SQLite with sqflite package in Flutter - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

What is the output of this Flutter widget using sqflite?

Consider this Flutter widget that fetches and displays a list of names from a SQLite database using sqflite. What will the UI show after the data is loaded?

Flutter

class NameList extends StatefulWidget {
  @override
  _NameListState createState() => _NameListState();
}

class _NameListState extends State<NameList> {
  List<String> names = [];

  @override
  void initState() {
    super.initState();
    loadNames();
  }

  Future<void> loadNames() async {
    final db = await openDatabase(':memory:');
    await db.execute('CREATE TABLE people (id INTEGER PRIMARY KEY, name TEXT)');
    await db.insert('people', {'name': 'Alice'});
    await db.insert('people', {'name': 'Bob'});
    final result = await db.query('people');
    setState(() {
      names = result.map((row) => row['name'] as String).toList();
    });
  }

  @override
  Widget build(BuildContext context) {
    return ListView(
      children: names.map((name) => Text(name)).toList(),
    );
  }
}

A A runtime error because the database is not opened correctly.

B An empty screen because the database is in memory and cleared immediately.

C A scrollable list showing two Text widgets: 'Alice' and 'Bob'.

D A single Text widget showing 'AliceBob' concatenated.

💡 Hint

Remember that ':memory:' creates a temporary database but it exists during the app runtime.

The code creates an in-memory database, inserts two names, queries them, and updates the UI. The ListView shows two Text widgets with 'Alice' and 'Bob'.

📝 Syntax

intermediate

What error does this sqflite query code produce?

Look at this sqflite query code snippet. What error will it raise?

Flutter

final db = await openDatabase('my.db');
final result = await db.query('users', where: 'id = ?', whereArgs: [5]);

A No error, query runs successfully.

B RuntimeError because the database file does not exist.

C SyntaxError due to wrong SQL syntax.

D TypeError because whereArgs expects a list but got an int.

💡 Hint

Check the type of whereArgs parameter.

The whereArgs parameter must be a list of arguments, but here it is given as a single int, causing a TypeError.

❓ lifecycle

advanced

When should you close the sqflite database in a Flutter app?

In a Flutter app using sqflite, when is the best time to close the database connection to avoid resource leaks?

A Only when the app is terminated or disposed of the database provider.

B Immediately after each query to free resources.

C Never close it; sqflite manages it automatically.

D After every screen navigation to a new page.

💡 Hint

Think about the app lifecycle and resource management.

Closing the database too early causes errors. The best practice is to close it when the app or the database provider is disposed to keep it open while needed.

🔧 Debug

advanced

Why does this sqflite insert not add data to the table?

This code runs without errors but the data is not saved. Why?

Flutter

final db = await openDatabase(':memory:');
await db.execute('CREATE TABLE IF NOT EXISTS items (id INTEGER PRIMARY KEY, name TEXT)');
await db.insert('items', {'name': 'Item1'});
final count = Sqflite.firstIntValue(await db.rawQuery('SELECT COUNT(*) FROM items'));
print(count);

A The insert is missing a transaction, so it is rolled back.

B The database is opened fresh each time, so previous data is lost.

C The database is opened but not awaited properly, so insert fails silently.

D The table creation SQL is incorrect, so insert does nothing.

💡 Hint

Check how the database file is opened and if it persists data.

If the database is opened fresh each time without a persistent path, data is lost between runs. Using a fixed path ensures data persists.

🧠 Conceptual

expert

Which option correctly describes sqflite transactions?

In sqflite, what is the main benefit of using transactions for multiple database operations?

A Transactions ensure all operations succeed or all fail, keeping data consistent.

B Transactions speed up queries by caching results automatically.

C Transactions allow running queries in parallel threads safely.

D Transactions automatically backup the database after each operation.

💡 Hint

Think about what happens if one operation in a group fails.

Transactions group operations so either all succeed or none do, preventing partial updates and keeping data consistent.

Practice

1. What is the primary purpose of the sqflite package in Flutter?

easy

A. To handle network requests and APIs

B. To manage SQLite databases for storing app data locally

C. To create user interfaces with widgets

D. To manage app navigation between screens

Solution

1. Step 1: Understand sqflite package role

   The sqflite package is designed to work with SQLite databases in Flutter apps.

2. Step 2: Identify main functionality

   It helps create, open, and manage local databases for storing app data persistently.

