Querying with filter and filter_by in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to query all users with the name 'Alice' using filter_by.

Flask

users = User.query.[1](name='Alice').all()

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

Aget

Bfilter

Call

Dfilter_by

Attempts:

3 left

💡 Hint

Common Mistakes

Using filter instead of filter_by with keyword arguments.

Using get which fetches by primary key.

The filter_by method allows filtering by keyword arguments like name='Alice'.

2fill in blank

medium

Complete the code to query users whose age is greater than 30 using filter.

Flask

users = User.query.[1](User.age > 30).all()

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

Afilter

Bfilter_by

Cget

Dorder_by

Attempts:

3 left

💡 Hint

Common Mistakes

Using filter_by with expressions causes errors.

Using order_by instead of filter for filtering.

The filter method accepts expressions like User.age > 30 for filtering.

3fill in blank

hard

Fix the error in the code to query users with email ending with '@example.com'.

Flask

users = User.query.[1](User.email.like('[e-mail]')).all()

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

Afilter

Bfilter_by

Cget

Dorder_by

Attempts:

3 left

💡 Hint

Common Mistakes

Using filter_by with expressions causes runtime errors.

Using get which fetches by primary key only.

Use filter with the like expression to filter by pattern.

4fill in blank

hard

Fill both blanks to query users with age less than 25 and name 'Bob'.

Flask

users = User.query.[1](User.age [2] 25, User.name == 'Bob').all()

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

Afilter

Bfilter_by

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using filter_by with expressions causes errors.

Using greater than operator instead of less than.

Use filter with multiple expressions: User.age < 25 and User.name == 'Bob'. The operator for less than is <.

5fill in blank

hard

Fill all three blanks to query users with name starting with 'A', age greater than 20, and order by age descending.

Flask

users = User.query.[1](User.name.like('A%'), User.age [2] 20).[3](User.age.desc()).all()

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

Afilter

B>

Corder_by

Dfilter_by

Attempts:

3 left

💡 Hint

Common Mistakes

Using filter_by instead of filter for expressions.

Using less than operator instead of greater than.

Not using order_by for sorting.

Use filter for expressions, the greater than operator >, and order_by to sort results.

Practice

1. What is the main difference between filter and filter_by in Flask querying?

easy

A. filter is used only for deleting records; filter_by is for selecting.

B. filter_by allows complex expressions; filter uses simple keyword arguments.

C. filter allows complex expressions; filter_by uses simple keyword arguments.

D. filter and filter_by are exactly the same in usage.

Solution

1. Step 1: Understand filter usage

   filter accepts expressions like User.age > 20, allowing detailed conditions.

2. Step 2: Understand filter_by usage

   filter_by uses simple keyword arguments like filter_by(name='John') for equality checks.

3. Final Answer:

   filter allows complex expressions; filter_by uses simple keyword arguments. -> Option C

4. Quick Check:

   filter = complex, filter_by = simple keyword [OK]

Hint: Remember: filter = expressions, filter_by = simple equals [OK]

Common Mistakes:

• Thinking filter_by supports complex expressions
• Confusing filter_by with filter in syntax
• Assuming both methods behave identically

2. Which of the following is the correct syntax to filter users with age 30 using filter_by?

easy

A. User.query.filter_by('age == 30').all()

B. User.query.filter_by(age=30).all()

C. User.query.filter_by(age == 30).all()

D. User.query.filter_by(age > 30).all()

Solution

1. Step 1: Check filter_by syntax

   filter_by accepts keyword arguments like age=30, not expressions or strings.

2. Step 2: Identify correct usage

   Only User.query.filter_by(age=30).all() uses correct keyword argument syntax.

3. Final Answer:

   User.query.filter_by(age=30).all() -> Option B

4. Quick Check:

   filter_by uses keyword arguments [OK]

Hint: Use keyword arguments without quotes or operators in filter_by [OK]

Common Mistakes:

• Passing expressions or strings to filter_by
• Using comparison operators inside filter_by
• Confusing filter_by with filter syntax

3. Given the model User with fields name and age, what will this query return?

users = User.query.filter(User.age > 25).filter_by(name='Alice').all()

medium

A. All users named Alice older than 25

B. All users older than 25, ignoring name

C. All users named Alice, ignoring age

D. Syntax error due to mixing filter and filter_by

Solution

1. Step 1: Understand chaining filters

   Chaining filter and filter_by combines conditions with AND logic.

2. Step 2: Analyze conditions

   filter(User.age > 25) filters age > 25, filter_by(name='Alice') filters name = 'Alice'. Both apply together.

3. Final Answer:

   All users named Alice older than 25 -> Option A

4. Quick Check:

   Chained filters combine conditions [OK]

Hint: Chained filters combine all conditions with AND [OK]

Common Mistakes:

• Thinking filter_by overrides filter
• Assuming only one filter applies
• Believing mixing filter and filter_by causes error

4. What is wrong with this query?

users = User.query.filter_by(User.age > 20).all()

medium

A. filter_by requires a list, not a condition

B. User.age > 20 is a valid filter_by argument

C. The query is correct and returns users older than 20

D. filter_by does not accept expressions, only keyword arguments

Solution

1. Step 1: Check filter_by argument type

   filter_by only accepts keyword arguments like age=20, not expressions.

2. Step 2: Identify error in usage

   Passing User.age > 20 is an expression, invalid for filter_by.

3. Final Answer:

   filter_by does not accept expressions, only keyword arguments -> Option D

4. Quick Check:

   filter_by = keyword args only [OK]

Hint: filter_by needs simple key=value pairs, not expressions [OK]

Common Mistakes:

• Passing expressions to filter_by
• Confusing filter_by with filter syntax
• Expecting filter_by to parse conditions

5. You want to find all users whose name starts with 'J' and are younger than 40. Which query correctly uses filter and filter_by together?

hard

A. User.query.filter(User.name.like('J%')).filter(User.age < 40).all()

B. User.query.filter_by(name='J%').filter_by(age < 40).all()

C. User.query.filter(User.name.like('J%')).filter_by(age=40).all()

D. User.query.filter_by(name.like('J%')).filter(User.age < 40).all()

Solution

1. Step 1: Use filter for complex conditions

   Checking if name starts with 'J' requires like('J%'), which is an expression needing filter.

2. Step 2: Use filter for age less than 40

   Age < 40 is also an expression, so filter is needed again. filter_by cannot handle expressions.

3. Step 3: Verify option correctness

   User.query.filter(User.name.like('J%')).filter(User.age < 40).all() uses filter twice with correct expressions. Others misuse filter_by or syntax.

4. Final Answer:

   User.query.filter(User.name.like('J%')).filter(User.age < 40).all() -> Option A

5. Quick Check:

   Use filter for expressions, filter_by for simple equals [OK]

Hint: Use filter for expressions like like() and comparisons [OK]

Common Mistakes:

• Using filter_by with expressions like like() or <
• Mixing filter_by with invalid syntax
• Assuming filter_by can handle partial matches