[Proposal] medatdata / extras property for AbstractControl

[mkurcius]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[ ] Bug report  
[x] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question

Current behavior

Currently there is no way to construct FormControl, FormGroup and FormArray and set metadata / extras info (ex. allowedValues etc.)

Expected behavior

Possibility to set metadata / extras info

What is the motivation / use case for changing the behavior?

Possibility to set metadata info for each specific control would be very helpful when writing forms. For example generating select options would looks like that:

<label for="control1">Control 1</label>
<select id="control1" [formControl]="control1">
  <option *ngFor="let option of control.metadata.allowedValues" [ngValue]="option">
    {{option.someProp}}
  </option>
</select>

<label for="control2">Control 2</label>
<select id="control2" [formControl]="control2">
  <option *ngFor="let option of control.metadata.allowedValues" [ngValue]="option">
    {{option.someProp}}
  </option>
</select>

Or if you have a form which is table but not all cells are controls, let say in each row you have cell with id (it is not a control just value for the user):

<table>
  <thead>
  <tr>
    <th>...</th>
    <th>...</th>
    <th>...</th>
  </tr>
  </thead>
  <tbody>
  <tr *ngFor="let control of controls"
      [formGroup]="control"
      [attr.id]="control.metadata.id">

    <td>{{control.metadata.id}}</td>
    <td><input formControlName="child1"></td>
    <td><input formControlName="child2"></td>
  </tr>
  </tbody>
</table>

And there may be many more usage examples

Proposal API

Setting this new property should be possible by using FormBuilder, FormControl, FormGroup and FormArray:

• for FormBuilder#group pass as optional property in extra arg
• for FormBuilder#array, FormGroup and FormArray pass as 4th optional arg
• for FormBuilder#control and FormControl pass as optional property in formState arg

Example:

formBuilder.group({
  child1: {
    value: null, 
    metadata: { allowedValues: ['A', 'B', 'C'] }
  },
  child2: ''
  array: formBuilder.array([], null, null, {category: 'CUSTOMER_1'})
}, {
  metadata: { id: 1253 }
})

[mkurcius]

Is there any news on this? :)

[kobvel]

Any updates here?

[jorroll]

For those interested, I created a proposal to update ReactiveFormsModule to address a few outstanding issues, including this one (#31963). The proposal is a breaking update (proposed as ReactiveFormsModule2), which is definitely not necessary to address this issue specifically--but I figured folks interested in this issue, and improving the ReactiveFormsModule in general, might have useful feedback.

In addition to adding a data property to AbstractControl (for storing arbitrary data), it also updates the AbstractControl API so all changes to the abstract control are emitted from a changes property (allowing you to subscribe to updates for any abstract control property). It also allows adding arbitrary metadata to any state change emitted from the changes property. This might be useful if you wanted to have special handling of value changes which were triggered by a specific service (as opposed to user input). You can learn more in #31963.

[kdryzek]

It may be achieved by simple extending of FormControl, then each of custom inputs may have its own custom model extending DefaultFormControlModel. However native support for such feature would be highly appreciated.

export interface DefaultFormControlModel<T> {
    value?: T;
    required?: boolean;
    label?: string;
    disabled?: boolean;
    readonly?: boolean;
    asyncValidators?: Validator[];
    validators?: Validator[];
}

export abstract class CustomFormControl<T extends DefaultFormControlModel<T['value']>> extends FormControl {
    public model: T = { } as any;

    protected constructor(defaultFormControlModel: T) {
        super({
                value: defaultFormControlModel.value,
                disabled: !!defaultFormControlModel.disabled,
            },
            getValidators(defaultFormControlModel.validators),
            getAsyncValidators(defaultFormControlModel.asyncValidators),
        );
        Object.assign(this.model, defaultFormControlModel);
    }

    public setModelProperty(name: string, value: any) {
        this.model[name] = value;
    }
}

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[tahir-jamil]

Mata data is a best features when you are creating dynamic reactive forms also where form group is also dynamically created by form controls such as i need to send
productID, attributeId, attributeValue
hear is this example i have to use attribute Value and in from control but as we don't have any mata data option so when submitting the form i don't know what the current AttributeValue is related to What productId or what attribute Id,
We only have the list of Attributes and if the BindValue is id instead of object then we only know the list of ids of attributes which is useless for me unless i assign related id to related productId and AttributeId

Mata data can fix this problem very easily while creating Form Control i can set all mata data related to that object with attributeValue and at the end i have my array of object already set

Please reconsider this feature and add mata data support
Votes are always insufficient because this feature is required we very less frequency but its power frequency is much much higher .

[SoaringColinLaws]

I just ran into a use case in which I need meta data on AbstractControl, all for the same reasons as other users here on this thread. Additional information for the control would allow us to dynamically create forms, without the need to manually create templates every time we need a form. In the meantime, we'll have to find a way to extend or modify Angular's AbstractControl type.