Creating tables (db.create_all) in Flask - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Flask class.

Flask

from flask import [1]

Drag options to blanks, or click blank then click option'

AModel

BApp

CDatabase

DFlask

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'App' instead of 'Flask' will cause an import error.

Trying to import 'Database' or 'Model' from flask is incorrect.

The Flask class is imported from the flask package to create the app instance.

2fill in blank

medium

Complete the code to create a Flask app instance.

Flask

app = [1](__name__)

Drag options to blanks, or click blank then click option'

AFlask

BApp

Ccreate_app

DApplication

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Application' or 'App' will cause a NameError.

Using 'create_app' is a pattern but not the class constructor.

The Flask class is called with __name__ to create the app instance.

3fill in blank

hard

Fix the error in the code to initialize SQLAlchemy with the app.

Flask

db = SQLAlchemy()
db.[1](app)

Drag options to blanks, or click blank then click option'

Ainitialize

Bstart

Cinit_app

Dcreate

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'initialize' or 'start' causes AttributeError.

Using 'create' is not a method of SQLAlchemy instance.

The method to link the SQLAlchemy object to the Flask app is init_app.

4fill in blank

hard

Fill both blanks to define a simple model with an id primary key and a name column.

Flask

class User(db.Model):
    id = db.Column(db.[1], primary_key=True)
    name = db.Column(db.[2](50))

Drag options to blanks, or click blank then click option'

AInteger

BString

CText

DFloat

Attempts:

3 left

💡 Hint

Common Mistakes

Using Text for id causes errors.

Using Float for name is incorrect.

The id column uses Integer type and is primary key. The name column uses String with max length 50.

5fill in blank

hard

Fill all three blanks to create tables in the database after app context is pushed.

Flask

with app.[1]():
    db.[2]()
    print('[3] tables created!')

Drag options to blanks, or click blank then click option'

Aapp_context

Bcreate_all

CDatabase

DApp

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'App' instead of 'app_context' causes errors.

Calling 'create' instead of 'create_all' misses table creation.

Use app_context() to push context, then call create_all() to create tables, and print a confirmation message.

Practice

1. What does the db.create_all() function do in a Flask application?

easy

A. It updates existing tables to match model changes automatically.

B. It deletes all tables from the database.

C. It creates all tables defined by your models in the database if they don't exist.

D. It runs all database queries defined in your app.

Solution

1. Step 1: Understand the purpose of db.create_all()

   This function creates tables in the database based on your model definitions if those tables do not already exist.

2. Step 2: Recognize what it does not do

   It does not delete tables, update existing tables, or run queries; it only creates missing tables.

3. Final Answer:

   It creates all tables defined by your models in the database if they don't exist. -> Option C

4. Quick Check:

   db.create_all() creates missing tables [OK]

Hint: Remember: create_all only adds missing tables, no updates [OK]

Common Mistakes:

• Thinking it updates existing tables automatically
• Confusing it with deleting tables
• Assuming it runs queries or migrations

2. Which of the following is the correct way to use db.create_all() in a Flask app?

easy

A. Call db.create_all() inside the Flask app context.

B. Call db.create_all() after closing the app.

C. Call db.create_all() before defining your models.

D. Call db.create_all() outside the Flask app context.

Solution

1. Step 1: Understand Flask app context requirement

   Database operations like db.create_all() must run inside the Flask app context to access configuration and database connections properly.

2. Step 2: Identify correct usage

   Calling db.create_all() inside the app context ensures tables are created without errors.

3. Final Answer:

   Call db.create_all() inside the Flask app context. -> Option A

4. Quick Check:

   db.create_all() requires app context [OK]

Hint: Always run db.create_all() inside app context [OK]

Common Mistakes:

• Calling create_all outside app context causing errors
• Calling create_all before models are defined
• Calling create_all after app is closed

3. Given this Flask code snippet, what will happen when db.create_all() is called?

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///test.db'
db = SQLAlchemy(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.String(50))

with app.app_context():
    db.create_all()

medium

A. An error will occur because the app context is missing.

B. A new table named 'user' will be created in the database if it doesn't exist.

C. The existing 'user' table will be dropped and recreated.

D. Nothing happens because create_all does not create tables.

Solution

1. Step 1: Check app context usage

   The code calls db.create_all() inside app.app_context(), so the context is correct.

2. Step 2: Understand create_all behavior

   It creates missing tables based on models. Since 'User' model exists, a 'user' table will be created if not present.

3. Final Answer:

   A new table named 'user' will be created in the database if it doesn't exist. -> Option B

4. Quick Check:

   create_all creates missing tables inside app context [OK]

Hint: create_all adds missing tables, does not drop existing [OK]

Common Mistakes:

• Thinking create_all drops tables
• Forgetting app context causes errors
• Assuming create_all does nothing

4. You run db.create_all() but your new model's table is not created. What is the most likely cause?

medium

A. All of the above.

B. You defined the model after calling db.create_all().

C. The database URI is incorrect or missing.

D. You forgot to run db.create_all() inside the Flask app context.

Solution

1. Step 1: Check app context usage

   Running db.create_all() outside app context causes tables not to be created.

2. Step 2: Check model definition timing and database URI

   If models are defined after calling db.create_all(), their tables won't be created. Also, an incorrect or missing database URI prevents connection.

3. Final Answer:

   All of the above. -> Option A

4. Quick Check:

   App context, model timing, and URI all affect create_all success [OK]

Hint: Check app context, model order, and DB URI if tables missing [OK]

Common Mistakes:

• Ignoring app context errors
• Calling create_all before defining models
• Not setting database URI correctly

5. You want to add a new column to an existing table after calling db.create_all(). What will happen if you call db.create_all() again without migrations?

hard

A. An error will occur because the table schema changed.

B. The new column will be added automatically to the existing table.

C. The existing table will be dropped and recreated with the new column.

D. Nothing changes; db.create_all() does not modify existing tables.

Solution

1. Step 1: Understand create_all limitations

   db.create_all() only creates missing tables; it does not alter existing tables or add columns.

2. Step 2: Recognize need for migrations

   To change existing tables (like adding columns), you must use migration tools such as Flask-Migrate.

3. Final Answer:

   Nothing changes; db.create_all() does not modify existing tables. -> Option D

4. Quick Check:

   create_all creates tables but does not alter existing ones [OK]

Hint: Use migrations to change tables; create_all only adds missing tables [OK]

Common Mistakes:

• Expecting create_all to update tables
• Not using migration tools for schema changes
• Assuming create_all drops and recreates tables