如何解决如何为角形反应形式的形式值添加自定义唯一验证器？
我想添加一个自定义的唯一验证器，它将验证所有标签字段的值都是唯一的。 （I）当我更改表单值时，this.form的值会在 CustomValidator.uniqueValidator（this.form）中传递后更改。如何解决这个问题？ （II）有没有不用任何包装的方法吗？
注意：表单在加载时具有默认值。这是屏幕截图。
this.form = this.fb.group({
fields: this.fb.array([])
});
private addFields(fieldControl?) {
return this.fb.group({
label: [
{value: fieldControl ? fieldControl.label : '',disabled: this.makeComponentReadOnly},[
Validators.maxLength(30),CustomValidator.uniqueValidator(this.form)
]],isRequired: [
{value: fieldControl ? fieldControl.isRequired : false,disabled: this.makeComponentReadOnly}],type: [fieldControl ? fieldControl.type : 'text']
});
}
static uniqueValidator(form: any): ValidatorFn | null {
return (control: AbstractControl): ValidationErrors | null => {
console.log('control..: ',control);
const name = control.value;
if (form.value.fields.filter(v => v.label.toLowerCase() === control.value.toLowerCase()).length > 1) {
return {
notUnique: control.value
};
} else {
return null;
}
}; }
解决方法
在现实生活中，用户名或电子邮件属性被检查为唯一。这将是一个很长的答案，希望您能继续。我将展示如何检查用户名的唯一性。
要检查数据库，您必须创建一个服务以发出请求。因此此验证器将为异步验证器，并将其编写为类。此类将通过依赖项注入技术与服务进行通信。
首先需要设置HttpClientModule。在app.module.ts
import { HttpClientModule } from '@angular/common/http';
@NgModule({
declarations: [AppComponent],imports: [BrowserModule,YourOthersModule,HttpClientModule],providers: [],bootstrap: [AppComponent],})
然后创建服务
ng g service Auth //named it Auth
在此auth.service.ts中
import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
@Injectable({
providedIn: 'root',})
export class AuthService {
constructor(private http: HttpClient) {}
userNameAvailable(username: string) {
// avoid type "any". check the response obj and put a clear type
return this.http.post<any>('https://api.angular.com/username',{
username:username,});
}
}
现在创建一个类ng g class UniqueUsername并在该类中：
import { Injectable } from '@angular/core';
import { AsyncValidator,FormControl } from '@angular/forms';
import { map,catchError } from 'rxjs/operators';
import { of } from 'rxjs';
import { AuthService } from './auth.service';
// this class needs to use the dependency injection to reach the http client to make an api request
// we can only access to http client with dependecny injection system
// now we need to decorate this class with Injectable to access to AuthService
@Injectable({
providedIn: 'root',})
export class UniqueUsername implements AsyncValidator {
constructor(private authService: AuthService) {}
//this will be used by the usernamae FormControl
//we use arrow function cause this function will be called by a
different context,but we want it to have this class' context
because this method needs to reach `this.authService`. in other
context `this.authService` will be undefined.
// if this validator would be used by the FormGroup,you could use
"FormGroup" type.
//if you are not sure you can use type "control: AbstractControl"
//In this case you use it for a FormControl
validate = (control: FormControl) => {
const { value } = control;
return this.authService.userNameAvailable(value).pipe(
//errors skip the map(). if we return null,means we got 200 response
code,our request will indicate that username is available
//catchError will catch the error
map(() => {
return null;
}),catchError((err) => {
console.log(err);
//you have to console the error to see what the error object is. so u can
set up your logic based on properties of the error object.
// i set as err.error.username as an example. your api server might
return an error object with different properties.
if (err.error.username) {
//catchError has to return a new Observable and "of" is a shortcut
//if err.error.username exists,i will attach `{ nonUniqueUsername: true }`
to the formControl's error object.
return of({ nonUniqueUsername: true });
}
return of({ noConnection: true });
})
);
};
}
到目前为止，我们已经处理了服务和异步类验证器，现在我们在表单上实现了它。我将只有用户名字段。
import { Component,OnInit } from '@angular/core';
import { FormGroup,FormControl,Validators } from '@angular/forms';
import { UniqueUsername } from '../validators/unique-username';
@Component({
selector: 'app-signup',templateUrl: './signup.component.html',styleUrls: ['./signup.component.css'],})
export class SignupComponent implements OnInit {
authForm = new FormGroup(
{
// async validators are the third arg
username: new FormControl(
'',[
Validators.required,Validators.minLength(3),Validators.maxLength(20),Validators.pattern(/^[a-z0-9]+$/),],// async validators are gonna run after all sync validators
successfully completed running because async operations are
expensive.
this.uniqueUsername.validate
),},{ validators: [this.matchPassword.validate] }
);
constructor(
private uniqueUsername: UniqueUsername
) {}
//this is used inside the template file. you will see down below
showErrors() {
const { dirty,touched,errors } = this.control;
return dirty && touched && errors;
}
ngOnInit(): void {}
}
最后一步是向用户显示错误：在表单组件的模板文件中：
<div class="field">
<input formControl="username" />
<!-- this is where you show the error to the client -->
<!-- showErrors() is a method inside the class -->
<div *ngIf="showErrors()" class="ui pointing red basic label">
<!-- authForm.get('username') you access to the "username" formControl -->
<p *ngIf="authForm.get('username').errors.required">Value is required</p>
<p *ngIf="authForm.get('username').errors.minlength">
Value must be longer
{{ authForm.get('username').errors.minlength.actualLength }} characters
</p>
<p *ngIf="authForm.get('username').errors.maxlength">
Value must be less than {{ authForm.get('username').errors.maxlength.requiredLength }}
</p>
<p *ngIf="authForm.get('username').errors.nonUniqueUsername">Username is taken</p>
<p *ngIf="authForm.get('username').errors.noConnection">Can't tell if username is taken</p>
</div>
</div>
您可以在父元素（ngModelGroup 或表单本身）上创建一个验证器指令：
import { Directive } from '@angular/core';
import { FormGroup,ValidationErrors,Validator,NG_VALIDATORS } from '@angular/forms';
@Directive({
selector: '[validate-uniqueness]',providers: [{ provide: NG_VALIDATORS,useExisting: UniquenessValidator,multi: true }]
})
export class UniquenessValidator implements Validator {
validate(formGroup: FormGroup): ValidationErrors | null {
let firstControl = formGroup.controls['first']
let secondControl = formgroup.controls['second']
// If you need to reach outside current group use this syntax:
let thirdControl = (<FormGroup>formGroup.root).controls['third']
// Then validate whatever you want to validate
// To check if they are present and unique:
if ((firstControl && firstControl.value) &&
(secondControl && secondControl.value) &&
(thirdContreol && thirdControl.value) &&
(firstControl.value != secondControl.value) &&
(secondControl.value != thirdControl.value) &&
(thirdControl.value != firstControl.value)) {
return null;
}
return { validateUniqueness: false }
}
}
您可能可以简化该检查，但我认为您明白这一点。 我没有测试这段代码，但如果你想看一看，我最近对这个项目中的 2 个字段做了类似的事情：
不用说，像这样的自定义验证器是相当特定于业务的，并且在大多数情况下难以重复使用。更改表单可能需要更改指令。还有其他方法可以做到这一点，但这确实有效，而且是一个相当简单的选择。
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