CleanArchitecture.Exceptions

A set of exceptions to be used in projects looking to follow clean architecture

Domain Layer Exceptions

In the domain layer object integrity is key, any domain rules of an object that are broken result in a DomainException. This forces the integrity of the entity make sure it's state is never not as expected. See below for the Parcel & ParcelItem entities that make use of this rule.

Parcel

public class Parcel
{
    private readonly List<ParcelItem> _items;
    
    public string Id { get; }

    public string Barcode { get; }

    public IReadOnlyList<ParcelItem> Items => _items;

    public Parcel(string barcode, List<ParcelItem> items)
    {
        if (string.IsNullOrWhiteSpace(barcode))
        {
            throw new DomainException<Parcel>("A parcel must have a barcode");
        }

        if (barcode.Length < 9)
        {
            throw new DomainException<Parcel>("A parcel's barcode must be at least 9 characters");
        }

        if (items.Count < 1)
        {
            throw new DomainException<Parcel>("A parcel must have at least one item");
        }
        
        Id = barcode;
        Barcode = barcode;
        _items = items;
    }
}

Parcel Item

public class ParcelItem
{
    public string Id { get; }
    
    public string ProductId { get; }

    public ParcelItem(string id, string productId)
    {
        if (string.IsNullOrWhiteSpace(id))
        {
            throw new DomainException<ParcelItem>("A parcel item must have an id");
        }
        
        if (string.IsNullOrWhiteSpace(productId))
        {
            throw new DomainException<ParcelItem>("A parcel item must have a product id");
        }
        
        Id = id;
        ProductId = productId;
    }
}

Application Layer Exceptions

Often when in the applicaiton layer of a project calls to some persitant data store is made and sometimes we don't have the record been requested or a record being created may conflict with one we aready have see the use of some of the common exceptions from this library below in the ParcelsService.

public class ParcelsService : IParcelsService
{
    private readonly IParcelRepository _parcelRepository;

    public ParcelsService(IParcelRepository parcelRepository)
    {
        _parcelRepository = parcelRepository;
    }
    
    public async ValueTask CreateParcel(CreateParcel newParcel)
    {
        if (await _parcelRepository.ParcelExists(newParcel.Barcode))
        {
            throw new ResourceExistsException<Parcel>($"A parcel with the barcode {newParcel.Barcode} already exists");
        }

        var parcelItems = newParcel.Items.Select(x => new ParcelItem(x.Id, x.ProductId)).ToList();
        var parcel = new Parcel(newParcel.Barcode, parcelItems);

        await _parcelRepository.CreateParcel(parcel);
    }

    public async ValueTask<ParcelDto> GetParcel(string barcode)
    {
        Parcel? parcel = await _parcelRepository.GetParcel(barcode);

        if (parcel is null)
        {
            throw new ResourceNotFoundException<Parcel>($"A parcel with the barcode {barcode} does not exist");
        }

        return new ParcelDto()
        {
            Barcode = parcel.Barcode,
            Items = parcel.Items.Select(x => new ParcelItemDto(x.Id, x.ProductId))
        };
    }

    public async ValueTask<ParcelItem> GetParcelItem(string parcelItemId)
    {
        ParcelItem? parcelItem = await _parcelRepository.GetParcelItem(parcelItemId);

        if (parcelItem is null)
        {
            throw new ResourceNotFoundException<Parcel>($"A parcel item with the id {parcelItemId} does not exist");
        }

        return new ParcelItem(parcelItem.Id, parcelItem.ProductId);
    }
}

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