for our application
                Surface(
                    // on below line we are specifying
                      // modifier and color for our app
                    modifier = Modifier.fillMaxSize(), color = MaterialTheme.colors.background
                ) {

                    // on the below line we are specifying
                      // the theme as the scaffold.
                    Scaffold(

                        // in scaffold we are specifying the top bar.
                        topBar = {

                            // inside top bar we are specifying
                              // background color.
                            TopAppBar(backgroundColor = greenColor,

                                // along with that we are specifying
                                // title for our top bar.
                                title = {

                                    // in the top bar we are
                                      // specifying tile as a text
                                    Text(
                                        // on below line we are specifying
                                        // text to display in top app bar.
                                        text = "GFG",

                                        // on below line we are specifying
                                        // modifier to fill max width.
                                        modifier = Modifier.fillMaxWidth(),

                                        // on below line we are specifying
                                        // text alignment.
                                        textAlign = TextAlign.Center,

                                        // on below line we are specifying
                                        // color for our text.
                                        color = Color.White
                                    )
                                })
                        }) {
                        // on below line we are calling our
                          // method to display UI
                        readDataFromDatabase(LocalContext.current)
                    }
                }
            }
        }
    }
}

@OptIn(ExperimentalMaterialApi::class)
@Composable
fun readDataFromDatabase(context: Context) {
    // on below line we are creating and
    // initializing our array list
    lateinit var courseList: List<CourseModal>
    courseList = ArrayList<CourseModal>()

    val dbHandler: DBHandler = DBHandler(context);
    courseList = dbHandler.readCourses()!!

    // on below line we are creating a
    // lazy column for displaying a list view.
    LazyColumn {
        // on below line we are setting data
          // for each item of our listview.
        itemsIndexed(courseList) { index, item ->
            // on below line we are creating a
              // card for our list view item.
            Card(
                // we are adding on click for
                  // each item of our grid view.
                onClick = {
                    val i = Intent(context, UpdateCourse::class.java)
                    i.putExtra("courseName", courseList[index].courseName)
                    i.putExtra("courseDuration", courseList[index].courseDuration)
                    i.putExtra("courseTracks", courseList[index].courseTracks)
                    i.putExtra("courseDescription", courseList[index].courseDescription)
                    context.startActivity(i)
                },
                // on below line we are adding
                // padding from our all sides.
                modifier = Modifier.padding(8.dp),

                // on below line we are adding
                // elevation for the card.
                elevation = 6.dp
            )
            {
                // on below line we are creating
                // a row for our list view item.
                Column(
                    // for our row we are adding modifier
                    // to set padding from all sides.
                    modifier = Modifier
                        .padding(8.dp)
                        .fillMaxWidth(),
                    horizontalAlignment = Alignment.Start,
                    verticalArrangement = Arrangement.Center
                ) {
                    // on the below line we are creating a text.
                    Text(
                        // inside the text on below line we are
                        // setting text as the language name
                        // from our modal class.
                        text = courseList[index].courseName,

                        // on below line we are adding padding
                        // for our text from all sides.
                        modifier = Modifier.padding(4.dp),

                        // on below line we are adding color for our text
                        color = Color.Black, textAlign = TextAlign.Center
                    )
                    // on below line inside row we are adding spacer
                    Spacer(modifier = Modifier.width(5.dp))

                    // on the below line we are creating a text.
                    Text(
                        // inside the text on below line we are
                        // setting text as the language name
                        // from our modal class.
                        text = "Course Tracks : " + courseList[index].courseTracks,

                        // on below line we are adding padding
                        // for our text from all sides.
                        modifier = Modifier.padding(4.dp),

                        // on below line we are adding color for our text
                        color = Color.Black, textAlign = TextAlign.Center
                    )
                    // on below line inside row we are adding spacer
                    Spacer(modifier = Modifier.width(5.dp))

                    // on the below line we are creating a text.
                    Text(
                        // inside the text on below line we are
                        // setting text as the language name
                        // from our modal class.
                        text = "Course Duration : " + courseList[index].courseDuration,

                        // on below line we are adding padding
                        // for our text from all sides.
                        modifier = Modifier.padding(4.dp),

                        // on below line we are adding color for our text
                        color = Color.Black, textAlign = TextAlign.Center
                    )
                    // on below line inside row we are adding spacer
                    Spacer(modifier = Modifier.width(5.dp))

                    // on the below line we are creating a text.
                    Text(
                        // inside the text on below line we are
                        // setting text as the language name
                        // from our modal class.
                        text = "Description : " + courseList[index].courseDescription,

                        // on below line we are adding padding
                        // for our text from all sides.
                        modifier = Modifier.padding(4.dp),

                        // on below line we are adding color for our text
                        color = Color.Black, textAlign = TextAlign.Center
                    )
                }
            }
        }
    }
}

Now run your application to see the output of it. 

Output: