How to use flutter to read and write data to sqflite database

Flutter is an object-oriented programming language primarily used for mobile development. We need to connect with a database to create a working mobile application and implement the essential CRUDCreate, read, update and delete operations.

Imports

The required dependencies are as follows:

dependencies:
    flutter:
        sdk: flutter
    sqflite:
    path:

The required imports to establish a connection with the SQLite database are as follows:

import 'dart:async'
import 'package:path/path.dart'
import 'package:sqflite/sqflite.dart'
import 'package:flutter/widgets.dart'

In the above code:

  • Line 1: The async import is required to use 'await' calls in the code.

  • Line 2: The path package defines the disk location that stores our database.

  • Line 3: The sqflite package provides functions and classes to communicate with the database. It is an SQLite plugin for flutter.

  • Line 4: The flutter/widgets.dart import provides the widget library to our application.

Code

The communication between database and data occurs in the form of objects. So, we need to define what we want to insert into the database.

Suppose we are developing a student management system. Let's start with how to implement CRUD operations of the Student class.

Class implementation

Firstly, we need to define the Student class:

class Student{
    final String email;
    final String name;
    final int age;
    final String rollNo;
//constructor
    Student({
        required this.email,
        required this.name,
        required this.age,
        required this.rollNo,
    });
}

  • The final keyword declares a variable at runtime, and a value is assigned to it only once.

  • The required keyword represents that a value is necessary for the following variable.

  • The this keyword represents the current class and its variables.

Database connection

To use the CRUD operations, we need to establish a connection to the database first:

WidgetsFlutterBinding.ensureInitialized();
final db = openDatabase(
    join(await getDatabasesPath(),'studentDB'),
);

  • Line 1: The WidgetsFlutterBinding.ensureInitialized() function declares an instance that interacts with the flutter engine.

  • Line 2: The openDatabase() function establish a link of the database into a variable, and the join() function sets the path of the database.

We open a channel to the database named studentDB.

Note: To learn about await functionality, click here.

CRUD operations

Following is the implementation of the CRUD operations in a flutter:

Create

After defining the database, create the Student table by the following code:

WidgetsFlutterBinding.ensureInitialized();
final db = openDatabase(
    join(await getDatabasesPath(),'studentDB'),
    onCreate:(db,ver){
        return db.execute('CREATE TABLE Student(email TEXT PRIMARY KEY, name TEXT, age INTEGER, rollNo TEXT)',);
    },
    //version is used to execute onCreate and make database upgrades and downgrades.
    version:1,
);

  • Lines 4 to 6: The onCreate determines what the database should do once a link is established. Here, the db.execute() function is executed that contains the SQL query we need to use.

Insertion

Use the following code to insert a student object into the database:

class Student{
    final String email;
    final String name;
    final int age;
    final String rollNo;
//constructor
    Student({
        required this.email,
        required this.name,
        required this.age,
        required this.rollNo,
    });
    Map<String, dynamic> mapStudent() {
      return {
        'email': email,
        'name': name,
        'age': age,
        'rollNo':rollNo,
      };
   }
}

Note: mapStudent() function is required to convert a student object into a map object that can be stored in the database.

//the 'future' keyword defines a function that works asynchronously
Future<void> insertStudent(Student student) async{
  //local database variable
  final curDB = await db
  //insert function
  await curDB.insert(
    //first parameter is Table name
    'Student',
    //second parameter is data to be inserted
    student.mapStudent(),
    //replace if two same entries are inserted
    conflictAlgorithm: ConflictAlgorithm.replace,
  );
}

we are using insert() function to insert data in to student table.This will get two parameters

  • Table name

  • Data to be inserted

var studentOne = Student(email:'studentOne@gmail.com',name:'XYZ', age:20, rollNo:'2P-23');
await insertStudent(studentOne);
Read

Use the following code to retrieve students from the database:

Future<List<Student>> getStudents() async {
  final curDB = await db;
  //query to get all students into a Map list
  final List<Map<String, dynamic>> studentMaps = await curDB.query('Student');
  //converting the map list to student list
  return List.generate(studentMaps.length, (i) {
    //loop to traverse the list and return student object
    return Student(
      email: studentMaps[i]['email'],
      name: studentMaps[i]['name'],
      age: studentMaps[i]['age'],
      rollNo: studentMaps[i]['rollNo'],
    );
  });
}

To read data from table we are using generate function this will return the student object.

print(await getStudents());

Update

Use the following code to update the data of a specific student:

Future<void> updateStudent(Student student) async {
  final curDB = await db;
  //update a specific student
  await curDB.update(
    //table name
    'Student',
    //convert student object to a map
    student.mapStudent(),
    //ensure that the student has a matching email
    where: 'email = ?',
    //argument of where statement(the email we want to search in our case)
    whereArgs: [student.email],
  );
}
var studentUpdate = Student(
  email: studentOne.email,
  name: studentOne.name,
  age: studentOne.age + 7,
  rollNo: studentOne.rollNo,
);
await updateStudent(studentUpdate);
// Print the updated results.
print(await getStudents());
Delete

