Add support for defining a default DataFetcherFactory via autoconfig

[jord1e]

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Pull Request type

• Bugfix
• Feature
• Refactoring (no functional changes, no api changes)
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Changes in this PR

By default a PropertyDataFetcher will be configured when no data fetcher has been specified. You can provide a custom DataFetcherFactory to GraphQLCodeRegistry which gives you the ability to change this default behaviour.

I have been doing some work on dynamically generating the PropertyDataFetcher logic directly (instead of PropertyDataFetcher's reflection behaviour) in a class using the ASM bytecode library: https://github.com/jord1e/graphql-java-asm-datafetcher

By simply providing a AsmDataFetcherFactory the required classes get generated lazily, increasing performance by 10x+, matching handwritten data fetchers, in my initial testing (I will further work on this proof of concept to make it better match the default PropertyDataFetcher i.e. add generic Map<Object, Object> support).

This is not the only use-case of course but the ability to define a DataFetcherFactory as a bean is a low maintaince thing we can do.

Alternatives considered

N/A, Spring for GraphQL has a way to customize the GraphQL instance, I don't think DGS has this.

[berngp]

Interesting, thanks for the pr @jord1e