Custom type in array key is not respected when serializing to JSON

[eduardoweiland]

Q	A
Bug report?	yes
Feature request?	no
BC Break report?	no
RFC?	no

I have a property annotated with key-value syntax for array, like @Type("array<K, V>"), where K is a custom type I defined. When a JSON is deserialized, the key is passed to my custom handler and it gets deserialized, as expected. But when it is serialized back to JSON, the custom handler is not called and the key is used as-is in the JSON output.

The custom type was defined to handle a map where the key was a database ID. In the API I'm working, all database IDs should be converted using Hashids. This handler is working well in other places, it just does not work for array keys. Also, I'm not sure how this might affect other formats, such as XML, as I'm only using JSON.

Steps required to reproduce the problem

I have created a small repo reproducing this problem: https://github.com/eduardoweiland/jmsserializer-json-map-key-transform

Expected Result

• Custom handler should be called to serialize array key

Actual Result

• Custom handler is not called to serialize array key

[eduardoweiland]

I managed to work around this problem by creating a new custom type to handle serialization of this kind of array.

[goetas]

type handlers on the array keys is something that is not supported (as min most of the cases keys are simple scalars as integers or strings).
I had a similar usecase in the past but decided to postpone it as it was impacting on performance and code complexity, for a very low number of cases where the feature is actually needed.

[eduardoweiland]

So the docs is misleading about this. It states array<K, V>: A map of keys of type K to values of type V. Examples: array<string, string>, array<string, MyNamespaceMyObject>, etc.

Based on this, I thought that any type K would work. But, in fact, type K is only used for deserializing and it's completely ignored when serializing. Maybe adding a note in the docs could clarify this limitation.

[goetas]

It would be great if you could add a note in the documentation about this (https://github.com/schmittjoh/serializer/tree/master/doc/reference)

[goetas]

solved in #1235