Making sure data is valid and business rules are kept

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Our Fitradar back-end solution is created based on Clean Architecture as described in this article and explained in this conference talk. One part of the back-end solution is incoming request validation, and in order to implement it as a part of the MediatR pipeline we are using FluentValidation library that replaces built-in ASP.NET Core validation system. At the beginning of the project it seemed that all we have to do is just to create a custom validator derived from AbstractValidator and perform the validation of an Application Model in a single class. And that is how we started to implement the validation. And since the library has quite enhanced capabilities that allow implementing complex validation rules for a while we didn’t notice any problems. Until the moment when we realized that not all validation rules are simple incoming Data Model validation. Some of the rules expressed our business logic rules and restrictions. And so we started to think about splitting the rules across the layers and following are multi step validation solution we came up with:

  • Application level validation. At this level incoming JSON data model fields validation is performed. The field types are validated automatically by ASP.NET core built-in Model binding but the other validation rules are executed by FluentValidation including:
    • required field validation
    • text field length validation
    • numeric field range validation
  • Domain level validation. At the domain level we apply Domain Driven Design approach and therefore instead of FluentValidation we decided to use Specification pattern. We liked the idea that we can move the validation logic outside the Domain Entity to the separate Validator. By doing that we were able to bind validation logic to incoming commands instead of Domain Entity. For example we have an entity SportEvent and several commands that call methods inside that entity like Update Sport Event and Cancel Sport Event. Now because the different commands have different business requirements for the same Entity property it would be hard to implement them with FluentValidation. For example property BookedSeats in case of Update Sport Event command should be 0, but in case of Cancel Sport Event command it is allowed that someone has already booked a particular Sport Event. And bellow is how the Cancel Sport Event validator looks like:
public sealed class EventCancellationValidator : EntityValidatorBase
    public EventCancellationValidator()
                new ValidationRule<SportEventInstance>(
                new Specification<SportEventInstance>(sportEvent =>
                    sportEvent.StartTime > DateTime.UtcNow),
                ValidationErrorCodes.CANCELLATION_TOO_LATE, "It is not possible to cancel the 
        Sport Event after it has started", "SportEventStartTime"));
  • Database level validation. For accessing database we are using Entity Framework Core and to make sure the database models are in tune with database constraints we are using built in property attributes and classes that implement IEntityTypeConfiguration interface that allows to define database constraints like Primary Key, Foreign Key and Unique Key.

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7 Benefits of Exercise

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  1. Help you control your weight.

Along with diet, exercise plays an important role in controlling your weight and preventing obesity. To maintain your weight, the calories you eat and drink must equal the energy you burn. To lose weight, you must use more calories than you eat and drink.

2. Reduce your risk of heart diseases.

Exercise strengthens your heart and improves your circulation. The increased blood flow raises the oxygen levels in your body. This helps lower your risk of heart diseases such as high cholesterol, coronary artery disease, and heart attack. Regular exercise can also lower your blood pressure and triglyceride levels.

3. Help your body manage blood sugar and insulin levels.

Exercise can lower your blood sugar level and help your insulin work better. This can cut down your risk for metabolic syndrome and type 2 diabetes. And if you already have one of those diseases, exercise can help you to manage it.

4. Improve your mental health and mood.

During exercise, your body releases chemicals that can improve your mood and make you feel more relaxed. This can help you deal with stress and reduce your risk of depression.

5. Strengthen your bones and muscles.

Regular exercise can help kids and teens build strong bones. Later in life, it can also slow the loss of bone density that comes with age. Doing muscle-strengthening activities can help you increase or maintain your muscle mass and strength.

6. Improve your sleep.

Exercise can help you to fall asleep faster and stay asleep longer.

7. Increase your chances of living longer.

Studies show that physical activity can reduce your risk of dying early from the leading causes of death, like heart disease and some cancers.

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P.S.S. Text from MedlinePlus

SwiftUI Tricks: Part 1

Photo by Clint Patterson on Unsplash

This is the first of mini articles in a series of SwiftUI tips and tricks.

One of the common tasks in mane applications is to determine screen width and layout items accordingly. FitRadar is not an exception. Many UI elements should be adjusted to screen size. There are two problems, tho: “screen” and “width”.


Most often developer’s think of a “view on screen” when saying “screen”. Physical screen size is equal to view controller size and vice versa. Yet we know that today (as per middle of 2021) we have iPad which allow run two apps side by side, or even one app in two “panels”. Know knows what else Apple introduce in future. We expect our fitness app to run on all possible devices: phones, tablets, watches, etc. So, we can’t rely on physical screen.


Since there is no yet (as per middle of 2021) devices with changing screen, most often developers think of a width of screen as a constant value. However, changing screen zoom (General -> Display & Brightness ->Display Zoom) actually change it. The other and most common scenario: rotation.

So, knowing these two problems we cannot rely anymore on something simple as



GeometryReader is second most advised way to get current view geometry. It does it best, but practise show that item places inside it acts differently on iOS 13 and iOS 14. And we actually want to avoid place our UI elements inside it.

For the trick we use PreferenceKey. Just add following code somewhere in project

struct SizePreferenceKey: PreferenceKey {   typealias Value = CGSize   static var defaultValue: Value = .zero   static func reduce(value: inout Value, nextValue: () -> Value) {    value = nextValue()   }}

Next, define some variable to keep current screen width

@State private var screenWidth: CGFloat = 0

Place geometry reader somewhere on the view which size you need to track. But other UI elements can now be placed outside GeometryReader

VStack {    GeometryReader { proxy in        Spacer()         .preference(key: SizePreferenceKey.self, value: proxy.size)    }    .frame(height: 1)    .onPreferenceChange(SizePreferenceKey.self) { preferences in        self.screenWidth = preferences.width    }    Rectangle()        .fill(        .frame(width: screenWidth / 2, height: screenWidth / 3)}

This solution works equally on iOS 13 and 14. Enjoy!

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