How can I add a content type to an index programmatically?

Question

I'm trying to programmatically create indexes corresponding to several types, so I can search through items of specific types in my controllers. (I tried using the type keyword in Lucene, but that seems to not work at all no matter what I do, so I changed my approach.)

However, I can't figure out how to tell Orchard to include a specific type in an index in a migration. I tried using:

var typeIndexing = ContentDefinitionManager.GetTypeDefinition(contentType)
                .Settings.GetModel<TypeIndexing>();
typeIndexing.List = typeIndexing.List.Concat(indexName.Yield()).ToArray();

but that just returns null as the result of GetTypeDefinition().

I'm looking at using:

ContentDefinitionManager.AlterTypeDefinition(contentType, builder => {
    builder.WithSetting("TypeIndexing.Indexes", indexName);
});

but that seems like it replaces the previous configured index, if it works at all (EDIT: nope), and I don't want to clobber the existing setting. (A different person on the team is handling our setup recipe.)

Is there any place where I could touch that setting and have it be stored and actually used by Orchard outside the recipe file?

---

To illustrate what I'm trying to accomplish using the analogous admin UI changes, under Content Definition > [Content Type Name] > Edit:

Before:

After:

Answer 1

What you're looking for is the Indexed() extension method. It accepts the indexes you want to use on the content type.

ContentDefinitionManager.AlterTypeDefinition(nameof(contentType),type => 
type
.Indexed("FirstIndex", "SecondIndex"));