NGX Form Resolver

A simple library for mapping objects to Angular FormGroups with reusable resolver functions.

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Links

• 🏃 Demo Site w/ Examples
• ⚡ Stackblitz Interactive Example
• 🗄 Changelog

Table of Contents

• Installation
• Quick Start
• API
• Form Resolver Concept
• Form Control Resolver Concept

Installation

npm install ngx-form-resolver --save

Quick Start

1.) Import the FormResolverModule:

@NgModule({
    ...
    imports: 
        ...
        FormResolverModule.forRoot(),
    ]
    ...
})

2.) Inject the FormResolverBuilder (and FormBuilder):

@Component({...})
export class CarFormComponent {
    constructor(private FormResolverBuilder: FormResolverBuilder, private formBuilder: FormBuilder ...) {...}
}

3.) A FormResolver is designed to map a defined class/object to a certain FormGroup. A basic Car class and FormGroup will be used in this example.

export class Car {
    make: string = '';
    model: string = '';
    year: number = null;
    packages = {
        sport: false
    }
}

this.carFormGroup = formBuilder.group({
    'make': [''],
    'model': [''],
    'year': [null],
    'sportPackageCheckbox': [false]
});

4.) Build a FormResolver<Car> with the class and FormGroup:

this.carFormResolver = this.formResolverBuilder
    .setFactory(() => new Car())
    .setFormGroup(this.carFormGroup)
    .setResolvers({
        'make': FormControlResolvers.simple,
        'model': FormControlResolvers.simple,
        'year': FormControlResolvers.simpleNumber,
        'sportPackageCheckbox': FormControlResolvers.nested('packages.sport')
    })
    .build();

5.) Subscribe to changes via observable:

this.carFormResolver.getFormState()
    .pipe(...)
    .subscribe((car: Car) => {...})

6.) Set the value of the form state on demand:

this.carFormResolver.setFormState({
        make: 'Ford';
        model: 'Escape';
        year: 2018;
    } as Car);

7.) Finally, complete OnDestroy:

ngOnDestroy() {
    this.carFormResolver.complete();
}

API

FormResolverBuilder

Service used to build a FormResolver.

• setFactory(factory: Function)
• setFormGroup(formGroup: FormGroup)
• setResolvers(resolverConfig: { [key: string]: FormControlResolver<any> })
• build()

FormResolver

Method	Description
setFormState(object: T)	pass an object to resolve to the form state
getFormState(): Observable<T>	get an observable that returns the resolved form state as an object whenever changes occur
getFormStateSnapshot(): T	get the current resolved form state object
updateFactory(factory: Function)	set a new factory function
updateResolverConfig(resolverConfig: { [key: string]: FormControlResolver<any> })	pass in a completely new config of formControlNames and resolvers
addControl(controlName: string, formControlResolver: FormControlResolver<any>)	adds a control to be watched and resolved
updateControl(controlName: string, formControlResolver: FormControlResolver<any>)	alias to addControl
removeControl(controlName: string)	removes a control from being watched and resolved
complete()	completes all form resolver subjects

FormControlResolver

FormControlResolver type definition:

class FormControlResolver<T> {
    inputResolver: InputResolver<T>;
    outputResolver: OutputResolver<T>;
    ...
}

type InputResolver<T> = (inputObject: T, controlName?: string) => any;

type OutputResolver<T> = (outputObject: T, formValues: any, controlName?: string) => T;

Included default FormControlResolvers:

Resolver	Description
FormControlResolvers.simple	Used for directly mapping the value of a FormControl to a prop of the same name
FormControlResolvers.simpleNumber	The simple formControlResolver except the input & output values are cast as a number
FormControlResolvers.simpleString	The simple formControlResolver except the input & output values are cast as a string
FormControlResolvers.nested(propertyPath: string \| string[])	Used for mapping the value of a FormControl to a nested prop using a . notated string or array of prop strings
FormControlResolvers.nestedNumber(propertyPath: string \| string[])	The nested formControlResolver except the input & output values are cast as a number
FormControlResolvers.nestedString(propertyPath: string \| string[])	The nested formControlResolver except the input & output values are cast as a string

Form Resolver Concept

A FormResolver<T> maps values to a FormGroup from an instance of T and to an instance of T from a FormGroup. A FormResolver is a configuration of FormControlResolvers that define and abstract away control value mapping. Once configured, a FormResolver serves as an adapter between your class/object and FormGroup. A FormResolver is built from the three items below using the FormResolverBuilder service:

• Factory: The base object a FormResolver will use to map form state to. Ultimately, the result of this factory is the base object a FormGroup's state will be resolved into.

• FormGroup: The FormGroup a FormResolver will be mapping to and from.

• ResolverConfig: A config used to map specific FormControls to FormControlResolvers using formControlNames (see below).

Each of these items can be changed at any time using the provided API methods. After building a FormResolver the state of the form can be accessed directly as a snapshot or over time as an observable. The state can also be set using an object or instance of the defined class.

TIPS:

• When passed a null value, a FormResolver will reset the target mapped control
• FormResolvers work with nested FormGroups - both the parent group or any of the child groups.
• Setting properties that are not in your form in your factory's return object will ensure the output form state contains those values (useful when you need keep the values of props not in your form)

Form Control Resolver Concept

Input/Output Resolvers

A FormControlResolver is a reusable, easily testable pair of functions used to map one form control to and from the target object/class. An InputResolver function maps an object to a form and an OutputResolver function maps a form control value to an object.

An InputResolver is passed the object being mapped and the name of the control the resolver is trying to map it to. The return value of this function is the value that the target FormControl will be set to.

An OutputResolver is passed the object being mapped, the full list of values in the formGroup, and the name of the control that needs to be mapped to the object.

Default Form Control Resolvers

There are a few default simple FormControlResolvers that are exported under FormControlResolvers (see API). These FormControlResolvers let you easily map form control values directly to object properties of the same name.

TIPS:

• It can sometimes be useful to create custom a FormControlResolver factory by wrapping it in a function that returns a FormControlResolver. See the example below:

const exampleControlResolverFactory = (value: any) => new FormControlResolver(
    (inputObject: any, controlName: string) => { ... },
    (outputObject: any, formValues: any, controlName: string) => { ... }
)