How to Validate FormArray length in angular2

Question

I have a data driven form in angular2 like below

this.formBuilder.group({
  \'name\': [\'\',Validators.required],
  \'description\': [\'\', Validators.required],         


        

Answer 1

because you using wrong validator function name: minlength -> minLength

demo code:

import { Component, OnInit } from '@angular/core';
import { FormBuilder, FormGroup, FormArray, Validators } from '@angular/forms';

@Component({
  selector: 'app-root',
  template: `
    <form novalidate [formGroup]="tpForm" (ngSubmit)="onSubmit()">
      <div><input type="text" formControlName="name"></div>
      <div><textarea formControlName="description"></textarea></div>
      <div formArrayName="places">
        <button type="button" (click)="addPlace()">+</button>
        <div *ngFor="let place of places.controls; let i = index">
          <div>
              <span>Places {{i + 1}}</span>
              <button type="button" *ngIf="places.controls.length > 0" 
                  (click)="removePlace(i)">
                  x
              </button>
          </div>
          <input type="text" [formControlName]="i">
        </div>
      </div>
      <button type="submit">Submit</button>
    </form>

    <p>Status: {{ tpForm.valid }}</p>
  `,
  styles: [
    `


    `
  ]
})
export class AppComponent implements OnInit {
  tpForm: FormGroup;

  constructor(private fb: FormBuilder) {}

  ngOnInit() {
    this.tpForm = this.fb.group({
      'name': ['',Validators.required],
      'description': ['', Validators.required],
      'places': this.fb.array([
        this.fb.control('')
      ], Validators.minLength(1))
    })
  }

  get places(): FormArray {
    return this.tpForm.get('places') as FormArray;
  }

  onSubmit() {

  }

  addPlace() {
    this.places.push(this.fb.control(''));
  }

  removePlace(index) {
    this.places.removeAt(index);
  }

}

Plunker: https://plnkr.co/edit/cfi7nN?p=preview

Answer 2

Add this custom validator to your validation service:

minLengthArray(min: number) {
    return (c: AbstractControl): {[key: string]: any} => {
        if (c.value.length >= min)
            return null;

        return { 'minLengthArray': {valid: false }};
    }
}

And then when creating the form do the following:

this.formBuilder.group({
  'name': ['',Validators.required],
  'description': ['', Validators.required],
  'places': this.formBuilder.array([], this.validationService.minLengthArray(1)) 
});

And you can check errors against the FormArray by checking FormArray.hasError('minLengthArray')

Answer 3

Good and clear way to do this is :

Create a Array.validator.ts and put all the custom validations over there , like minLength , maxLength etc

import { ValidatorFn, AbstractControl, FormArray } from '@angular/forms';

// Array Validators
export class ArrayValidators {

    // max length
    public static maxLength(max: number): ValidatorFn | any {
        return (control: AbstractControl[]) => {
            if (!(control instanceof FormArray)) return;
            return control.length > max ? { maxLength: true } : null;
        }
    }

    // min length
    public static minLength(min: number): ValidatorFn | any {
        return (control: AbstractControl[]) => {
            if (!(control instanceof FormArray)) return;
            return control.length < min ? { minLength: true } : null;
        }
    }
}

And Then just import that file and use validation wherever you want to :

import { ArrayValidators } from './array.validator'; // Import it

'hobbies':new FormArray([],ArrayValidators.minLength(2)) // Use it

WORKING DEMO

---

Note :

You can directly use this package also ng-validator ( Reference is taken from this package ) , But If you need just required array validations you can do it like above.

Answer 4

if you are trying to add validation to formarray try this may help you,

this.formBuilder.group({
  'name': ['',Validators.required],
  'description': ['', Validators.required],
  'places': this.formBuilder.array(this.initPlaces()) 
})

initPlaces() {       
        return this._fb.group({
            places: ['',[Validators.minLength(1)]]           
        });
  }

this initPlaces will simply return formGroup with validation as per requirement.

Answer 5

Having a template

<div formArrayName="items">
    <div *ngFor="[...] let i = index" [formGroupName]="i">

    [...]

    </div>
</div>

You could simply use this in your button :

[disabled]="!myForm.get('items.1')"

Answer 6

Validators.required does the magic for you:

// using required 

this.formGroup = this.formBuilder.group({
    taskTreeId: [Common.UID()],
    executionProgrammedTime: ["", [Validators.required]],
    description: [""],
    tasks: this.formBuilder.array([], Validators.required)
});  

// using custom validation

export const minLengthArray = (min: number) => {
  return (c: AbstractControl): {[key: string]: any} => {
    if (c.value.length >= min)
      return null;

    return { MinLengthArray: true};
  }
}

 this.formGroup = this.formBuilder.group({
        taskTreeId: [Common.UID()],
        executionProgrammedTime: ["", [Validators.required]],
        description: [""],
        tasks: this.formBuilder.array([], minLengthArray(2))
    });

<button type="button" class="btn btn-success btn-rounded" 
    [disabled]="!formGroup.valid">SAVE</button>