How can I specify a subset within an Angular FormGroup?

Question

How can I specify a subset within an Angular FormGroup?

Let's consider a scenario:

I have two forms, form1 and form2, each containing multiple FormControls. The common property among them is the FormControl with an id.

Now, I need to pass these forms as arguments to a method that should only require knowledge of the id property.

How can I specify the parameter type for myMethod()? I want to ensure that the parameter for myMethod is a FormGroup with a FormControl named id, along with any other optional FormControls. I attempted using

FormGroup<{id: FormControl}>

, but it resulted in an error:

TS2345: Argument of type 'FormGroup<{ id: FormControl<any>; name: FormControl<any>; }>' is not assignable to parameter of type 'FormGroup<{ id: FormControl<any>; }>'.
Property 'name' is missing in type '{ id: FormControl<any>; }' but required in type '{ id: FormControl<any>; name: FormControl<any>; }'.

What would be the correct way to define the type for the form with just the id field?

export class AppComponent {
  readonly form1 = new FormGroup({
    id: new FormControl(),
    name: new FormControl(),
  });
  readonly form2 = new FormGroup({
    id: new FormControl(),
    title: new FormControl(),
  });

  ngOnInit(): void {
    this.myMethod(this.form1); // Throws error
    this.myMethod(this.form2); // Throws error
  }

  myMethod(form: FormGroup<{id: FormControl}>) {
    // do something
  }
}

angular typescript

Answer 1

Answer №1

utilize the AbstractControl method

execute(control:AbstractControl)
{
    console.log(control.get('id').value)

    //Another option is to "convert" to formGroup
    const formGroup=control as FormGroup

}

Answer 2

utilize the AbstractControl method

execute(control:AbstractControl)
{
    console.log(control.get('id').value)

    //Another option is to "convert" to formGroup
    const formGroup=control as FormGroup

}

Answer 3

Answer №2

There are various approaches, each with its own strengths and weaknesses.

1. Mapped Type

The method I prefer is as follows:

myMethod(form: MyForm) {
  const id = form.controls.id //works.
}

interface MyForm extends FormGroup<{id: FormControl}> {
  [key: string]: any;
}

This approach is clear, concise, easy to understand, and generally effective in most scenarios. It essentially communicates, "We're utilizing a

FormGroup<{id: FormControl}>

, but there may be additional properties we're not concerned with."

2. Partial

If you desire a straightforward one-liner that provides auto-completion for form.controls.id without generating errors, this method also works reasonably well. However, it lacks complete type safety since all properties are considered optional, which could potentially lead to issues. As such, I would recommend it only for quick-and-dirty solutions.

myMethod(form: Partial<FormGroup<{id: FormControl}>>) {
   const id = form.controls.id //works.
}

//Examples:
myMethod('test') // This won't work as it has no similarities with a FormGroup<{id: FormControl}>
myMethod({valid:true}) // This works because all parameters are optional and at least one property matches what a FormGroup<{id: FormControl}> contains.

Answer 4

There are various approaches, each with its own strengths and weaknesses.

1. Mapped Type

The method I prefer is as follows:

myMethod(form: MyForm) {
  const id = form.controls.id //works.
}

interface MyForm extends FormGroup<{id: FormControl}> {
  [key: string]: any;
}

This approach is clear, concise, easy to understand, and generally effective in most scenarios. It essentially communicates, "We're utilizing a

FormGroup<{id: FormControl}>

, but there may be additional properties we're not concerned with."

2. Partial

If you desire a straightforward one-liner that provides auto-completion for form.controls.id without generating errors, this method also works reasonably well. However, it lacks complete type safety since all properties are considered optional, which could potentially lead to issues. As such, I would recommend it only for quick-and-dirty solutions.

myMethod(form: Partial<FormGroup<{id: FormControl}>>) {
   const id = form.controls.id //works.
}

//Examples:
myMethod('test') // This won't work as it has no similarities with a FormGroup<{id: FormControl}>
myMethod({valid:true}) // This works because all parameters are optional and at least one property matches what a FormGroup<{id: FormControl}> contains.

Answer 5

Answer №3

Summary: View a live example demonstrating interface extension in TypeScript.

No magic tricks required, simply declare and extend the appropriate interfaces to achieve this functionality.

This solution is effective because the myMethod function utilizes { controls: IBaseForm } instead of directly using FormGroup, allowing for specific parameter requirements without additional constraints. Additionally, each instance of FormGroup possesses a distinct interface definition (no inferred types used).

Start by ensuring that both forms share a common property where they intersect, such as id:

// Declaring and extending a shared interface is recommended but not mandatory; individual properties can be declared separately
export interface IBaseForm {
  id: FormControl<number>;
}
export interface IForm1 extends IBaseForm {
  name: FormControl<string>;
}
export interface IForm2 extends IBaseForm {
  title: FormControl<string>;
}

export class AppComponent {
  readonly form1: FormGroup<IForm1> = new FormGroup({ id... });
  readonly form2: FormGroup<IForm2> = new FormGroup({ id... });

  ngOnInit(): void {
    this.myMethod(this.form1); // No errors
    this.myMethod(this.form2); // No errors
  }

  myMethod(form: { controls: IBaseForm }) {
    console.log('>> id: ', form.controls.id.value);
  }
}

By observing the screenshot below, it's evident that only the id control is accessible: https://i.sstatic.net/nC3jP.png

Answer 6

Summary: View a live example demonstrating interface extension in TypeScript.

No magic tricks required, simply declare and extend the appropriate interfaces to achieve this functionality.

This solution is effective because the myMethod function utilizes { controls: IBaseForm } instead of directly using FormGroup, allowing for specific parameter requirements without additional constraints. Additionally, each instance of FormGroup possesses a distinct interface definition (no inferred types used).

Start by ensuring that both forms share a common property where they intersect, such as id:

// Declaring and extending a shared interface is recommended but not mandatory; individual properties can be declared separately
export interface IBaseForm {
  id: FormControl<number>;
}
export interface IForm1 extends IBaseForm {
  name: FormControl<string>;
}
export interface IForm2 extends IBaseForm {
  title: FormControl<string>;
}

export class AppComponent {
  readonly form1: FormGroup<IForm1> = new FormGroup({ id... });
  readonly form2: FormGroup<IForm2> = new FormGroup({ id... });

  ngOnInit(): void {
    this.myMethod(this.form1); // No errors
    this.myMethod(this.form2); // No errors
  }

  myMethod(form: { controls: IBaseForm }) {
    console.log('>> id: ', form.controls.id.value);
  }
}

By observing the screenshot below, it's evident that only the id control is accessible: https://i.sstatic.net/nC3jP.png

How can I specify a subset within an Angular FormGroup?

Answer №1

Answer №2

1. Mapped Type

2. Partial

Answer №3

Summary: View a live example demonstrating interface extension in TypeScript.

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