Deleting Facts

Facts are not truly deleted. You indicate that they should be deleted by introducing a new fact. There are mechanisms for taking them out of storage, but we'll cover those later.

To indicate that a site should be deleted, define a fact that refers to the site as a predecessor. It also should have a timestamp so that we can differentiate one deletion from another.

[FactType("Blog.Site.Deleted")]
public record SiteDeleted(Site site, DateTime deletedAt) { }

Renderer.RenderTypes(typeof(SiteDeleted))

To indicate that a site should be deleted, create an instance of that fact.

var siteDeleted = await jinagaClient.Fact(new SiteDeleted(site, DateTime.UtcNow));

jinagaClient.RenderFacts(siteDeleted)

If you query the specification now, you will still see the site.

sites = await jinagaClient.Query(sitesByUser, user);

sites.Count()

1

That's because we need to change the specification to exclude deleted sites. Add a clause that filters out sites that have a site deleted successor.

sitesByUser = Given<User>.Match((user, facts) =>
    from site in facts.OfType<Site>()
    where site.creator == user
    // Include only the sites that have not been deleted
    where !facts.Any<SiteDeleted>(sd => sd.site == site)
    select site);

sites = await jinagaClient.Query(sitesByUser, user);

sites.Count()

0