cached_transformer.md

CachedTransformer

Wrap a chain of transformers with a PSR-6 cache layer. A cache key is built from the input value; if the cache contains an item for this key it is returned directly, otherwise the wrapped transformers are applied and the result is stored in cache.

Transformer reference

• Service: CleverAge\ProcessBundle\Transformer\CachedTransformer
• Transformer code: cached

Accepted inputs

any: the value is used both to build the cache key (after key_transformers) and as input of transformers. The key value must be a string once key_transformers are applied, otherwise the cache is bypassed (see Notes).

Possible outputs

any: result of the transformers chain, or the cached value on cache hit.

Options

Code	Type	Required	Default	Description
cache_key	string	X		Root of the cache key. The final key is <cache_key>|<rawurlencode(key value)>
ttl	string|DateTimeInterface|null		null	Expiration date of the cache items. A string is converted with new \DateTime($value) (e.g. +1 hour). null means no expiry
transformers	array		[]	Transformers applied on cache miss, see TransformerTrait
key_transformers	array		[]	Transformers applied on the input to compute the key value, see TransformerTrait

Examples

• Cache a costly transformation for one hour, using a slugified input as key

# Transformer options level
cached:
  cache_key: my_prefix
  ttl: '+1 hour'
  key_transformers:
    slugify: ~
  transformers:
    callback:
      callback: md5

Notes

• The cache pool is the cache.app service, passed explicitly. To use another pool, override the $cache argument of the CleverAge\ProcessBundle\Transformer\CachedTransformer service in your application (arguments: { $cache: '@cache.my_pool' }). Items are saved with saveDeferred(), a warning is logged if the save fails.
• A string ttl is converted to a date when the options are resolved (i.e. once, when the transformer is configured), not each time an item is saved: all items share the same absolute expiration date.
• If the key value is not a string after key_transformers (e.g. an int input without a cast key transformer), or if the cache pool raises a PSR-6 InvalidArgumentException (logged as a warning), the transformers are applied without cache.