Job retries and error handling in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the number of retries for a job.

Ruby on Rails

class MyJob < ApplicationJob
  retry_on StandardError, wait: 5.seconds, attempts: [1]
  def perform
    # job code here
  end
end

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

A5

B10

C0

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Setting attempts to 0 disables retries.

Using a string instead of a number for attempts.

The attempts option sets how many times the job will retry on failure. Here, 5 retries are set.

2fill in blank

medium

Complete the code to handle a specific error type with a custom retry wait time.

Ruby on Rails

class MyJob < ApplicationJob
  retry_on [1], wait: 10.seconds, attempts: 3
  def perform
    # job code here
  end
end

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

AStandardError

BActiveRecord::RecordNotFound

CNet::OpenTimeout

DArgumentError

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic error like StandardError when a specific error is needed.

Choosing an error unrelated to network issues.

The job retries on Net::OpenTimeout errors with a 10-second wait between attempts.

3fill in blank

hard

Fix the error in the retry_on syntax to correctly retry on exceptions.

Ruby on Rails

class MyJob < ApplicationJob
  retry_on StandardError, wait: [1], attempts: 4
  def perform
    # job code here
  end
end

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

A5.seconds

B5

C5s

Dseconds(5)

Attempts:

3 left

💡 Hint

Common Mistakes

Using a plain number instead of a duration.

Using invalid syntax like '5s' or 'seconds(5)'.

The wait option requires a duration object like 5.seconds, not a plain number.

4fill in blank

hard

Fill both blanks to correctly rescue an error and retry the job with a delay.

Ruby on Rails

class MyJob < ApplicationJob
  rescue_from [1] do |exception|
    retry_job wait: [2]
  end
  def perform
    # job code here
  end
end

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AActiveRecord::Deadlocked

BStandardError

C10.seconds

D5.minutes

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic error instead of the specific deadlock error.

Setting the wait time to a non-duration value.

The job rescues ActiveRecord::Deadlocked errors and retries after 10 seconds.

5fill in blank

hard

Fill all three blanks to create a job that retries on two errors with different wait times.

Ruby on Rails

class MyJob < ApplicationJob
  retry_on [1], wait: [2], attempts: 3
  retry_on [3], wait: 20.seconds, attempts: 2
  def perform
    # job code here
  end
end

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

ANet::OpenTimeout

B15.seconds

CActiveRecord::Deadlocked

DStandardError

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up error classes and wait times.

Using non-duration values for wait times.

The job retries on StandardError with a 15-second wait and on ActiveRecord::Deadlocked with a 20-second wait.

Practice

1. What does the retry_on method do in a Rails Active Job?

easy

A. It retries the job automatically if a specified error occurs.

B. It discards the job immediately without retrying.

C. It schedules the job to run only once without retries.

D. It logs the error but does not retry the job.

Solution

1. Step 1: Understand retry_on purpose

   The retry_on method tells Rails to retry a job if a certain error happens during execution.

2. Step 2: Compare with other options

   Unlike discard_on, which stops retries, retry_on allows automatic retrying.

3. Final Answer:

   It retries the job automatically if a specified error occurs. -> Option A

4. Quick Check:

   retry_on = automatic retry [OK]

Hint: Remember: retry_on means try again on error [OK]

Common Mistakes:

• Confusing retry_on with discard_on
• Thinking retry_on discards the job
• Assuming retry_on logs errors only

2. Which of the following is the correct syntax to retry a job on ActiveRecord::Deadlocked error with 3 attempts in Rails?

easy

A. retry_on(ActiveRecord::Deadlocked, attempts: 3)

B. retry_on ActiveRecord::Deadlocked attempts=3

C. retry_on ActiveRecord::Deadlocked attempts: 3

D. retry_on(ActiveRecord::Deadlocked attempts: 3)

Solution

1. Step 1: Recall method call syntax in Ruby

   Methods with arguments and options require parentheses for clarity, especially with keyword arguments.

