In DDD where to keep custom exceptions (application exceptions)? In Infrastructure layer?

Question

I'm building a app with following architecture:

UI - Application - Domain - Infrastructure

I have a Application Layer that need use custom exceptions. Where I keep these custom exceptions? In Infrastructure layer? The problem is my Application Layer don't have reference to Infrastructure layer.

What is the correct way?

Update:

Here's my code that throw a exception in Application Layer:

public void InsertNewImage(ImagemDTO imagemDTO)
{
    if (isValidContentType(imagemDTO.ImageStreamContentType))
    {
        string nameOfFile = String.Format("{0}{1}", Guid.NewGuid().ToString(), ContentTypeHelper.GetExtension(imagemDTO.ImageStreamContentType));

        string path = String.Format("{0}{1}", ImageSettings.PathToSave, nameOfFile);

        _fileService.SaveFile(imagemDTO.ImageStream, path);

        Imagem imagem = new Imagem()
                            {
                                Titulo = imagemDTO.Titulo,
                                Descricao = imagemDTO.Descricao,
                                NomeArquivo = nameOfFile
                            };

        _imagemRepository.Add(imagem);

        _dbContext.SaveChanges();
    } else
    {
        throw new WrongFileTypeException(String.Format("{0} is not allowed.", ContentTypeHelper.GetExtension(imagemDTO.ImageStreamContentType)));
    }
}

Even ImageSettings is a ConfigurationSection is in my Application Layer because it uses it. I don't see other way I can transfer my ImageSettings (which should stay in Infrastrucuture Layer) to Infrastructure Layer, someone can help?

public class ImageSettings : ConfigurationSection
{
    /// <summary>
    /// Caminha onde será salvo as imagens
    /// </summary>
    [ConfigurationProperty("pathToSave", IsRequired = true)]
    public string PathToSave
    {
        get { return (string)this["pathToSave"]; }
        set { this["pathToSave"] = value; }
    }

    /// <summary>
    /// Extensões permitidas pra upload
    /// </summary>
    [ConfigurationProperty("allowedExtensions", IsRequired = true)]
    public string AllowedExtensions
    {
        get { return (string)this["allowedExtensions"]; }
        set { this["allowedExtensions"] = value; }
    }

    /// <summary>
    /// Tamanho das imagens
    /// </summary>
    [ConfigurationProperty("imageSize")]
    public ImageSizeCollection ImageSize
    {
        get
        {
            return (ImageSizeCollection)this["imageSize"];
        }
    }
}

Answer 1

In DDD where to keep custom exceptions (application exceptions)? In Infrastructure layer?

• No

Why?

• In a Clean Architecture, a center layer never depends on the outside, always the inverse
• "The fundamental rule is that all code can depend on layers more central, but code cannot depend on layers further out from the core. In other words, all coupling is toward the center.". Please check the article from Jeffrey Palermo.

I've written an article with Onion Architecture with a code sample. Please check this.

But basically, you should add your custom exception to your layer (Application in this case). Just create a folder "Exceptions" and then add your user-defined exception there. Please check this link for my details about how to create user-defined exceptions