feat(core): support transforming config before model creation

[ronnetzer]

This feature adds the ability to add an array of model JSON transform functions through an injectionToken.

export type ModelJSONTransformFn<T> = (modelJSON: T) => T;

export type DynamicFormControlJSONTransformFnArray<T = any> = ModelJSONTransformFn<T>[];
export const DYNAMIC_FORM_CONTROL_JSON_TRANSFORM_FN_ARRAY = new InjectionToken<DynamicFormControlJSONTransformFnArray>(
  'DYNAMIC_FORM_CONTROL_JSON_TRANSFORM_FN_ARRAY'
);

usage:

export const DynamicFormControlJSONTransformFnArrayProvider: Provider = {
	provide: DYNAMIC_FORM_CONTROL_JSON_TRANSFORM_FN_ARRAY,
	useValue: [
		/* transform function here */
	]
};

@NgModule({
	...,
	imports: [
		...,
		ReactiveFormsModule,
		DynamicFormsCoreModule
	],
	providers: [
		...,
		DynamicFormControlJSONTransformFnArrayProvider
	]
})
export class AppModule {}

Motivation behind this feature:

Imagine that the form config contains all the labels and text as a path to a translation key.
With this feature, I'm able to Inject an array of transform functions, the first translate all the keys and the second one add an asterisk to the label if the model has required validator.

export const DynamicFormControlJSONTransformFnArrayProvider: Provider = {
	provide: DYNAMIC_FORM_CONTROL_JSON_TRANSFORM_FN_ARRAY,
	useFactory: translateService => ([
		translateKeys(translateService),
		addRequiredAsteriskToLabel()
	]),
	deps: [TranslateService]
};

[codecov-io]

Codecov Report

Merging #1010 into development will decrease coverage by 0.01%.
The diff coverage is 87.5%.

@@              Coverage Diff               @@
##           development   #1010      +/-   ##
==============================================
- Coverage        91.62%   91.6%   -0.02%     
==============================================
  Files              154     154              
  Lines             2293    2300       +7     
  Branches           236     237       +1     
==============================================
+ Hits              2101    2107       +6     
  Misses             135     135              
- Partials            57      58       +1

Impacted Files	Coverage Δ
.../ng-dynamic-forms/core/src/lib/utils/json.utils.ts	100% <100%> (ø)	⬆️
...forms/core/src/lib/service/dynamic-form.service.ts	92.25% <85.71%> (-0.36%)	⬇️

---

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[udos86]

@ronnetzer Thank you very much for this PR!

Please give a bit of time to review this. Thanks again

[ronnetzer]

@udos86 Tried really hard to improve the coverage but I have no idea why it doesn't work :(

[ronnetzer]

@udos86 any news? would love to see this PR merged :)

[matheo]

Hi @ronnetzer
Do you mind to share your experience with dynamic forms
in the discussions of a new library to implement advanced features?
https://dev.to/myndpm/a-new-approach-to-have-dynamic-forms-in-angular-5d11
Thanks in advance!