SimpleValidator

A simple .Net validation library written in C#

It's based largely on the FluentValidation libary with some changes in it's usage.

Why SimpleValidator?

I needed a validation library that satisfied the following criteria:

• Quick and simple validation checks
• Complex business rule validation
• Multiple stages of validation (i.e. do the simple stuff first, then more complex validation, but don't bother with the complex stuff if the simple stuff fails)
• Avoid attribute based validation (I try to avoid using attributes. People think, I've validated my MVC model so my service method should be good to go. Not the case. Service methods should always validate everything as you cannot guarantee validation has been performed)
• Readable
• Central

What I came up with was the following...

As there is quite a bit to cover I'm going to start simply, and add complexity.

Structure

There is 2 types of validation you can perform using SimpleValidator. Extension methods and Validator. The validator essentially uses the extension methods behind the scenes but provides a useful wrapper for doing your validations and groups the error messages in a meaningful way.

Extension methods

As a start, there are some simple extension method you can use.

Include the following using statement:

using SimpleValidator.Extensions;

Then you should have some useful helper methods as shown below:

string email = "[email protected]";

if (email.IsLength(5)) ...
if (email.IsEmail()) ...
if (email.IsMatch("[email protected]")) ...
if (email.IsInt()) ...
if (email.IsNumber()) ...

The full list of extension methods is as follows:

// string based extension methods (IsNotNullOrEmpty and IsNotNullOrWhiteSpace are the only methods that have inverse tests. The assumption is to always assume the positive.
[string].IsNotNullOrEmpty
[string].IsNullOrEmpty
[string].IsNotNullOrWhiteSpace
[string].IsNullOrWhiteSpace();
[string].IsBetweenLength
[string].IsMaxLength
[string].IsMinLength
[string].IsExactLength
[string].IsEmail
[string].IsPassword
[string].IsCreditCard
[string].IsEqualTo

// object based extension methods
[object].IsNotNull
[object].IsNull
[object].Is
[object].IsNot
[object].IsRule // validating against an interface for more complex business rules
[object].IsInt
[object].IsShort
[object].IsLong
[object].IsDouble
[object].IsBool
[object].IsNumber
[object].Is<T>

// integer (same dor double, decimal, short and long)
[integer].IsNotZero
[integer].IsEqualTo
[integer].IsGreaterThan
[integer].IsLessThan
[integer].IsBetween

// datetime
[datetime].IsDate
[datetime].IsGreaterThan
[datetime].IsGreaterThanOrEqualTo
[datetime].IsLessThan
[datetime].IsLessThanOrEqualTo
[datetime].IsEqualTo
[datetime].IsBetween
[datetime].IsGreaterThanDateOnly
[datetime].IsGreaterThanOrEqualToDateOnly
[datetime].IsLessThanDateOnly
[datetime].IsLessThanOrEqualToDateOnly
[datetime].IsEqualToDateOnly
[datetime].IsBetweenDateOnly

From here you also have access to some helpful conversion methods, e.g.

string input = "5";

if (input.IsInt())
    return input.ToInt();

A full list of these are as follows

.ToInt()
.ToShort()
.ToLong()
.ToDouble()
.ToDecimal()
.ToBool()

// and then a more generic one
.To<T>()

Validator

Extension methods work great for quick simple checks, but you probably want to do more complex validation.

For this, lets create a Validator object. From there you can use it to validate several properties of an object with a few overrides as shown below

Remember to include using SimpleValidator;

For each text method you have the following overrides:

SimpleValidator.Validator validator = new Validator();

// value
validator.IsEmail("[email protected]");

// name, value
validator.IsEmail("Email", "[email protected]");

// name, value, message
validator.IsEmail("Email", "[email protected]", "Please enter a valid email address");

if (validator.IsValid())
{
    // everything is good
}
else
{
    // validator.Errors contains a name / message dictionary of your errors 
}

It supports chaining so you could write it as follows

validator
  .IsEmail("[email protected]")
  .IsEmail("Email", "[email protected]", "This is an error message")
  .IsEmail("Email", "[email protected]").WithMessage("This is an error message")

This is quite usefull for more complex object validation e.g.

// validate the name
validator
    .NotNull(name).WithMessage("Name cannot be an empty string")
    .IsLength(name, 5).WithMessage("Name must be at least 5 characters long")
    .IsLength(name, 5, 20).WithMessage("Name must between 5 and 20 characters")
    .Must(() =>
        {
            return name.Contains("abc");
        }).WithMessage("Name cannot contain abc")
    .MustNot(() =>
        {
            return name.Contains("bob");
        }).WithMessage("Name cannot contain bob");

Each of the messages are added to an Error collection within the validator object. It also has a IsValid property. The validation is done as the method is called, which means you can stagger the validation if needed e.g.

string name = "Gordon";

// validate the name
validator
    .NotNull(name).WithMessage("Name cannot be an empty string");

if (validator.IsValid)
{
    // do something here that is dependant on name not being null

    validator.Must(() =>
    {
        // some other condition
        return true;
    });

    if (validator.IsValid)
    {
        // and down the rabit hole we go...
    }
}

IRule

For more complex validation you can use the Is and IsNot validation methods passing in a function which should return a bool. For more serious business rule validations, you can pass in any object implementing the IRule interface to the IsRule(...) method. All this combined gives you some flexibility on how you go about implementing your validation.

Point is, every service method should implement validation for every incoming model.

Ok, I have validation errors, now what?

Implementation

Let's say we have a method

private User AddUser(UserModel user)
{
}

You pass in a UserModel, and if all goes well, the user is added and it returns a User object.

What happens if we encounter validation errors? Once approach is to throw an exception (Not ideal but works) and the library has an exception ready for this.

ValidationException

try
{
    // ...
    ServiceManager.AddUser(model);
    // ...
}
catch (ValidationException ex)
{
    // validation error - The validator is passed in as part of the exception so you can access the errors ex.Validator.Errors
}
catch (Exception ex)
{
    // something else... woops
}

And in your validation method.

private User AddUser(UserModel user)
{
    Validator validator = new Validator();
    // validation happens here...
    
    if (!validator.IsValid)
    {
        validator.ThrowValidationException();
    }

    // or you can do this without the IsValid check (it checks it internally)
    validator.ThrowValidationExceptionIfInvalid();
}

ValidationMethodResult

Another approach is to use the ValidationMethodResult. Changing the above code it now looks as follows

public ValidationMethodResult<User> AddUser(UserModel model)
{
    Validator validator = new Validator();

    // do validation

    return new ValidationMethodResult<User>(validator, user);
}

And then in your calling method

try
{
    // ...
    var result = ServiceManager.AddUser(model);
    
    if (result.IsValid())
    {
        // all good and you have access to the return user
        return Content(result.Result.Name); // The return users name...
    }
    else
    {
        // show errors using result.Errors
    }

    // ...
}
catch (Exception ex)
{
    // something else... woops
}

It's a cleaner approach, allows you to specify complex return types and provides a boolean indication reflecting the validation state of the current object. You could use simple out param's and use a boolean return type for all methods, but I'm not a fan (That doesn't mean it's not right)