Job chaining and batching in Laravel - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is job chaining in Laravel?

Job chaining allows you to run multiple jobs in a specific order, where each job starts only after the previous one finishes successfully.

beginner

How do you create a job chain in Laravel?

You use the chain() method on the Bus facade, passing an array of jobs to run in sequence.

intermediate

What is job batching in Laravel?

Job batching lets you dispatch a group of jobs together and then track their progress or completion as a single batch.

intermediate

How can you detect when all jobs in a batch have finished?

Laravel provides batch callbacks like then() to run code after all jobs in the batch complete successfully.

beginner

What happens if a job in a chain fails?

If a job in a chain fails, the following jobs in the chain will not run, stopping the sequence.

Which method is used to start a job chain in Laravel?

A batch()

B chain()

C dispatchChain()

D queueChain()

The chain() method is used to create a sequence of jobs that run one after another.

What does Laravel's job batching allow you to do?

A Group jobs and track their overall progress

B Run jobs one by one without tracking

C Run jobs only on the main thread

D Automatically retry failed jobs forever

Job batching groups jobs and lets you monitor their progress or completion as a batch.

If a job in a chain fails, what happens next?

A The entire chain stops running

B The chain continues with the next job

C The failed job is skipped and retried later

D The batch is canceled

A failure in a job chain stops the chain from continuing to the next jobs.

Which callback runs after all jobs in a batch finish successfully?

A catch()

B finally()

C then()

D done()

The then() callback runs after all batch jobs complete successfully.

How do you dispatch a batch of jobs in Laravel?

A Batch::dispatch([...])

B Job::batch([...])->run()

C Queue::chain([...])->dispatch()

D Bus::batch([...])->dispatch()

You use Bus::batch([...])->dispatch() to dispatch a batch of jobs.

Explain how job chaining works in Laravel and why it might be useful.

Think about tasks that need to happen one after another.

Describe job batching in Laravel and how you can track when all jobs finish.

Imagine sending many jobs at once and waiting for all to complete.

Practice

1. What is the main difference between job chaining and job batching in Laravel?

easy

A. Job chaining is for database tasks only; job batching is for email tasks only.

B. Job chaining runs jobs in parallel; job batching runs jobs sequentially.

C. Job chaining runs jobs one after another; job batching runs jobs together and tracks progress.

D. Job chaining requires manual tracking; job batching does not track progress.

Solution

1. Step 1: Understand job chaining

   Job chaining runs jobs one after another in a specific order.

2. Step 2: Understand job batching

   Job batching runs many jobs together and tracks their progress as a group.

3. Final Answer:

   Job chaining runs jobs one after another; job batching runs jobs together and tracks progress. -> Option C

4. Quick Check:

   Job chaining = sequential, Job batching = grouped with progress [OK]

Hint: Chaining = sequence; batching = group with progress tracking [OK]

Common Mistakes:

• Confusing parallel and sequential execution
• Thinking batching runs jobs one by one
• Assuming chaining tracks progress automatically

2. Which of the following is the correct syntax to chain two jobs JobA and JobB in Laravel?

easy

A. JobA::chain([new JobB])->dispatch();

B. JobA::dispatch()->chain([JobB]);

C. dispatch(new JobA)->chain(new JobB);

D. dispatch(new JobA)->chain([new JobB]);

Solution

1. Step 1: Recall chaining syntax

   In Laravel, chaining jobs uses dispatch(new JobA)->chain([new JobB]).

2. Step 2: Check options for correct method calls

   dispatch(new JobA)->chain([new JobB]); matches the correct syntax with dispatch(new JobA)->chain([new JobB]);.

3. Final Answer:

   dispatch(new JobA)->chain([new JobB]); -> Option D

4. Quick Check:

   dispatch + chain array = correct chaining syntax [OK]

Hint: Use dispatch(new Job)->chain([jobs]) for chaining [OK]

Common Mistakes:

• Calling chain() on the job class instead of dispatch
• Passing a single job without array to chain()
• Using incorrect method order

3. Given the following code, what will be the output in the logs if all jobs succeed?

Bus::batch([
    new Job1(),
    new Job2(),
    new Job3()
])->then(function () {
    Log::info('Batch completed successfully');
})->dispatch();

medium

A. Logs 'Batch completed successfully' immediately after dispatch.

B. Logs 'Batch completed successfully' after all jobs finish.

C. No logs will be created because then() is not supported.

D. Logs 'Batch failed' if any job fails.

Solution

1. Step 1: Understand batch then() callback

   The then() callback runs after all jobs in the batch succeed.

2. Step 2: Analyze the code behavior

   Since all jobs succeed, the callback logs 'Batch completed successfully' after finishing.

3. Final Answer:

   Logs 'Batch completed successfully' after all jobs finish. -> Option B

4. Quick Check:

   Batch then() runs after success [OK]

Hint: then() runs after all batch jobs succeed [OK]

Common Mistakes:

• Thinking then() runs immediately after dispatch
• Assuming then() runs on failure
• Believing no logs are created

4. Identify the error in this job chaining code:

dispatch(new JobA)->chain(new JobB);

medium

A. chain() expects an array of jobs, not a single job instance.

B. dispatch() cannot be used with chaining.

C. JobB must be dispatched separately before chaining.

D. JobA must be a queued job class, not a job instance.

Solution

1. Step 1: Check chain() parameter requirements

   The chain() method requires an array of job instances.

2. Step 2: Analyze the code

   The code passes a single job instance new JobB without wrapping it in an array.

3. Final Answer:

   chain() expects an array of jobs, not a single job instance. -> Option A

4. Quick Check:

   chain() needs array of jobs [OK]

Hint: Always pass an array to chain(), even for one job [OK]

Common Mistakes:

• Passing a single job without array to chain()
• Trying to dispatch chained jobs separately
• Confusing dispatch and chain usage

5. You want to run three jobs JobX, JobY, and JobZ where JobY should only run after JobX completes, but JobZ can run anytime in parallel. Which Laravel approach correctly handles this?

hard

A. Use job chaining for JobX and JobY, and dispatch JobZ separately.

B. Use job batching for all three jobs together.

C. Chain JobX, JobY, and JobZ in one chain to run sequentially.

D. Dispatch all three jobs separately without chaining or batching.

Solution

1. Step 1: Understand job dependencies

   JobY depends on JobX finishing first, so they must run sequentially.

2. Step 2: Consider JobZ's independence

   JobZ can run anytime, so it should run separately in parallel.

3. Step 3: Choose correct Laravel approach

   Use chaining for JobX and JobY, and dispatch JobZ separately to run in parallel.

4. Final Answer:

   Use job chaining for JobX and JobY, and dispatch JobZ separately. -> Option A

5. Quick Check:

   Chain dependent jobs, dispatch independent jobs separately [OK]

Hint: Chain dependent jobs; dispatch independent jobs separately [OK]

Common Mistakes:

• Batching all jobs when order matters only for some
• Chaining all jobs forcing sequential run
• Ignoring job dependencies