Where conditions in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to find all users with the name 'Alice'.

Ruby on Rails

User.where(name: [1])

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

A'name'

B:Alice

CAlice

D"Alice"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a symbol instead of a string for the value.

Forgetting quotes around the string.

In Rails, to query by a string value, you need to pass the string in quotes. Here, "Alice" is correct.

2fill in blank

medium

Complete the code to find all orders with status 'completed'.

Ruby on Rails

Order.where(status: [1])

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

A"completed"

B'status'

Ccompleted

D:completed

Attempts:

3 left

💡 Hint

Common Mistakes

Using a symbol instead of a string for the status value.

Not quoting the string value.

The status value is a string, so it must be quoted. "completed" is correct.

3fill in blank

hard

Fix the error in the code to find products with price greater than 100.

Ruby on Rails

Product.where("price [1] ?", 100)

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

A=

B<

C>

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' which checks for equality, not greater than.

Using '<' which checks for less than.

The condition should check for prices greater than 100, so the operator '>' is correct.

4fill in blank

hard

Fill both blanks to find users created after 2020-01-01 and with active status true.

Ruby on Rails

User.where("created_at [1] ? AND active = [2]", Date.new(2020,1,1), true)

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

A>

B<

Ctrue

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' for date comparison.

Using 'false' instead of 'true' for active status.

The query finds users created after a date, so '>' is correct. Active status true means 'true'.

5fill in blank

hard

Fill all three blanks to find posts with title containing 'Rails', published before 2023-01-01, and views greater than 1000.

Ruby on Rails

Post.where("title LIKE ? AND published_at [1] ? AND views [2] ?", [3], Date.new(2023,1,1), 1000)

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

A<

B>

C"%Rails%"

D"Rails"

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' instead of LIKE for text matching.

Using '>' instead of '<' for published_at date.

Using '<' instead of '>' for views.

Title uses LIKE with '%Rails%' to find containing text. Published before date uses '<'. Views greater than 1000 uses '>'.

Practice

1. What does the where method do in Rails ActiveRecord?

easy

A. Creates a new database table

B. Deletes records from the database

C. Updates all records without conditions

D. Filters records based on given conditions

Solution

1. Step 1: Understand the purpose of where

   The where method is used to specify conditions to filter records in a database query.

2. Step 2: Compare with other database actions

   Deleting, creating tables, or updating all records are different methods like delete, migrations, or update_all.

3. Final Answer:

   Filters records based on given conditions -> Option D

4. Quick Check:

   where filters records = C [OK]

Hint: Remember: where narrows down records by conditions [OK]

Common Mistakes:

• Confusing where with delete or update methods
• Thinking where creates or deletes tables
• Assuming where modifies all records without conditions

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

easy

A. User.where('age == ?', 30)

B. User.where(age: 30)

C. User.where(age == 30)

D. User.where(age = 30)

Solution

1. Step 1: Identify correct hash syntax for where

   Using a hash like age: 30 is the standard way to filter by attribute value.

2. Step 2: Check other options for syntax errors

   User.where('age == ?', 30) uses invalid SQL operator ==; User.where(age == 30) uses invalid Ruby comparison inside where; User.where(age = 30) uses assignment instead of comparison.

3. Final Answer:

   User.where(age: 30) -> Option B

4. Quick Check:

   Hash syntax for where = A [OK]

Hint: Use hash syntax for simple where conditions [OK]

Common Mistakes:

• Using == inside where instead of hash or string
• Using = instead of : or ? for conditions
• Confusing string and hash syntax

3. What will this code return?

User.where("name LIKE ?", "%John%")

medium

A. All users with name containing 'John'

B. All users with name exactly 'John'

C. Syntax error due to quotes

D. No users because LIKE is invalid

Solution

1. Step 1: Understand the SQL LIKE operator

   LIKE with % means match any characters before or after 'John', so it finds names containing 'John'.

2. Step 2: Check the where syntax

   The string with placeholder and argument is correct syntax for complex conditions.

3. Final Answer:

   All users with name containing 'John' -> Option A

4. Quick Check:

   LIKE with % means contains = A [OK]

Hint: LIKE with % means contains substring [OK]

Common Mistakes:

• Thinking LIKE matches exact string only
• Confusing syntax with invalid quotes
• Assuming LIKE is not supported in where

4. Identify the error in this code:

User.where(age > 25)

medium

A. Incorrect use of > inside where without string

B. Should use User.find instead of where

C. No error, code works fine

D. Missing quotes around condition string

Solution

1. Step 1: Check syntax of where conditions

   Conditions with operators like > must be inside a string or hash syntax; direct Ruby expressions are invalid.

2. Step 2: Identify correct usage

   Correct usage is User.where("age > ?", 25) or User.where("age > 25").

3. Final Answer:

   Incorrect use of > inside where without string -> Option A

4. Quick Check:

   Operators need string syntax in where = D [OK]

Hint: Use strings for operators like > in where [OK]

Common Mistakes:

• Writing Ruby expressions directly inside where
• Forgetting to quote conditions with operators
• Using find instead of where for filtering

5. How can you chain multiple where conditions to find users who are active and older than 18?

hard

A. User.where(active: true, age > ?, 18)

B. User.where('active = true AND age > ?')

C. User.where(active: true).where('age > ?', 18)

D. User.where(active == true).where(age > 18)

Solution

1. Step 1: Understand chaining of where

   Multiple where calls can be chained to combine conditions, each filtering further.

2. Step 2: Check syntax of each where call

   First where uses hash for simple boolean, second uses string with placeholder for age condition.

3. Step 3: Evaluate other options

   User.where(active: true, age > ?, 18) uses invalid Ruby expression without quotes; User.where('active = true AND age > ?') uses placeholder without bind argument; User.where(active == true).where(age > 18) uses invalid Ruby expressions.

4. Final Answer:

   User.where(active: true).where('age > ?', 18) -> Option C

5. Quick Check:

   Chain where with hash and string = B [OK]

Hint: Chain where calls for multiple conditions [OK]

Common Mistakes:

• Mixing hash and string in one where call incorrectly
• Using == inside where instead of : or placeholders
• Not chaining where calls properly