3. Final Answer:

   To manage SQLite databases for storing app data locally -> Option B

4. Quick Check:

   sqflite = SQLite database management [OK]

Hint: sqflite = SQLite database helper in Flutter [OK]

Common Mistakes:

• Confusing sqflite with UI or navigation packages
• Thinking sqflite handles network or API calls
• Assuming sqflite is for animations or gestures

2. Which of the following is the correct way to open a database using sqflite?

easy

A. db.open('my_db.db');

B. openDB('my_db.db');

C. await openDatabase('my_db.db');

D. Database.open('my_db.db');

Solution

1. Step 1: Recall sqflite openDatabase syntax

   The sqflite package provides an async function called openDatabase to open or create a database.

2. Step 2: Match correct syntax

   The correct usage is: await openDatabase('filename'); other options are not valid sqflite methods.

3. Final Answer:

   await openDatabase('my_db.db'); -> Option C

4. Quick Check:

   openDatabase is async and correct method [OK]

Hint: Use await openDatabase('filename') to open DB [OK]

Common Mistakes:

• Using non-existent methods like openDB or Database.open
• Forgetting to await the async openDatabase call
• Calling openDatabase without parentheses

3. Given this code snippet, what will be the output printed?

var db = await openDatabase('test.db');
await db.execute('CREATE TABLE IF NOT EXISTS users(id INTEGER PRIMARY KEY, name TEXT)');
await db.insert('users', {'id': 1, 'name': 'Alice'});
var result = await db.query('users');
print(result);

medium

A. SyntaxError

B. []

C. null

D. [{'id': 1, 'name': 'Alice'}]

Solution

1. Step 1: Analyze database operations

   The code opens a database, creates a table if missing, inserts one user, then queries all users.

2. Step 2: Understand query result

   The query returns a list of maps representing rows. Since one user was inserted, result contains one map with id and name.

3. Final Answer:

   [{'id': 1, 'name': 'Alice'}] -> Option D

4. Quick Check:

   Insert then query returns inserted row [OK]

Hint: Insert then query returns list with inserted rows [OK]

Common Mistakes:

• Expecting empty list if table was just created
• Confusing query result with null or error
• Not awaiting async calls causing runtime errors

4. What is wrong with this sqflite code snippet?

var db = await openDatabase('app.db');
await db.execute('CREATE TABLE users(id INTEGER PRIMARY KEY, name TEXT)');
await db.insert('users', {'id': 1, 'name': 'Bob'});
await db.insert('users', {'id': 1, 'name': 'Carol'});

medium

A. It tries to insert two rows with the same primary key, causing a conflict error

B. The table creation SQL syntax is incorrect

C. The insert method requires a third argument for conflictAlgorithm

D. openDatabase must be called with a version number

Solution

1. Step 1: Check table and inserts

   The table has id as PRIMARY KEY. Two inserts use the same id=1.

2. Step 2: Understand primary key constraint

   Inserting duplicate primary keys causes a conflict error unless handled explicitly.

3. Final Answer:

   It tries to insert two rows with the same primary key, causing a conflict error -> Option A

4. Quick Check:

   Duplicate primary keys cause insert conflict error [OK]

Hint: Primary key must be unique; duplicates cause errors [OK]

Common Mistakes:

• Assuming insert silently overwrites existing rows
• Thinking version is mandatory for openDatabase
• Believing insert always needs conflictAlgorithm argument

5. You want to update a user's name in the database using sqflite. Which code snippet correctly updates the user with id = 2 to have the name 'David'?

hard

A. await db.update('users', {'name': 'David'}, where: 'id = ?', whereArgs: [2]);

B. await db.insert('users', {'id': 2, 'name': 'David'});

C. await db.execute('UPDATE users SET name = 'David' WHERE id = 2');

D. await db.update('users', {'name': 'David'}, where: 'id = 2');

Solution

1. Step 1: Understand update method parameters

   The update method requires the table name, values map, and a where clause with arguments to avoid SQL injection.

2. Step 2: Check correct usage of where and whereArgs

   await db.update('users', {'name': 'David'}, where: 'id = ?', whereArgs: [2]); uses where: 'id = ?' and whereArgs: [2], which is the safe and correct way.

3. Final Answer:

   await db.update('users', {'name': 'David'}, where: 'id = ?', whereArgs: [2]); -> Option A

4. Quick Check:

   Use whereArgs with ? placeholders for safe updates [OK]

Hint: Use where with ? and whereArgs list for updates [OK]

Common Mistakes:

• Using raw SQL string without parameter binding
• Using insert instead of update to change data
• Omitting whereArgs causing errors or unsafe queries