A Word On Factory Results and Contracts


Filed under: Vigil Journey

For simplicity, the PatronFactory's CreatePatron method just returned an IKeyIdentity. This was a simple interface that requires an Id of type Guid. When the creation method was always assumed to work correctly, this was fine - I don't have to worry about validation checking, data errors, or anything that might cause a failure. However, in the real world, I need to be aware of these things. As such, the first refactor that I'm going to perform is to change the return type to a multi-purpose class.


using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

namespace Vigil.Domain
    public class FactoryResult
        public ICollection<ValidationResult> ValidationResults { get; protected set; }
        public IKeyIdentity AffectedEntity { get; protected set; }

        public FactoryResult(ICollection<ValidationResult> validationResults)
            ValidationResults = validationResults;
        public FactoryResult(IKeyIdentity affectedEntity)
            AffectedEntity = affectedEntity;

The PatronFactory will now return this class. If there were problems, then the ValidationResults collection will contain elements; if all went well, then IKeyIdentity should not be null. Tests were updated to reflect this, and now I am ready to add validation (next post).

A Quick Note About Contracts

Currently, Code Contracts is not supported for .NetCore and is not coming to C# 7.0, which makes me very sad - it is also the number one requested feature for C# on the Visual Studio uservoice. While the primary use of Design by Contract was for eliminating null references, there were still plenty of other places it was extremely useful. Especially with Guids becoming the primary source of identifiers, it was very helpful to be able to Require that a Guid could not be Empty, or that a value was in a given range.

So, it is with a sad heart that I have removed Contracts from this project entirely. I will start putting in null reference checks where appropriate, but for the most part, I will do what I can to find an alternative solution.