Validation

Structr.AspNetCore.Validation package contains number of attributes supplying a wide range of developer's basic needs in validating user-input data in ASP.NET Core application. Everything is done in classic manner by specifying validation attributes for properties to be validated. Every attribute generates it's own but fully customizable error message. More to say - validation attributes could be combined between each other when you need it.

Inspiration for creating this package was found in validation package for ASP.NET MVC - Foolproof and ASP.NET Core fork - Foolproof.Core.

Installation

AspNetCore.Validation package is available on NuGet.

dotnet add package Structr.AspNetCore.Validation

Setup

Setup validation services in your ASP.NET Core application:

services.AddAspNetCoreValidation();

Usage

Add validation attributes for your models. For example:

public class AddUserViewModel
{
    public string FullName { get; set; }
    public bool IsEmployee { get; set; }

    [RequiredIf(nameof(IsEmployee), true, ErrorMessage = "Employee must have some role.")]
    public IEnumerable<int> RolesIds { get; set; }

    public DateTime? ActiveFrom { get; set; }

    [GreaterThanOrEqualTo(nameof(ActiveFrom), PassOnNull = true)]
    public DateTime? ActiveTo { get; set; }
}

And check ModelState.IsValid property in controller action:

[HttpPost]
public IActionResult AddUser(AddUserViewModel addUserViewModel)
{
    if (ModelState.IsValid == false)
    {
        return View(addUserViewModel);
    }

    /* Some logic here */

    return RedirectToAction("Index");
}

List of properties that are available in each validation attribute:

Property name	Description
RelatedProperty	Value of the related property with which the value of validating property will be compared.
RelatedPropertyDisplayName	Display name of the related property with which value the value of validating property will be compared. Will be used in error message if validation fails.
ErrorMessage	An error message to associate with a validation control if validation fails.
ErrorMessageResourceName	The error message resource name to use in order to look up the ErrorMessageResourceType property value if validation fails.
ErrorMessageResourceType	The resource type to use for error-message lookup if validation fails.

So all attributes allow to specify custom error messages and get them from resource files if needed.

Simple validation

These attributes allow to specify related property which value will be used to check value of marked property.

Attribute name	Description
EqualTo	Specifies that a data field value must be equal to a value of specified related property.
NotEqualTo	Specifies that a data field value must NOT be equal to a value of specified related property.
GreaterThan	Specifies that a data field value must be greater than a value of specified related property.
GreaterThanOrEqual	Specifies that a data field value must be greater or equal to a value of specified related property.
LessThan	Specifies that a data field value must be less than a value of specified related property.
LessThanOrEqualTo	Specifies that a data field value must be less or equal to a value of specified related property.
In	Specifies that a data field value must be contained in value of specified related property. In case of array-type of related property simple inclusion will be checked. If it's not an array-type the equality operator will be used.
NotIn	Specifies that a data field value must NOT be contained in value of specified related property. In case of array-type of related property simple inclusion will be checked. If it's not an array-type the equality operator will be used.
Is	The generalized version of those above. Specifies that a data field value must match a value of specified related property. This one needs a matching Operator to be specified.

In addition to properties available for all validation attributes, attributes of this type has PassOnNull. This property indicates that validation should be passed if value of property to be validated or value of related property equals null. In case of both values are null then the behavior of validation will depend on type of attribute. GreaterThan, LessThan, NotIn and NotEqualTo will fail validation. Others will succeed.

Requirements

These allow to make marked property requirement as conditional and based on related property value.

Attribute name	Description
RequiredIfEmpty	Marks property as required when related property is empty.
RequiredIfNotEmpty	Marks property as required when related property is NOT empty.
RequiredIfTrue	Marks property as required when related property equals true.
RequiredIfFalse	Marks property as required when related property equals false.
RequiredIfRegExMatch	Marks property as required when related property matches provided regular expression.
RequiredIfNotRegExMatch	Marks property as required when related property DOESN'T match provided regular expression.
RequiredIf	The generalized version of attributes above.

Regular expressions

The last one is RegularExpressionIf attribute which allows to check that a data field value must match the specified regular expression but only when related property has specified value.

public class FooViewModel
{
    [RegularExpressionIf("[A-Z][a-z]\\d", nameof(Bar), true)]
    public string Foo { get; set; }

    public bool Bar { get; set; }
}

This one will validate Foo property to match [A-Z][a-z]\d expression only if Bar property will be true.

Client

Use AspNetCore.Validation JavaScript files on client side with jQuery validation plugin:

Client scripts:

Script name	Description
aspnetcore.validation.js	Basic client validation functions.
aspnetcore.jquery.validation.js	Adapters for jQuery validation plugin.
aspnetcore.validation.unobtrusive.js	Adapters for unobtrusive.

<!DOCTYPE html>
<html>
<head>
    <!-- Some HTML here -->
    <!-- jQuery.Validation -->
    <script src="/assets/js/jquery.validation/jquery.validate.js"></script>
    <script src="/assets/js/jquery.validation/jquery.validate.unobtrusive.js"></script>
    <!-- AspNetCore.Validation -->
    <script src="/assets/js/aspnetcore.validation/aspnetcore.validation.js"></script>    
    <script src="/assets/js/aspnetcore.validation/aspnetcore.jquery.validation.js"></script>
    <script src="/assets/js/aspnetcore.validation/aspnetcore.validation.unobtrusive.js"></script>
</body>
</html>

Important: Order of includes client scripts is required!