Preventing Autofixture from filling child collections

Question

I'm using the latest version of Autofixture, and I'd like to prevent it from filling automatically child collections.

For example, I have a class Person that has a List property. I want all properties filled, except the list.

I tried using this customization :

public class RemoveMultiples : ICustomization
{
    public void Customize(IFixture fixture)
    {
        fixture.Customizations
            .OfType<FilteringSpecimenBuilder>()
            .Where(x => x.Specification is DictionarySpecification)
            .ToList().ForEach(c => fixture.Customizations.Remove(c));
        fixture.Customizations
            .OfType<FilteringSpecimenBuilder>()
            .Where(x => x.Specification is CollectionSpecification)
            .ToList().ForEach(c => fixture.Customizations.Remove(c));
        fixture.Customizations
            .OfType<FilteringSpecimenBuilder>()
            .Where(x => x.Specification is HashSetSpecification)
            .ToList().ForEach(c => fixture.Customizations.Remove(c));
        fixture.Customizations
            .OfType<FilteringSpecimenBuilder>()
            .Where(x => x.Specification is ListSpecification)
            .ToList().ForEach(c => fixture.Customizations.Remove(c));
    }
}

But it also prevents me from using .CreateMany().

edit: I can use .CreateMany(3) and it works.

Is there a setting somewhere that could let me autofill collections only when I need to?

edit2: Class person should look like this:

[Serializable]
public class Person
{
    private ICollection<OtherClass> _otherClasses; 
    private string _something;
    public virtual ICollection<OtherClass> OtherClasses
    {
        get { return _otherClasses; }
        set { _otherClasses = value; }
    }
}

Note that it's not always a Collection, but sometimes IList

Note2: I just realized that someone also removed the Customization for IEnumerable hence why the CreateMany() doesn't create anything.

Answer 1

Here's one way to do it.

Start by implementing a SpecimenBuilder that tells AutoFixture to skip assigning a value for collection property:

public class CollectionPropertyOmitter : ISpecimenBuilder
{
    public object Create(object request, ISpecimenContext context)
    {
        var pi = request as PropertyInfo;
        if (pi != null
            && pi.PropertyType.IsGenericType
            && pi.PropertyType.GetGenericTypeDefinition() == typeof(ICollection<>))
            return new OmitSpecimen();

        return new NoSpecimen(request);
    }
}

Then encapsulate that in a Customization:

public class DoNotFillCollectionProperties : ICustomization
{
    public void Customize(IFixture fixture)
    {
        fixture.Customizations.Add(new CollectionPropertyOmitter());
    }
}

The following tests now pass:

[Fact]
public void CreatePersonWithoutFillingCollectionProperty()
{
    var fixture = new Fixture().Customize(new DoNotFillCollectionProperties());
    var actual = fixture.Create<Person>();
    Assert.Null(actual.OtherClasses);
}

[Fact]
public void CreateManyStillWorks()
{
    var fixture = new Fixture().Customize(new DoNotFillCollectionProperties());
    var actual = fixture.CreateMany<Person>();
    Assert.NotEmpty(actual);
}

[Fact]
public void CreatListStillWorks()
{
    var fixture = new Fixture().Customize(new DoNotFillCollectionProperties());
    var actual = fixture.Create<List<Person>>();
    Assert.NotEmpty(actual);
}

[Fact]
public void CreateCollectionStillWorks()
{
    var fixture = new Fixture().Customize(new DoNotFillCollectionProperties());
    var actual = fixture.Create<ICollection<Person>>();
    Assert.NotEmpty(actual);
}