Use the following code for deletion:

Future<void> deleteStudent(String email) async {
  final curDB = await db;
  // Delete operation
  await curDB.delete(
    //table name
    'Student',
    //'where statement to identify a specific student'
    where: 'email = ?',
    //arguments to the where statement(email passed as parameter in our case)
    whereArgs: [email],
  );
}

To delete some recoed we can use delete() function which will get two parameters first is table name and second one is any query parameter which is used to select a record.

deleteStudent("studentOne@gmail.com")

Combined code

The main.dart file should look like the following code:

import 'dart:async';
import 'package:path/path.dart';
import 'package:sqflite/sqflite.dart';
import 'package:flutter/widgets.dart';
//db variable
var db;
//main function
void main() async{
  WidgetsFlutterBinding.ensureInitialized();
  //connection and creation
   db = openDatabase(
      join(await getDatabasesPath(),'studentDB'),
      onCreate:(db,ver){
      return db.execute('CREATE TABLE Student(email TEXT PRIMARY KEY, name TEXT, age INTEGER, rollNo TEXT)',);        
      },
    //version is used to execute onCreate and make database upgrades and downgrades.
      version:1,    
    );
  //insertion
  var studentOne = Student(email:'studentOne@gmail.com',name:'XYZ', age:20, rollNo:'2P-23');
  await insertStudent(studentOne);
  //read
  print(await getStudents());
  //updation
  var studentUpdate = Student(
    email: studentOne.email,
    name: studentOne.name,
    age: studentOne.age + 7,
    rollNo: studentOne.rollNo,
  );
  await updateStudent(studentUpdate);
  // Print the updated results.
  print(await getStudents());
  //deletion
  deleteStudent("studentOne@gmail.com");
}
//Class
class Student{
    final String email;
    final String name;
    final int age;
    final String rollNo;
//constructor
    Student({
        required this.email,
        required this.name,
        required this.age,
        required this.rollNo,
    });
    Map<String, dynamic> mapStudent() {
      return {
        'email': email,
        'name': name,
        'age': age,
        'rollNo':rollNo,
      };
    }
}
//Insert
  //the 'future' keyword defines a function that works asynchronously
Future<void> insertStudent(Student student) async{
  //local database variable
  final curDB = await db;
  //insert function
  await curDB.insert(
    //first parameter is Table name
    'Student',
    //second parameter is data to be inserted
    student.mapStudent(),
    //replace if two same entries are inserted
    conflictAlgorithm: ConflictAlgorithm.replace,
  );
}
//Read
Future<List<Student>> getStudents() async {
  final curDB = await db;
  //query to get all students into a Map list
  final List<Map<String, dynamic>> studentMaps = await curDB.query('Student');
  //converting the map list to student list
  return List.generate(studentMaps.length, (i) {
    //loop to traverse the list and return student object
    return Student(
      email: studentMaps[i]['email'],
      name: studentMaps[i]['name'],
      age: studentMaps[i]['age'],
      rollNo: studentMaps[i]['rollNo'],
    );
  });
}
//Update
Future<void> updateStudent(Student student) async {
  final curDB = await db;
  //update a specific student
  await curDB.update(
    //table name
    'Student',
    //convert student object to a map
    student.mapStudent(),
    //ensure that the student has a matching email
    where: 'email = ?',
    //argument of where statement(the email we want to search in our case)
    whereArgs: [student.email],
  );
}
//Delete
Future<void> deleteStudent(String email) async {
  final curDB = await db;
  // Delete operation
  await curDB.delete(
    //table name
    'Student',
    //'where statement to identify a specific student'
    where: 'email = ?',
    //arguments to the where statement(email passed as parameter in our case)
    whereArgs: [email],
  );
}

Explanation

  • Line 11 – 18: We create and connect to a database named studentDB and create a table named Student.

  • Line 21 – 22: We insert a student in our table named Student using the insert keyword.

  • Line 24: We read a table named student using the getStudents() function.

  • Line 26 – 32 : We update the existing record of the student using the updateStudent() function.

  • Line 36 : We delete the record containing the given email using the deleteStudent() function.

  • Line 39 – 59 : We create a model of student class named Student .

  • Line 62 – 72 : We create a function for the insertion of student data named as insertStudent using the insert() function in which first parameter is table_name and the second parameter is the data to be inserted.

  • Line 76 – 90 : We create a function for reading student data from the table named as getStudents .

  • Line 95 – 105 : We create a function for updating student data in the Student table named as updateStudent .

  • Line 107 – 118 : We create a function named as deleteStudent to delete a record from student table. here we are using Where clause to identify a specific student to which we want to delete.

Note : Here we are using future key word while creating the function this will create an asynchronous function.

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