Common Fluent validation usages in web api development
Validation is one of the essential parts of any api development, below will discuss some of the common usage scenarios of Fluentvalidation.
Note: The main idea of this post is to make you familiar with the different usage scenarios of the Fluentvalidation, so we will not discuss much on the dot net core project creation and solution structure. In this solution, we are using the Dependency injection concept, so you are assumed to be familiar with those concepts ahead.
For the demo purpose, I have created a simple web api project in dot net core. Below are the classes and objects used in the project.
- Request Object Customer
- One Service Method Class with Interface (ServiceMethod.cs)
- One Validator Class (CustomerValidator.cs)
- One Controller class (FluentValidationDemo.cs)
- One Enum, Utility, and EnumExtension classes
Prerequisite:
We have to add FluentValidation.AspNetCore package from Nuget.
Once the package is added we can see the reference below:
We have created a dummy customer class object as below to demonstrate different scenarios.
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public class Customer
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public string IdentificationNumber { get; set; }
public string Email { get; set; }
public string Gender { get; set; }
public DateTime? DateOfBirth { get; set; }
public string Mobile { get; set; }
public string Username { get; set; }
public List<Address> AddressList { get; set; }
public List<Document> DocumentList { get; set; }
}
public class Address
{
public string AddressLine1 { get; set; }
public string AddressLine2 { get; set; }
public string PostBox { get; set; }
}
public class Document
{
public int Id { get; set; }
public bool? IsActive { get; set; }
public string DocumentName { get; set; }
public DateTime ExpiryDate { get; set; }
public DateTime CreatedDate { get; set; }
}
All validation functionality will be handled in the CustomerValidator class. From controller we will be calling the validator class as below.
await new CustomerValidator(\_serviceMethods).ValidateAndThrowAsync(customer);
Let us discuss different validation scenarios now:
Empty and Null check for a string field
Field: FirstName
Description: Checks the Firstname field for empty and null cases.
ValidationCode:1 2 3
RuleFor(x => x.FirstName) .NotEmpty() .WithMessage("First name required");
Empty check for nullable field
Field: DateOfBirth
Description: As you know dateofbirth is a nullable field, it checks DateOfBirth for value, please note that NotNull() check will not help in this case.
ValidationCode:1 2 3
RuleFor(x => x.DateOfBirth) .NotEmpty() .WithMessage("Date of birth required");
Validation based on Condition (using When)**
Field: DateOfBirth
Description: Check DateofBirth greater than today’s date when it has value.
ValidationCode:1 2 3 4 5 6 7
When(e => e.DateOfBirth.HasValue, () => { RuleFor(model => model.DateOfBirth.Value.Date) .LessThanOrEqualTo(x => System.DateTime.Today) .WithMessage("Date of birth cannot be greater than todays date."); });
Validation using custom rule and context**
Field: DateOfBirth
Description: Using DateofBirth we check the user is aged 18 years or above otherwise deny. The context object is used to pass the proper validation message
ValidationCode:1 2 3 4 5 6 7 8
RuleFor(model => model.DateOfBirth.Value.Date) .Custom((x, context) => { if (x.AddYears(18) > DateTime.Now) { context.AddFailure($"Users with age less than 18 years not allowed to register, please check DateofBirth {x:dd-MMM-yyyy}"); } });
Validation using Regular Expression**
Field: Email
Description: The format of the email is checked using regular expressions.
ValidationCode:1 2 3 4 5
RuleFor(x => x.Email) .NotEmpty() .WithMessage("Email required") .Matches(@"^\[a-zA-Z0-9.!#$%&’\*+/=?^\_\`{|}~-\]+@\[a-zA-Z0-9-\]+(?:\\.\[a-zA-Z0-9-\]+)\*$") .WithMessage("Email format is wrong.");
Validation using Static method**
Field: Mobile
Description: The business logic is written in a static class, you can write your own logic in the method. In our example, we validate mobile number should start with 04 or 09 and has 10 digits.
ValidationCode:1 2 3 4 5 6 7 8 9 10 11 12 13 14
RuleFor(e => e.Mobile) .NotEmpty() .WithMessage("Mobile number required.") .Must(x => Utility.ValidateMobileNumber(x)) .WithMessage("Mobile number Not Valid"); public static bool ValidateMobileNumber(string userMobile) { bool isValidMobileNumber = false; if (!string.IsNullOrEmpty(userMobile)) isValidMobileNumber = new Regex(@"^0(9|4)\\d{8}$").IsMatch(userMobile); return isValidMobileNumber; }
Validation based on items in enum List**
Field: Gender
Description: Here we use an enum extension function to get the list of enum descriptions and validate whether the gender field value is present in that list when the gender field is not empty.
