How to implement custom validator in generic validator class angular2?

Question

I am trying implement custom validator into generic validator class, Basically I am aware of that to write normal custom validator in suppurate class but here facing a bit confusion to write in generic validator class. If any one knows please help me out.

Here is my generic-validator.ts file

import { FormGroup } from '@angular/forms';

// Generic validator for Reactive forms
// Implemented as a class, not a service, so it can retain state for multiple forms.
export class GenericValidator {

    // Provide the set of valid validation messages
    // Stucture:
    // controlName1: {
    //     validationRuleName1: 'Validation Message.',
    //     validationRuleName2: 'Validation Message.'
    // },
    // controlName2: {
    //     validationRuleName1: 'Validation Message.',
    //     validationRuleName2: 'Validation Message.'
    // }
    constructor(private validationMessages: { [key: string]: { [key: string]: string } }) {

    }

    // Processes each control within a FormGroup
    // And returns a set of validation messages to display
    // Structure
    // controlName1: 'Validation Message.',
    // controlName2: 'Validation Message.'
    processMessages(container: FormGroup): { [key: string]: string } {
        let messages = {};
        for (let controlKey in container.controls) {
            if (container.controls.hasOwnProperty(controlKey)) {
                let c = container.controls[controlKey];
                // If it is a FormGroup, process its child controls.
                if (c instanceof FormGroup) {
                    let childMessages = this.processMessages(c);
                    Object.assign(messages, childMessages);
                } else {
                    // Only validate if there are validation messages for the control
                    if (this.validationMessages[controlKey]) {
                        messages[controlKey] = '';
                        if ((c.dirty || c.touched) &&
                            c.errors) {
                            for (let messageKey in c.errors) {
                                if (c.errors.hasOwnProperty(messageKey) &&
                                    this.validationMessages[controlKey][messageKey]) {
                                    messages[controlKey] += this.validationMessages[controlKey][messageKey];
                                }
                            }
                        }
                    }
                }
            }
        }
        return messages;
    }
}

Here these are my parameters for custom validator i.e say : '22,3333,4,555,66' , [2,5] first one is comma separated string ... which might have entries of 2 or 5 long Here the condition is each comma suppurated string must be >2.

Answer 1

When I write custom validators it is typically to use with reactive forms. My custom validators are in a class that extends Validators from @angular/forms module. With this, you return null if the validation is good, and an object if it's bad.The following checks for invalid characters.

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

// setup simple regex for white listed characters
const validCharacters = /[^\s\w,.:&\/()+%'`@-]/;

// create your class that extends the angular validator class
export class CustomValidators extends Validators {

 // create a static method for your validation
 static invalidateCharacters(control: FormControl) {

    // first check if the control has a value
    if (control.value && control.value.length > 0) {

      // match the control value against the regular expression
      const matches = control.value.match(invalidCharacters);

      // if there are matches return an object, else return null.
      return matches && matches.length ? { invalid_characters: matches } : null;
    } else {
      return null;
    }
  }
}

Make a FormErrorService that builds up your error message:

import { Injectable } from '@angular/core';
import { FormGroup } from '@angular/forms';

@Injectable()
export class FormErrorService {

  // return list of error messages
  public validationMessages() {
    const messages = {
      required: 'This field is required',
      email: 'This email address is invalid',
      is1980OrLater: 'Please enter a date that is after 01/01/1980.',
      maxDateFailed: (failText: string) => {
        return failText;
      },
      minDateFailed: (failText: string) => {
        return failText;
      },
      invalid_characters: (matches: any[]) => {

        let matchedCharacters = matches;

        matchedCharacters = matchedCharacters.reduce((characterString, character, index) => {
          let string = characterString;
          string += character;

          if (matchedCharacters.length !== index + 1) {
            string += ', ';
          }

          return string;
        }, '');

        return `These characters are not allowed: ${matchedCharacters}`;
      },
    };

    return messages;
  }

  // Validate form instance
  // check_dirty true will only emit errors if the field is touched
  // check_dirty false will check all fields independent of
  // being touched or not. Use this as the last check before submitting
  public validateForm(formToValidate: FormGroup, formErrors: any, checkDirty?: boolean) {
    const form = formToValidate;

    for (const field in formErrors) {
      if (field) {
        formErrors[field] = '';
        const control = form.get(field);

        const messages = this.validationMessages();
        if (control && !control.valid) {
          if (!checkDirty || (control.dirty || control.touched)) {
            for (const key in control.errors) {
              if (key && key !== 'invalid_characters') {
                formErrors[field] = formErrors[field] || messages[key];
              } else {
                formErrors[field] = formErrors[field] || messages[key](control.errors[key]);
              }
            }
          }
        }
      }
    }
    return formErrors;
  }
}

Where you're building the form in your comopnent:

    import {CustomValidators} from 'filepath';
    import {FormErrorService} from 'formerrorservicepath';
    myFormGroup: FormGroup;
    public formErrors = {
    myInput: ''
  };
  formErrors = [];
  constructor(
    public formErrorService: FormErrorService
  ) {}
    // then in your ngOnInit 
    this.myFormGroup = new FormGroup({});
    this.myFormGroup.addControl('myInput', new FormControl());
    this.myFormGroup.get('myInput').setValidators(Validators.compose([CustomValidators.invalidCharacters]);

this.myFormGroup.valueChanges.subscribe(data => {
      this.formErrors = [];
        this.formErrors = this.formErrorService.validateForm(
          this.myFormGroup,
          this.formErrors,
          true
        );
      })

Now in your HTML:

<form [formGroup]="myFormGroup">
<div>
<input type="text" formControlName="myInput"/>
<p *ngFor="let error of formErrors">
{{error}}
</p>
<button type="button" [diabled]="!myFormGroup.valid">Action Button</button>
</div>
</form>

Answer 2

You can try out a framework called ts.validator.fluent. Generic object validation. Fluent rules.

https://github.com/VeritasSoftware/ts.validator

NPM Package:

https://www.npmjs.com/package/ts.validator.fluent

There is also an Angular 6 CLI app to demo the framework:

https://github.com/VeritasSoftware/ts-validator-app-angular6

Here is an example of how your TypeScript models can be validated using the framework:

/* Install npm package ts.validator.fluent and then import like below */
import { IValidator, Validator, ValidationResult } from 'ts.validator.fluent/dist';

/*TypeScript model*/
class Person {
   Name: string;
}

/* Validation rules */
var validatePersonRules = (validator: IValidator<Person>) : ValidationResult => {
   return validator
       .NotEmpty(m => m.Name, "Name cannot be empty")
   .ToResult();
};

/* Populate model */
var person = new Person();
person.Name = "John Doe";

/* Validate model */
/* Sync */
var validationResult = new Validator(person).Validate(validatePersonRules);
/* Async */
var validationResult = await new Validator(person).ValidateAsync(validatePersonRules);