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Date: Wed, 28 Oct 2020 17:57:11 +0000
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Subject: Re: [PHP-DEV] List of attributes
From: rowan.collins@gmail.com (Rowan Tommins)

On 28/10/2020 16:58, Nicolas Grekas wrote:
> about why we'd need nested attributes, here is a discussion about 
> nested validation constraints:
> https://github.com/symfony/symfony/issues/38503


Thanks, it's useful to see some real-world examples. As I suspected, 
nearly all of these explicitly take a *list* of nested attributes, not a 
single attribute.

 > While most of the constraints receive the nested constraints as 
simple array, |Collection| however requires a mapping (field to 
constraint) and is usually combined with other composite constraints, 
which gives us a second nesting level.


There is much discussion of Collection as an edge case, but although the 
nested attributes are indeed inside a mapping, the *value* of that 
mapping is again a list of attributes. Single items are allowed, but 
this seems to be a special case for convenience.

In the below example from 
https://symfony.com/doc/current/reference/constraints/Collection.html 
the @Assert\Email could equivalently be written as an array with one item:

     /**
      * @Assert\Collection(
      *     fields = {
      *         "personal_email" = @Assert\Email,
      *         "short_bio" = {
      *             @Assert\NotBlank,
      *             @Assert\Length(
      *                 max = 100,
      *                 maxMessage = "Your short bio is too long!"
      *             )
      *         }
      *     },
      *     allowMissingFields = true
      * )
      */


This reinforces my earlier suggestion 
(https://externals.io/message/111936#112109) that #[Foo] in a nested 
context can simply imply an array of one attribute, rendering the above as:

#[Assert\Collection(
     fields: [
          "personal_email" => #[Assert\Email],
          "short_bio" => #[
                 Assert\NotBlank,
                 Assert\Length(
                       max: 100,
                       maxMessage: "Your short bio is too long!"
                )
         ]
     ],
     allowMissingFields: true
]


Regards,

-- 
Rowan Tommins (né Collins)
[IMSoP]