ValidationCode:1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
//get list of gender types readonly List<string> genderTypes = EnumExtension.GetEnumValuesAndDescriptions<GenderTypes>().Select(c => c.Value).ToList(); //validation When(e => !string.IsNullOrEmpty(e.Gender), () => { RuleFor(e => e.Gender) .Must(x => genderTypes.Contains(x.ToUpper())) .WithMessage($"Gender is invalid, allowed values are {String.Join(",", genderTypes)}"); }); //enum public enum GenderTypes { \[Description("MALE")\] MALE, \[Description("FEMALE")\] FEMALE, \[Description("OTHER")\] OTHER } //enum extesion method public static List<KeyValuePair<string, string>> GetEnumValuesAndDescriptions<T>() { Type enumType = typeof(T); if (enumType.BaseType != typeof(Enum)) throw new ArgumentException("T is not System.Enum"); List<KeyValuePair<string, string>> enumValList = new List<KeyValuePair<string, string>>(); foreach (var e in Enum.GetValues(typeof(T))) { var fi = e.GetType().GetField(e.ToString()); var attributes = (DescriptionAttribute\[\])fi.GetCustomAttributes(typeof(DescriptionAttribute), false); enumValList.Add(new KeyValuePair<string, string>(e.ToString(), (attributes.Length > 0) ? attributes\[0\].Description : e.ToString())); } return enumValList; }
Validation based on two fields in the request model**
Field: Username, Email
Description: Here we check if the email field contains username text when both fields are not empty.
ValidationCode:1 2 3 4 5 6 7
When(e => (!string.IsNullOrEmpty(e.Username) && !string.IsNullOrEmpty(e.Email)), () => { //Validation based on two fields in request model RuleFor(e => new {e.Username,e.Email }) .Must(x => !x.Email.Contains(x.Username)) .WithMessage(x=>$"Email should not contain the username: {x.Username}"); });
Validation based on service method using Dependency Injection**
Field: IdentificationNumber
Description: Here we validate IdentificationNumber matching certain criteria, we can write our own business logic in that method, and we can also using this method for any database related checks. We inject the service interface into the constructor of the validation class.
ValidationCode:1 2 3 4 5
RuleFor(e => e.IdentificationNumber) .NotEmpty() .WithMessage("Identification number required.") .MustAsync(async (f, \_) => await \_serviceMethods.ValidateIdentificationNumber(f)) .WithMessage("Identification number not valid");
Validation for each child List items**
Field: AddressList.PostBox
Description: Here we validate postbox field inside the list object AddressList. Each address object should have mandatory postbox text.
ValidationCode:1 2 3 4 5 6
RuleForEach(x => x.AddressList).ChildRules(items => { items.RuleFor(e => e.PostBox) .NotEmpty() .WithMessage("Postbox required."); });
Validation for List of Items using SetValidator**
Field: DocumentList
Description: Here we validate documentList using a separate validator method. We use this approach when documentList object is used in multiple places in the application, so all validation for this object remains in one place.
ValidationCode:1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
When(e => (e.DocumentList != null && e.DocumentList.Count > 0), () => { RuleForEach(x => x.DocumentList) .SetValidator(model => new DocumentValidator()); }); //DocumentValidator Class public class DocumentValidator : AbstractValidator<Document> { public DocumentValidator() { RuleFor(x => x.DocumentName) .NotEmpty() .WithMessage("Document name required"); RuleFor(x => x.CreatedDate) .LessThan(x => System.DateTime.Today) .WithMessage("Document created date cannot be greater than todays date."); RuleFor(x => x.ExpiryDate) .GreaterThan(x => System.DateTime.Today) .WithMessage("Document expiry date should be greater than todays date."); RuleFor(x => x.ExpiryDate) .GreaterThan(x => x.CreatedDate) .WithMessage("Document expiry date should be greater than created date."); } }
Validation based on the conditional rule in List of Items**
Field: DocumentList
Description: Here we validate items in documentList which are having IsActive value as true. This validation is closely similar to method 10 mentioned above, the only difference is that we need to add OverridePropertyName since there is a condition in the list of items.
ValidationCode:1 2 3 4 5 6
RuleForEach(model => model.DocumentList.Where(g => g.IsActive.HasValue && g.IsActive.Value)).ChildRules(items => { items.RuleFor(x => x.Id) .NotEmpty() .WithMessage("DocumentList Id required when document active."); }).OverridePropertyName("DocumentListValidatorWhenActive");
The complete source code of CustomerValidator and Document Validator is as below.