2. Step 2: Check each option's syntax

   retry_on(ActiveRecord::Deadlocked, attempts: 3) uses parentheses and correct keyword argument syntax: retry_on(ActiveRecord::Deadlocked, attempts: 3).

3. Final Answer:

   retry_on(ActiveRecord::Deadlocked, attempts: 3) -> Option A

4. Quick Check:

   Correct method call syntax = retry_on(ActiveRecord::Deadlocked, attempts: 3) [OK]

Hint: Use parentheses with keyword args for retry_on [OK]

Common Mistakes:

• Omitting parentheses with keyword arguments
• Using equal sign instead of colon for options
• Missing commas between arguments

3. Given this job code:

class MyJob < ApplicationJob
  retry_on StandardError, attempts: 2

  def perform
    raise StandardError, "fail"
  end
end

MyJob.perform_now

What happens when MyJob.perform_now is called?

medium

A. The job silently discards the error and finishes.

B. The job raises StandardError once and stops.

C. The job retries twice after failures, then raises error.

D. The job retries once after the first failure, then raises error.

Solution

1. Step 1: Understand retry_on with attempts: 2

   It means the job will try up to 2 times total (1 initial + 1 retry) before giving up.

2. Step 2: Analyze job behavior

   The job raises StandardError every time. It runs once, fails, retries once, then fails again and raises error.

3. Final Answer:

   The job retries once after the first failure, then raises error. -> Option D

4. Quick Check:

   attempts: 2 means 1 retry [OK]

Hint: attempts count includes first try, so retries = attempts - 1 [OK]

Common Mistakes:

• Thinking attempts means retries count
• Assuming job discards error automatically
• Believing job retries infinitely

4. Identify the error in this job code snippet:

class ExampleJob < ApplicationJob
  retry_on(StandardError, attempts: 3)

  def perform
    # job logic
  end
end

medium

A. The retry_on method should be called inside perform method.

B. The retry_on method should not have parentheses.

C. The retry_on method is correctly used; no error.

D. The retry_on method should be declared with a block.

Solution

1. Step 1: Check retry_on usage location

   retry_on is a class-level method and should be declared outside perform method, as shown.

2. Step 2: Verify syntax correctness

   Using parentheses with arguments is valid Ruby syntax here.

3. Final Answer:

   The retry_on method is correctly used; no error. -> Option C

4. Quick Check:

   retry_on class method syntax is correct [OK]

Hint: retry_on is a class method, not inside perform [OK]

Common Mistakes:

• Placing retry_on inside perform method
• Thinking parentheses are disallowed
• Expecting retry_on to require a block

5. You want a job to retry up to 5 times on Net::OpenTimeout errors but discard immediately on ArgumentError. Which code correctly implements this behavior?

hard

A. class NetworkJob < ApplicationJob
discard_on Net::OpenTimeout
retry_on ArgumentError, attempts: 5

def perform
# network call
end
end

B. class NetworkJob < ApplicationJob
retry_on Net::OpenTimeout, attempts: 5
discard_on ArgumentError

def perform
# network call
end
end

C. class NetworkJob < ApplicationJob
retry_on Net::OpenTimeout
retry_on ArgumentError, attempts: 5

def perform
# network call
end
end

D. class NetworkJob < ApplicationJob
discard_on Net::OpenTimeout, attempts: 5
discard_on ArgumentError

def perform
# network call
end
end

Solution

1. Step 1: Understand retry_on and discard_on roles

   retry_on retries job on specified error; discard_on stops retries and discards job immediately.

2. Step 2: Match errors to correct methods

   Net::OpenTimeout should retry up to 5 times, so use retry_on with attempts: 5. ArgumentError should discard immediately, so use discard_on.

3. Final Answer:

   Code with retry_on Net::OpenTimeout, attempts: 5 and discard_on ArgumentError -> Option B

4. Quick Check:

   retry_on for retry, discard_on for discard [OK]

Hint: retry_on = retry; discard_on = stop and discard [OK]

Common Mistakes:

• Swapping retry_on and discard_on for errors
• Missing attempts option for retry_on
• Using discard_on with attempts option