Improve options to customize of ConversionService used for GraphQL argument binding

[MothF]

Spring Boot version: 2.7.0-M1
Spring GraphQL version: 1.0.0-M5

Hello. I faced a problem with arguments resolution when passing them to GraphQL controller methods

I have a declared method accepting some input DTO which may have field of one of the types: OffsetDateTime, ZonedDateTime, LocalDateTime. In terms of GraphQl variables it’s a date-formatted string.
There is also related graphql.schema.Coercing responsible for deserialization into java.time.Instant. So in general I want to convert java.time.Instant into correct date representation.

There are several cases where I need customization:

1. Controller plain argument mapping (ex. OffsetDateTime/ZonedDateTime it depends)
2. Controller DTO argument mapping (ex. TestInput)

In the first case I need a way to customize ConversionService but without overriding AnnotatedControllerConfigurer bean because it may have unpredictable consequences in future (as I'm developing custom library it would be impossible to maintain). For example it would be okay to call conversion service setter in some configuration PostConstruct method, but as for now it won’t have any effect because of hardcoded GraphQlArgumentInitializer at afterPropertySet method

In the second case there are several problems:

1. If I want to use no-args-constructor and setters deserialization GraphQlArgumentInitializer will use DataBinder. In such case if something is wrong with mapping into DTO DataBinder doesn’t throw any exception. In my opinion if DataBinder contains some errors they should be re-thrown as it’s done in all-args-constructor case.
2. There should be a way for DataBinder customization. As DataBinder is hardcoded I’m not able to do this. Check this line

So I think that ConversionService should be passed to DataBinder (something like this dataBinder.setConversionService(this.typeConverter.getConversionService());) and there should be an ability to customize ConversionService

If there is a workaround or my case is inapplicable I'd like to know about it. Also please check project with issues reproduction https://github.com/MothF/spring-graphql

Thank you in advance.

[rstoyanchev]

Indeed currently the ConversionService is created in the Boot starter without any option to customize. Not sure if we want to create a dedicated instance for GraphQL, or re-use the ones from Spring MVC and WebFlux. What do you think @bclozel?

On the side of AnnotatedControllerConfigurer we could defer the initialization by implementing SmartInitializingSingleton instead. That would allow more time to set the ConversionService.

As for setting the ConversionService on DataBinder that seems reasonable.

[rstoyanchev]

I've made the ConversionService a fixed, internally managed instance within AnnotatedControllerConfigurer that you can customize via FormatterRegistrar callbacks so you should be able to add one of those. It's also now passed on to the DataBindiner instance. Please, give this a try.

[MothF]

Thanks! I'll try it as soon as I can.
I have one more question about DataBinder, if you don't mind me asking. Is it suitable to throw an exception out of it? If I'm not mistaken DataBinder collects all problems during binding and stores them internally.
As an example Long overflow: in such case (when Long is DTO field) I'll receive null instead of exception. But with plain method argument everything is fine and exception is thrown

I've made the ConversionService a fixed, internally managed instance within AnnotatedControllerConfigurer that you can customize via FormatterRegistrar callbacks so you should be able to add one of those. It's also now passed on to the DataBindiner instance. Please, give this a try.

[rstoyanchev]

Good point about DataBinder errors. I've created #280 to address that.