FluentValidationExtensions.AutoMapper 11.0.1

FluentValidation.Extensions.AutoMapper

FluentValidation Extensions for AutoMapper 7, 8 and 11 (and up).

Problem

When the normal MVC validation is defined on a ViewModel and additional validation is done in the business-layer on the dto's using FluentValidation, the error messages are using the property names from the dto instead of the view-model. The following code shows this problem:

ViewModel Example

The flattened Person view model class.

public class Person
{
    [Required]
    public string FirstName { get; set; }

    public string Street { get; set; }

    public string City { get; set; }
}

DTO models example

The PersonDto model class:

public class PersonDto
{
    public string First { get; set; }

    public AddressDto Address { get; set; }
}

The AddressDto model class:

public class AddressDto
{
    public string Street { get; set; }

    public string City { get; set; }
}

When posting an invalid Person object to the WebAPI, you get an error back like (notice that the property names from the DTO are used!):

{
    "First": [
        "no 'a' allowed"
    ],
    "Address.City": [
        "The length of 'City' must be 2 characters or fewer. You entered 3 characters."
    ],
    "Address.Street": [
        "The length of 'Street' must be 3 characters or fewer. You entered 4 characters."
    ]
}

Solution

This library solves this issue by implementing a custom FluentValidation - PropertyNameResolver which uses the AutoMapper mapping definitions to translate the errors with DTO property names into view model errors. Example response will be like:

{
    "City": [
        "The length of 'City' must be 2 characters or fewer. You entered 3 characters."
    ],
    "Street": [
        "The length of 'Street' must be 3 characters or fewer. You entered 4 characters."
    ],
    "FirstName": [
        "no 'a' allowed"
    ]
}

Code Changes

To get this working you need the following changes for a DotNet Core MVC WebAPI project:

1. Install the FluentValidationExtensions.AutoMapper package

dotnet add package FluentValidationExtensions.AutoMapper

2. Dependency Injection Configuration changes

Let the DI framework inject an instance of IMapper into your Configure(...) method. You can then use the injected IMapper to create a new instance from the FluentValidationPropertyNameResolver and assign this to the static ValidatorOptions class.

-public void Configure(IApplicationBuilder app, IHostingEnvironment env)
+public void Configure(IApplicationBuilder app, IHostingEnvironment env, IMapper mapper)
{
     mapper.ConfigurationProvider.AssertConfigurationIsValid();

+    var resolver = new FluentValidationPropertyNameResolver(mapper);
+    ValidatorOptions.PropertyNameResolver = resolver.Resolve;
}

For a complete example, see the code from FluentValidationExample.Web.

Sponsors

Entity Framework Extensions and Dapper Plus are major sponsors and proud to contribute to the development of FluentValidation.Extensions.AutoMapper.