Miscellaneous

Question 1

Which PSR does Cache-Component follow?

Answer 1

PSR-6 & PSR-16

Question 2

Which interfaces/classes does the PSR-6 Cache-Component include?

Answer 2

• CacheException
• CacheItemInterface
• CacheItemPoolInterface
• InvalidArgumentException

Question 3

How will a value be set for a cache-item?

Answer 3

Within the method “get”

Question 4

How will a value be selected for a cache-item?

Answer 4

Within the method “get”

Question 5

What is stampede protection?

Answer 5

Protecting cold cache from being written by multiple clients at a time

Question 6

What are the 2 ways of symfony’s stampede protection?

Answer 6

1. lock
2. refresh before expiring

Question 7

Whats the difference between PSR-6 and PSR-16?

Answer 7

PSR-16 is the simplified and more performant way of caching, while PSR-6 allows more complex possibilities for caching (e.g. getItem, getDeferred etc.)

Question 8

Which Interfaces / Classes do the cache-contracts (PSR-16) include?

Answer 8

• CacheInterface
• ItemInterface

Question 9

What are ways to react on events?

Answer 9

EventSubscriber
EventListener

Question 10

Which interfaces / classes are part of the event-dispatcher component?

Answer 10

• EventDispatcherInterface (to dispatch the event)
• EventSubscriberInterface
• Event

Question 11

Which PSR defines the event-dispatcher component?

Answer 11

PSR-14
https://www.php-fig.org/psr/psr-14/

Question 12

Which method is implemented in the EventSubscriberInterface?

Answer 12

::getSubscribedEvents()

Question 13

What are ways to make an EventListener to listen to an Event?

Answer 13

EventListener
Registering with ->addEventListener

Question 14

How to add priority to an Event-listener / -subscriber?

Answer 14

with the parameter $priority

Question 15

How can you make sure the DI-Container is configured in a valid way?

Answer 15

php bin/console lint:container

Question 16

What are 2 ways to access services lazily from the DI-Container instead of using autowiring?

Answer 16

• service locator
• public service (not best practice)

Question 17

How and where can global parameters be configured?

Answer 17

In the services.yaml / services.php in the section “parameters:”

parameters:
    app.admin_email:'something@example.com'

Question 18

How can globally configured parameters be used in other configuration files?

Answer 18

config/packages/some_package.yaml

some_package:
    # any string surrounded by two % is replaced by that parameter value
    email_address: '%app.admin_email%'

Question 19

Where are additional packages being configured?

Answer 19

your-project/
├─ config/
│  ├─ packages/

Question 20

Where can the service container be configured?

Answer 20

your-project/
├─ config/
│  └─ services.yaml

Question 21

Where can routes be configured?

Answer 21

your-project/
├─ config/
│  ├─ routes.yaml

Question 22

Which configuration formats does symfony support?

Answer 22

PHP
XML
YAML

Question 23

How is the current environment defined in symfony?

Answer 23

Via the “APP_ENV” variable in the current .env

Question 24

How can you store and show custom data inside the toolbar?

Answer 24

Create an own datacollector by using the DataCollectorInterface

Question 25

How does tag-based cache invalidation work?

Answer 25

When getting a cache-item, tags can be added in its responsible callback. E.g: ``` $item = $cache->get('cache_key', function (ItemInterface $item): string { // add one or more tags $item->tag('tag_1'); $item->tag(['tag_2', 'tag_3']); return $cachedValue; }); ``` The cache can then be invalidated via the tag: ```$cache->invalidateTags(['tag_1', 'tag_3']);``` Alternatively, of course you can still delete the item via its cache-key: ```$cache->delete('cache_key');``` To be able to store tags, you need to use a TagAwareAdapter, for example like this: ``` use Symfony\Component\Cache\Adapter\FilesystemAdapter; use Symfony\Component\Cache\Adapter\RedisAdapter; use Symfony\Component\Cache\Adapter\TagAwareAdapter; $cache = new TagAwareAdapter( // Adapter for cached items new FilesystemAdapter(), // Adapter for tags new RedisAdapter('redis://localhost') ); ``` In this example, the tags are saved in redis, but the actual cache items in the FileSystem.

Question 26

Which cache invalidation methods are possible?

Answer 26

- tag-based invalidation - by expiration

Question 27

How can you lint an expression of the expression language?

Answer 27

``` $expressionLanguage = new ExpressionLanguage(); // does not throw a SyntaxError because the unknown variables and functions are ignored $expressionLanguage->lint('1 + 2', [])```

Question 28

How can you ignore errors when linting an expression of the expression language?

Answer 28

``` $expressionLanguage = new ExpressionLanguage(); // does not throw a SyntaxError because the unknown variables and functions are ignored $expressionLanguage->lint('unknown_var + unknown_function()', [], Parser::IGNORE_UNKNOWN_VARIABLES | Parser::IGNORE_UNKNOWN_FUNCTIONS); ```

Question 29

How can you provide a configured cache to the expression language?

Answer 29

``` $cache = new RedisAdapter(...); $expressionLanguage = new ExpressionLanguage($cache); ```

Question 30

How do you escape a backslash in expression language in a string?

Answer 30

With 3 leading backslashes

Question 31

How do you escape a backslash in expression language in a regex?

Answer 31

With 7 leading backslashes

Question 32

Whats the difference between the method mustRun() and run() in the process component?

Answer 32

mustRun() throws an exception if an error happens

Question 33

How can you start running a process asynchronously?

Answer 33

```$process->start()```

Question 34

How can you check if a process is still running?

Answer 34

```$process->isRunning()```

Question 35

How can you stop at a specific line of code until the process is finished?

Answer 35

```$process->wait()```

Question 36

How can you wait for a process to fulfill a specific condition?

Answer 36

``` $process->waitUntil(function ($type, $output): bool { return $output === 'Ready. Waiting for commands...'; }); ```

Question 37

How can you stop a running process?

Answer 37

``` $process->stop() ```

Question 38

Whats the default timeout of a process?

Answer 38

60 seconds

Question 39

How can you set the following: 1. the overall timeout for a process 2. the timeout for a process for being idle (not outputting anything)

Answer 39

``` $process->setTimeout(3600); $process->setIdleTimeout(60); $process->run(); ```

Question 40

How can you serialize objects inside twig?

Answer 40

```{{ person|serialize(format = 'json') }}```