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

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

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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.