How to valid DateofBirth using fluent Validation in C# if it exceeds current year?

FluentValidation in C# provides a powerful way to validate model properties using a fluent interface. When validating date of birth, you need to ensure the date doesn't exceed the current year and falls within a reasonable age range.

This validation is essential for preventing future dates in birth date fields and ensuring data integrity in applications dealing with user registration or profile management.

Syntax

Following is the syntax for creating a date of birth validation rule using FluentValidation −

RuleFor(p => p.DateOfBirth)
    .Must(BeAValidAge)
    .WithMessage("Invalid {PropertyName}");

Following is the syntax for running the validator −

ValidationResult results = validator.Validate(person);

Key Components

• RuleFor − Specifies which property to validate using a lambda expression.

• Must − Defines a custom validation condition that must return true.

• WithMessage − Specifies the error message when validation fails.

• ValidationResult − Contains validation results with IsValid boolean and Errors collection.

Using Custom Validation Method

The following example demonstrates how to validate date of birth to ensure it doesn't exceed the current year and falls within a reasonable age range −

using System;
using System.Collections.Generic;
using FluentValidation;
using FluentValidation.Results;

public class PersonModel {
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public decimal AccountBalance { get; set; }
    public DateTime DateOfBirth { get; set; }
}

public class PersonValidator : AbstractValidator<PersonModel> {
    public PersonValidator() {
        RuleFor(p => p.DateOfBirth)
            .Must(BeAValidAge).WithMessage("Invalid {PropertyName}");
    }

    protected bool BeAValidAge(DateTime date) {
        int currentYear = DateTime.Now.Year;
        int dobYear = date.Year;

        if (dobYear <= currentYear && dobYear > (currentYear - 120)) {
            return true;
        }

        return false;
    }
}

class Program {
    static void Main(string[] args) {
        List<string> errors = new List<string>();

        PersonModel person = new PersonModel();
        person.FirstName = "TestUser";
        person.LastName = "TestUser";
        person.AccountBalance = 100;
        person.DateOfBirth = DateTime.Now.Date.AddYears(1);

        PersonValidator validator = new PersonValidator();
        ValidationResult results = validator.Validate(person);

        if (results.IsValid == false) {
            foreach (ValidationFailure failure in results.Errors) {
                errors.Add(failure.ErrorMessage);
            }
        }

        foreach (var item in errors) {
            Console.WriteLine(item);
        }
    }
}

The output of the above code is −

Invalid Date Of Birth

Using Built-in Date Range Validation

FluentValidation also provides built-in methods for date range validation −

using System;
using System.Collections.Generic;
using FluentValidation;
using FluentValidation.Results;

public class PersonModel {
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public DateTime DateOfBirth { get; set; }
}

public class PersonValidator : AbstractValidator<PersonModel> {
    public PersonValidator() {
        RuleFor(p => p.DateOfBirth)
            .LessThan(DateTime.Today)
            .WithMessage("Date of birth cannot be in the future")
            .GreaterThan(DateTime.Today.AddYears(-120))
            .WithMessage("Date of birth cannot be more than 120 years ago");
    }
}

class Program {
    static void Main(string[] args) {
        PersonModel person = new PersonModel {
            FirstName = "John",
            LastName = "Doe",
            DateOfBirth = DateTime.Today.AddDays(10)
        };

        PersonValidator validator = new PersonValidator();
        ValidationResult results = validator.Validate(person);

        if (!results.IsValid) {
            foreach (var error in results.Errors) {
                Console.WriteLine(error.ErrorMessage);
            }
        } else {
            Console.WriteLine("Validation passed!");
        }
    }
}

The output of the above code is −

Date of birth cannot be in the future

Validation Result Properties

Conclusion

FluentValidation provides flexible options for validating date of birth fields in C#. You can use custom validation methods with Must() or built-in methods like LessThan() and GreaterThan() to ensure dates don't exceed the current year and fall within acceptable ranges.