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Whenever you need to store the data on the local then you need to use SQLite to persist the user data.

 

Why Data Persistence?

Persisting data is important for users since it would be inconvenient for them to type their information every time or wait for the network to load the same data again. In situations like this, it would be better to save their data locally.

Why we use SQLite?

SQLite is a popular choice as embedded database software for local/client storage in application software such as web browsers.

How to use SQLite in a flutter?

Before using SQLite, you should know that

SQLite is not available in a flutter SDK as Android but we have a plugin sqflite that exactly performs all the operation on the database just like in Android and iOS.

Flutter plugin is the wrapper of the native code written in Kotlin or java for Android and swift or objective-c for iOS. P.S : Plugin can also be created only with dart code

If you are new to SQLite, go through SQLite Tutorial site here.

Implementation

Step 1: Add the dependencies

To work with SQLite databases, import the sqflite and path packages

1. The sqflite package provides classes and functions that allow you to interact with a SQLite database. 2. The path_provider package provides functions that allow you to correctly define the location to store the database on disk such as TemporaryDirectory and ApplicationDocumentsDirectory.

Step 2: Create a Model class

SQLite creates a table for the model class, the fields in the class correspond to columns in the table. Therefore, the classes tend to be small model classes that don’t contain any logic. Our Person class represents the model for the data in the database.

If we want to insert into the database then we need to convert the Person into a Map

And if we want to retrieve from the database then we need to convert the Map into the Person

This is how our PODO class will look like

Step 3: Create a database

We will make a separate class as database.dart to make the code more modular and add all the requirements meths for managing the database that can be accessed anywhere in the app.

Create a singleton class DatabaseProvider

Why Singleton? We use the singleton pattern to ensure that we have only one class instance and provide global point access to it.

How to create a Singleton in Dart? Create a private constructor that can be used only inside the class.

Step 4: Open the Database

Before you read and write data to the database, you need to open a connection to the database. This involves two steps:

1. Define the path to the database file using the getDatabasesPath from the sqflite package combined with the pathfunction from the path package 2. Open the database with the openDatabase function from sqflite

Step 5: Create the table

You need to create a table to store information. For example, In our case, we create a table called Person that defines the data that can be stored. In this case, each Person contains an id, name, and city. Therefore, these will be represented as three columns in the Person table.

1. The id is a Dart int, and will be stored as an INTEGER SQLite Datatype. It is also good practice to use an id as the primary key for the table to improve query and update times. 2. The name is a Dart String, and will be stored as a TEXT SQLite Datatype 3. The city is also a Dart String, and will be stored as an TEXT Datatype

To prevent from opening a connection to the database again and again we can use this:

Step 6: Managing the data

Now we are going to show you how you can perform an operation on the SQLite database.

Query:

getAllPersons() will return all the person from the SQLite database if available.

Insert:

Delete:

If you see we have two methods, one deletes the row with particular id and other deletes all data present in the table, you can change all the query according to your need.

Update:

If these small code snippets still confuse you we have the complete code of the database class:

Step 7: Using the data

In order to use the database we need to create the instance of the database and use the method present in the database class

DatabaseProvider.db

This will help us to perform an operation on the database.

like if we want to get  the person in the database we will use the method that we have defined in our DatabaseProvider class

DatabaseProvider.db.getAllPersons()

And if I want to display it in the list then I’ll use FututeBuilder :

What is SharedPreferences

SharedPreferences is used for storing data key-value pair in the Android and iOS.

SharedPreferences in flutter uses NSUserDefaults on iOS and SharedPreferences on Android, providing a persistent store for simple data.

Why use SharedPreferences in Flutter?

Suppose you wanna save a small value (a flag probably) that you wanna refer later sometime when a user launches the application. Then shared preference comes into action.

We do not use SQLite for saving small values because then you will need to write lengthy codes and supporting classes.

Shared Preference let you read and write key-value pair in a couple of lines easily. But always remember, shared preference is not a solution for you to keep complex relational data.

How to use SharedPreferences in Flutter?

Before using SharedPreferences, you should know that Flutter SDK does not have support SharedPreferences but fortunately, the shared_preferences plugin can be used to persist key-value data on disk.

Implementation

Step 1: Add the dependencies

Add dependencies to pubspec.yaml file.

dependencies:
  flutter:
    sdk: flutter
  shared_preferences: "<newest version>"

Step 2: Import shared_preferences.dart

import 'package:shared_preferences/shared_preferences.dart';

Step 3: Save data

We can only add int, String, double and bool using SharedPreferences.

There are setter methods in the SharedPreferences class which take two parameters, key and value.

Note : keys are only string values

Saving String value

Saving int value

Saving double value

Saving boolean value

Step 4: Read data

When we are reading the data from the storage through SharedPreferences we only required to pass the key only.

If the value is not present in the storage then we might get a null value. To handle this we can use

int intValue = prefs.getInt('intValue') ?? 0;

Step 5: Remove data

To remove the data from the storage we provide the key in the remove(String key) method.

Check value if present or not?

SharedPreferences prefs = await SharedPreferences.getInstance();

bool CheckValue = prefs.containsKey('value');

containsKey will return true if persistent storage contains the given key and false if not.