What is the process for validating and formatting start_date and end_date using fluent validator in ASP.NET Core Web API?

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Here's a sample implementation of validation and formatting for startdate and enddate using fluent validator in ASP.NET Core Web API:

1. Install FluentValidation.AspNetCore package via NuGet:

Install-Package FluentValidation.AspNetCore

1. Create a custom model class that includes the startdate and enddate properties:

public class DateRangeModel {
    public DateTime start_date { get; set; }
    public DateTime end_date { get; set; }
}

1. Create a custom validator class that inherits from AbstractValidator<daterangemodel>:

public class DateRangeModelValidator : AbstractValidator<DateRangeModel> {
    public DateRangeModelValidator() {
        RuleFor(x => x.start_date)
            .NotEmpty().WithMessage("Start date is required.")
            .LessThan(x => x.end_date).WithMessage("Start date cannot be after end date.")
            .Must(x => x > DateTime.MinValue).WithMessage("Invalid start date format.");

        RuleFor(x => x.end_date)
            .NotEmpty().WithMessage("End date is required.")
            .GreaterThan(x => x.start_date).WithMessage("End date cannot be before start date.")
            .Must(x => x > DateTime.MinValue).WithMessage("Invalid end date format.");
    }
}

1. In your controller, add the [ValidatorActionFilter] attribute to automatically validate the model before passing it to the action:

[HttpPost]
[ValidatorActionFilter]
public IActionResult Post(DateRangeModel model) {
    // Do something with the validated model
    return Ok();
}

1. To format the startdate and enddate properties, you can add a custom date converter to the Json output formatter in Startup.cs:

services.AddMvc()
    .AddFluentValidation()
    .AddJsonOptions(options => {
        options.SerializerSettings.Converters.Add(new IsoDateTimeConverter {
            DateTimeStyles = DateTimeStyles.AssumeUniversal,
            DateTimeFormat = "yyyy-MM-ddTHH:mm:ssZ"
        });
    });

This will format the dates in ISO 8601 format with UTC offset, which is widely supported by various systems and applications.