Can I replace FactoryMethodQuery for all types

[grzesiek-galezowski]

Hi,

The current version of FactoryMethodQuery uses factory methods with fewest parameters. Unfortunately, this doesn't work for me as in many cases, I have static properties like Empty that return "null objects" and they get called which is usually not what I want.

Can I somehow configure AutoFixture to replace or remove the query?

[zvirja]

Hello,

The part in the question belongs to the Engine, passed to the Fixture constructor. You can replace it if you pass the customized engine. See the full demo below (hope I correctly got your question):

public class UnitTest1
{
    [Fact]
    public void CustomizedEngineDemo()
    {
        var fixture = new Fixture(new EngineWithReplacedQuery());

        var result = fixture.Create<TypeWithNullObject>();

        Assert.NotSame(TypeWithNullObject.Empty, result);
    }

    public class EngineWithReplacedQuery : DefaultEngineParts
    {
        public override IEnumerator<ISpecimenBuilder> GetEnumerator()
        {
            using (var enumerator = base.GetEnumerator())
            {
                while (enumerator.MoveNext())
                {
                    var value = enumerator.Current;

                    // Replace target method query
                    if (value is MethodInvoker mi &&
                        mi.Query is CompositeMethodQuery cmq &&
                        cmq.Queries.Skip(1).FirstOrDefault() is FactoryMethodQuery)
                    {
                        yield return new MethodInvoker(
                            new CompositeMethodQuery(
                                new ModestConstructorQuery(),
                                new PatchedFactoryMethodQuery()
                            )
                        );
                    }
                    else
                    {
                        yield return value;
                    }
                }
            }
        }
    }

    public class PatchedFactoryMethodQuery : IMethodQuery
    {
        public IEnumerable<IMethod> SelectMethods(Type type)
        {
            return from mi in type.GetTypeInfo().GetMethods(BindingFlags.Static | BindingFlags.Public)
                where mi.ReturnType == type &&
                      !string.Equals(mi.Name, "op_Implicit", StringComparison.Ordinal) &&
                      !string.Equals(mi.Name, "op_Explicit", StringComparison.Ordinal) 
                let parameters = mi.GetParameters()
                where mi.GetParameters().All(p => p.ParameterType != type)
                orderby mi.GetCustomAttribute<CompilerGeneratedAttribute>() == null ? 0 : 1, parameters.Length ascending
                select new StaticMethod(mi) as IMethod;
        }
    }


    public class TypeWithNullObject
    {
        public string Value { get; }

        private TypeWithNullObject(string value)
        {
            Value = value;
        }

        public static TypeWithNullObject Empty { get; } = new TypeWithNullObject("<empty>");

        public static TypeWithNullObject CreateValue(string value) => new TypeWithNullObject(value);
    }
}

Let me know whether it solves your issue.

P.S. I've registered a wish #1018 to simplify the default builders customization.

[grzesiek-galezowski]

Thank you for your extensive help, this allowed me to solve the issue I had. Thumbs up for making this easier!