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public class CustomerValidator : AbstractValidator<Customer>
{
readonly List<string> genderTypes = EnumExtension.GetEnumValuesAndDescriptions<GenderTypes>().Select(c => c.Value).ToList();
public CustomerValidator(IServiceMethod \_serviceMethods)
{
//Validation for empty and null check for string field
RuleFor(x => x.FirstName)
.NotEmpty()
.WithMessage("First name required");
// Validation for nullable type
RuleFor(x => x.DateOfBirth)
.NotEmpty()
.WithMessage("Date of birth required");
//Validation based on When condition in a field
When(e => e.DateOfBirth.HasValue, () =>
{
RuleFor(model => model.DateOfBirth.Value.Date)
.LessThanOrEqualTo(x => System.DateTime.Today)
.WithMessage("Date of birth cannot be greater than todays date.");
//Validation using custom rule and Validation context
RuleFor(model => model.DateOfBirth.Value.Date)
.Custom((x, context) =>
{
if (x.AddYears(18) > DateTime.Now)
{
context.AddFailure($"Users with age less than 18 years not allowed to register, please check DateofBirth {x:dd-MMM-yyyy}");
}
});
});
// Validation for Email id using Regular Expression
RuleFor(x => x.Email)
.NotEmpty()
.WithMessage("Email required")
.Matches(@"^\[a-zA-Z0-9.!#$%&’\*+/=?^\_\`{|}~-\]+@\[a-zA-Z0-9-\]+(?:\\.\[a-zA-Z0-9-\]+)\*$")
.WithMessage("Email format is wrong.");
//Validation using a static method call
RuleFor(e => e.Mobile)
.NotEmpty()
.WithMessage("Mobile number required.")
.Must(x => Utility.ValidateMobileNumber(x))
.WithMessage("Mobile number Not Valid");
//Validation based on enum values with description, gender is optional value
When(e => !string.IsNullOrEmpty(e.Gender), () =>
{
RuleFor(e => e.Gender)
.Must(x => genderTypes.Contains(x.ToUpper()))
.WithMessage($"Gender is invalid, allowed values are {String.Join(",", genderTypes)}");
});
When(e => (!string.IsNullOrEmpty(e.Username) && !string.IsNullOrEmpty(e.Email)), () =>
{
//Validation based on two fields in request model
RuleFor(e => new {e.Username,e.Email })
.Must(x => !x.Email.Contains(x.Username))
.WithMessage(x=>$"Email should not contain the username: {x.Username}");
});
//Validation based on external service method
RuleFor(e => e.IdentificationNumber)
.NotEmpty()
.WithMessage("Identification number required.")
.MustAsync(async (f, \_) => await \_serviceMethods.ValidateIdentificationNumber(f))
.WithMessage("Identification number not valid");
//Validation for Child List items
RuleForEach(x => x.AddressList).ChildRules(items =>
{
items.RuleFor(e => e.PostBox)
.NotEmpty()
.WithMessage("Postbox required.");
});
//Validation with use of SetValidator seperate class
When(e => (e.DocumentList != null && e.DocumentList.Count > 0), () =>
{
RuleForEach(x => x.DocumentList)
.SetValidator(model => new DocumentValidator());
});
//Validation with conditional rule in a list of items
RuleForEach(model => model.DocumentList.Where(g => g.IsActive.HasValue
&& g.IsActive.Value)).ChildRules(items =>
{
items.RuleFor(x => x.Id)
.NotEmpty()
.WithMessage("DocumentList Id required when document active.");
}).OverridePropertyName("DocumentListValidatorWhenActive");
}
}
public class DocumentValidator : AbstractValidator<Document>
{
public DocumentValidator()
{
RuleFor(x => x.DocumentName)
.NotEmpty()
.WithMessage("Document name required");
RuleFor(x => x.CreatedDate)
.LessThan(x => System.DateTime.Today)
.WithMessage("Document created date cannot be greater than todays date.");
RuleFor(x => x.ExpiryDate)
.GreaterThan(x => System.DateTime.Today)
.WithMessage("Document expiry date should be greater than todays date.");
RuleFor(x => x.ExpiryDate)
.GreaterThan(x => x.CreatedDate)
.WithMessage("Document expiry date should be greater than created date.");
}
}
The full source code is in git FluentValidationDemo
Summary
We have seen twelve commonly needed use cases of Fluent validation in asp.net core. There are more use cases and scenarios for using this powerful library, you can visit the official documentation of Fluentvalidation for that docs.
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