How do I enable validation without using the DataAnnotationValidator?

Create a Blazor application using the link.

Install the “FluentValidation” package using the NuGet package manager.

Create a new folder named FluentValidation in the main application and add the following *.cs files – Employee, EmployeeValidator, FluentValidationValidator to it as shown below.

Add a model Employee class name in the Employee.cs file.

  namespace {AppName}.FluentValidation
   {
       public class Employee
       {
           public string Name { get; set; }
           public string Organization { get; set; }
       }
   }

To write a model validator, you must create a EmployeeValidator class that is inherited from the AbstractValidator<Employee> and then add all the validation rules for the respective model to the constructor.

   using FluentValidation;
    
   namespace {AppName}.FluentValidation
   {
       public class EmployeeValidator : AbstractValidator<Employee>
       {
           public EmployeeValidator()
           {
               RuleFor(p =>   p.Name).NotEmpty().WithMessage("You   must enter a valid name.");
               RuleFor(p =>   p.Name).MaximumLength(20).WithMessage("The   name cannot be more than 20 characters long.");
               RuleFor(p =>   p.Organization).NotEmpty().WithMessage("You   must enter a valid organization name.");
           }
       }
   }

In FluentValidationValidator.cs, create a new validator component named FluentValidationValidator to replace DataAnnonationsValidator, and add the code below to it.
 
The FluentValidationValidator receives an EditContext as a cascading parameter and hooks into the EditContext’s OnFieldChanged and OnValidationRequested events to know when something is happening in the UI. It can add or remove validation messages from a ValidationMessageStore at any time.

using System;
   using FluentValidation;
   using Microsoft.AspNetCore.Components;
   using Microsoft.AspNetCore.Components.Forms;
    
   namespace {AppName}.FluentValidation
   {
       public class FluentValidationValidator<TValidator> : ComponentBase where TValidator :   IValidator, new()
       {
           private readonly static char[] separators = new[] { '.', '[' };
           private TValidator validator;
    
           [CascadingParameter] 
           private EditContext EditContext { get; set; }
    
           protected override void OnInitialized()
           {
               validator = new TValidator();
               var messages = new ValidationMessageStore(EditContext);
    
               /* Re-validate when any field changes or when the entire form   requests validation.*/
               EditContext.OnFieldChanged +=   (sender, eventArgs)
                   =>   ValidateModel((EditContext)sender, messages);
    
               EditContext.OnValidationRequested   += (sender, eventArgs)
                   =>   ValidateModel((EditContext)sender, messages);
           }
    
           private void ValidateModel(EditContext editContext,   ValidationMessageStore messages)
           {
               var context = new ValidationContext<object>(editContext.Model);
               var validationResult =   validator.Validate(context);
               messages.Clear();
               foreach (var error in   validationResult.Errors)
               {
                   var fieldIdentifier =   ToFieldIdentifier(editContext, error.PropertyName);
                   messages.Add(fieldIdentifier,   error.ErrorMessage);
               }
                 editContext.NotifyValidationStateChanged();
           }
    
           private static FieldIdentifier ToFieldIdentifier(EditContext   editContext, string propertyPath)
           {
               var obj =   editContext.Model;
    
               while (true)
               {
                   var nextTokenEnd =   propertyPath.IndexOfAny(separators);
                   if (nextTokenEnd < 0)
                   {
                       return new FieldIdentifier(obj,   propertyPath);
                   }
    
                   var nextToken =   propertyPath.Substring(0, nextTokenEnd);
                   propertyPath =   propertyPath.Substring(nextTokenEnd + 1);
    
                   object   newObj;
                   if (nextToken.EndsWith("]"))
                   {
                       nextToken =   nextToken.Substring(0, nextToken.Length - 1);
                       var prop =   obj.GetType().GetProperty("Item");
                       var indexerType =   prop.GetIndexParameters()[0].ParameterType;
                       var indexerValue =   Convert.ChangeType(nextToken, indexerType);
                       newObj =   prop.GetValue(obj, new object[] { indexerValue });
                   }
                   else
                   {
                       var prop =   obj.GetType().GetProperty(nextToken);
                       if (prop == null)
                       {
                           throw new   InvalidOperationException($"Could not find   property named {nextToken} in object of type {obj.GetType().FullName}.");
                       }
                       newObj =   prop.GetValue(obj);
                   }
    
                   if (newObj == null)
                   {
                       return new FieldIdentifier(obj,   nextToken);
                   }
    
                   obj = newObj;
               }
           }
       }
   }

Add the following code to the Index.razor page to perform fluent validation using the FluentValidationValidator component and its model validator (EmployeeValidator) in the EditForm component.

  @page "/"
    
   @using {AppName}.FluentValidation;
    
   <EditForm Model="employee" OnValidSubmit="SubmitForm">
       <FluentValidationValidator TValidator="EmployeeValidator" />
       <ValidationSummary />
    
       <div class="form-group">
           <label for="name">Name:</label>
           <InputText @bind-Value="employee.Name" class="form-control" id="name" />
       </div>
    
       <div class="form-group">
           <label for="age">Organization:</label>
           <InputText @bind-Value="employee.Organization" class="form-control" />
       </div>
    
       <button type="submit" class="btn btn-primary">Submit</button>
    
   </EditForm>
    
   @code {
       Employee employee { get; set; } = new Employee();
    
       public void SubmitForm()
       {
    
       }
   }

View Sample in GitHub