Angular 5 - Dynamic form validation using template driven form

Question

I am creating form fields dynamically with ngFor and each field is having unique name attr. I am struggling in their validation. My sample code:

<div *ngFor="let dimension of lstShippingDimensions; let i = index" class="dimension-item">
        <input type="text" name="units-{{i}}" [(ngModel)]="dimension.units" 
        class="first-f" placeholder="# of units" required>
        <input type="text" name="width-{{i}}" [(ngModel)]="dimension.width" 
        class="second-f" placeholder="W" required>
        <input type="text" name="height-{{i}}" [(ngModel)]="dimension.height" 
        class="third-f" placeholder="H" required>
        <input type="text" name="length-{{i}}" [(ngModel)]="dimension.length" 
        class="forth-f" placeholder="L" required>
        <select class="five-f" name="unitType-{{i}}" [(ngModel)]="dimension.unitType" 
        required>
            <option>inches</option>
            <option>feet</option>
        </select>
        <div *ngIf="!units-{{i}}.valid && units-{{i}}.touched" class="text-danger text-left">
            <small *ngIf="units-{{i}}.errors.required">Field is required.</small>
        </div>
    </div>

Abdul Rafay · Accepted Answer · 2018-07-20 13:40:45Z

somehow resolved this with just adding #units="ngModel". I guess Angular is handling the referencing in ngFor itself. This works perfectly fine:

<div *ngFor="let dimension of lstShippingDimensions; let i = index" class="dimension-item">
    <input type="text" name="units-{{i}}" #units="ngModel" [(ngModel)]="dimension.units" class="first-f" placeholder="# of units" required>
    <input type="text" name="width-{{i}}" [(ngModel)]="dimension.width" class="second-f" placeholder="W" required>
    <input type="text" name="height-{{i}}" [(ngModel)]="dimension.height" class="third-f" placeholder="H" required>
    <input type="text" name="length-{{i}}" [(ngModel)]="dimension.length" class="forth-f" placeholder="L" required>
    <select class="five-f" name="unitType-{{i}}" [(ngModel)]="dimension.unitType" required>
        <option>inches</option>
        <option>feet</option>
    </select>
    <div *ngIf="!units.valid && units.touched" class="text-danger text-left">
        <small># of units is required.</small>
    </div>
</div>

Tomas · Accepted Answer · 2018-07-20 11:36:59Z

Your example is a use case example of reactive form handling. Please consider using form array and form group:

<form formArrayName="formArray">
<div *ngFor="let dimension of lstShippingDimensions; let i = index" class="dimension-item" [formGroupName]="i">

        <input type="text" name="units-{{i}}" [formControlName]="'units'"
        class="first-f" placeholder="# of units" required>
        <input type="text" name="width-{{i}}" [formControlName]="'width'" 
        class="second-f" placeholder="W" required>
        <input type="text" name="height-{{i}}" [formControlName]="'height'" 
        class="third-f" placeholder="H" required>
        <input type="text" name="length-{{i}}" [formControlName]="'length'" 
        class="forth-f" placeholder="L" required>
        <select class="five-f" name="unitType-{{i}}" [formControlName]="'unitType'" 
        required>
            <option>inches</option>
            <option>feet</option>
        </select>
        <div class="text-danger text-left">
            <small *ngIf="formArrayName[i].errors.required">Field is required</small>
        </div>
    </div>
</form>

Your initial solution did not work, because !units-{{i}}.valid && units-{{i}}.touched" are not exported to template as you expected. It might work if you would declare it as template variable:

    <input type="text" name="height-{{i}}" [(ngModel)]="dimension.height" 
    class="third-f" placeholder="H" required #templateVar="ngForm">
   <div *ngIf="templateVar.valid && templateVar.touched" class="text-danger text-left">
        <small *ngIf="templateVar.errors.required">Field is required.</small>
    </div>

But template variable names can not be created dynamically, i.e. #DynamicVar-{{i}} is not allowed.

Thanks for the reply. The thing is I am restricted to using template driven form as this is just a small part of my form and other fields of my form are dependent on each other. Is there any work around to achieve this?

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