How to Add a Validator dynamically to a FormControl in Angular 2

Question

I am using ReactiveFormsModule and have defined all my form controls including simple validators such as Validators.required within a const configuration.

I wanted to add a custom validator to one of those FormControls.

I have currently added the custom validator as a function within this configuration, and it is working fine, but it does not belong here, it really needs to live within my component, but I'm not sure how I can just attach a custom validator manually after the FormBuilder has configured all my controls.

See Code Comment below that looks like this

How do I Attach Here

* ??? *

this.form.get('site_id').add custom valiator

This is my current configuration code.

import {FormControl, Validators, FormBuilder} from '@angular/forms';

var fb = new FormBuilder();

function exampleValidator(control: FormControl): { [s: string]: boolean} {
    if (control.value === 'Example'){
        return { example: true };
    }

    return null;
}

export const formConfig = fb.group({
  'extract_batch_id': ['bbbbbbbbbbbbb',
    [
       Validators.required
    ]], 
  'site_id': ['blah',
    [
       Validators.required,
        exampleValidator
    ]]
});

I have a directive that really should be storing the custom validator

Job Search Component

import {Component, Input, OnInit, OnDestroy} from '@angular/core';
import {FormGroup, FormControl} from '@angular/forms';
import {ActivatedRoute} from '@angular/router';
import {Subscription} from 'rxjs';

import {Job} from '../../../models/job';
import {JobService} from '../../../services/api/job.service';
import {DebugService} from '../../../common/debug/debug.service';
import {formConfig} from './edit.form-config';

@Component({
    selector: 'wk-job-search-edit',
    template: require('./edit.html')
})
export class JobSearchEditComponent {
    form: FormGroup;

    job: Job;

    @Input() jobId: number;
    private subscription: Subscription;

    constructor(
        private route: ActivatedRoute,
        private jobService: JobService,
        private debug: DebugService){

        // Configure form FormGroup via exported formConfig
        this.form = formConfig;

        // How do I Attach Here
        // *** ??? ***
        // this.form.get('site_id').add custom valiator 
    }

    /*
    exampleValidator(control: FormControl): { [s: string]: boolean} {
        if (control.value === 'Example'){
            return { example: true };
        }

        return null;
    }
    */
}

JobSearch Edit.html

<form [formGroup]="form" (ngSubmit)="onSubmit()">

    <button type="submit" class="btn btn-success" [disabled]="!form.valid">Save</button>
    <div class="form-group" [ngClass]="{'has-danger':!form.get('extract_batch_id').valid}">
        <label for="extract_batch_id" class="form-control-label">Extract Batch</label>
        <input id="extract_batch_id" formControlName="extract_batch_id" type="text" placeholder="Extract Batch" class="form-control input-sm">
        <div *ngIf="!form.get('extract_batch_id').valid">
            <div class="form-control-feedback">Extract Batch is required?</div>
            <small class="form-text text-muted">Please enter a Extract Batch, eg. xyz.</small>
        </div>
    </div>

    <div class="form-group" [ngClass]="{'has-danger':!form.get('site_id').valid}">
        <label for="site_id" class="form-control-label">Site</label>
        <input id="site_id" formControlName="site_id" type="text" placeholder="Site" class="form-control input-sm">
        <div *ngIf="!form.get('site_id').valid">
            <div class="form-control-feedback">Site is required?</div>
            <small class="form-text text-muted">Please enter a Site, eg. xyz.</small>
        </div>
    </div>


</form>

Answer 1

When adding validators dynamically, it's very important to understand the differences between methods:

setValidators - it deletes all current validators, and set up newly provided
addValidators - current validators remain, + newly provided
removeValidators - deletes specific validator
clearValidators - deletes all validators

I had an issue where I was setting dynamically required validator with setValidators, and even though I added before that, conditional logic for adding Pattern validator with addValidator method, it was always getting deleted!

this.toControl.addValidators(Validators.pattern('[a-zA-Z ]*'))
...
this.fromControl.setValidators([Validators.required]); // now we only have required validator

Answer 2

Looking at your code, what you could do:

<div class="form-group" [ngClass]="{'has-danger':!form.get('site_id').valid}">
        <label for="site_id" class="form-control-label">Site</label>
        <input id="site_id" [formControl]="site_id_control" type="text" placeholder="Site" class="form-control input-sm">
        <div *ngIf="!form.get('site_id').valid">
            <div class="form-control-feedback">Site is required?</div>
            <small class="form-text text-muted">Please enter a Site, eg. xyz.</small>
        </div>
    </div>

Look at [formControl]="site_id_control"

Then, this way, you can add or remove the validators from that specific control like this:

inside your class:

export class JobSearchEditComponent {
    private site_id_control=this.form.controls['site_id'];

    updateValidator(){
       let exisitingValidators = this.site_id_control.validators;
       this.site_id_control.setValidators(Validators.compose([...existingValidators , exampleValidator]))

        // you probably also need this : 
         this.site_id_control.updateValueAndValidity();

    }
}