Register an EventProjection's published types as teardown targets (#626)

src/EventTests/Projections/EventProjectionTests.cs

@@ -112,4 +112,121 @@ protected override void storeEntity<T>(FakeOperations ops, T entity)
     {
         throw new NotImplementedException();
     }
-}
+}
+/// <summary>
+/// jasperfx#626 — JasperFxEventProjectionBase's constructor never touched Options, so an
+/// EventProjection registered NO teardown targets: a rebuild deleted the progression row and then
+/// re-projected into a table still holding the previous run's documents, and the ProjectionScenario
+/// harness wipe (which reads Options.StorageTypes) did nothing after an event projection. Aggregation
+/// projections have always registered their single TDoc; nothing in the API surface signalled the
+/// difference, so every event projection author had to know it independently.
+/// </summary>
+public class EventProjectionTeardownTests
+{
+    private static Type[] cleanupTypes(ProjectionBase projection)
+        => projection.Options.CleanUps.OfType<DeleteDocuments>().Select(x => x.DocumentType).ToArray();
+
+    [Fact]
+    public void published_types_become_teardown_targets()
+    {
+        var projection = new CreatesDocumentsProjection();
+
+        // Nothing is registered until assembly -- the source generator emits its
+        // RegisterPublishedType calls into the subclass constructor, after the base one
+        projection.Options.CleanUps.ShouldBeEmpty();
+
+        projection.AssembleAndAssertValidity();
+
+        cleanupTypes(projection).ShouldBe([typeof(DocOne)]);
+        projection.Options.StorageTypes.ShouldContain(typeof(DocOne));
+    }
+
+    [Fact]
+    public void every_published_type_is_registered_not_just_the_first()
+    {
+        var projection = new CreatesTwoDocumentsProjection();
+        projection.AssembleAndAssertValidity();
+
+        cleanupTypes(projection).ShouldBe([typeof(DocOne), typeof(DocTwo)], ignoreOrder: true);
+    }
+
+    [Fact]
+    public void a_projection_that_publishes_nothing_registers_nothing()
+    {
+        var projection = new ConventionalEventProjection();
+        projection.AssembleAndAssertValidity();
+
+        projection.Options.CleanUps.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void the_opt_out_wins_over_the_default()
+    {
+        // For a projection writing into storage that must not be truncated on rebuild
+        var projection = new AppendOnlyProjection();
+        projection.AssembleAndAssertValidity();
+
+        projection.Options.CleanUps.ShouldBeEmpty();
+        projection.Options.StorageTypes.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void a_hand_registered_type_is_not_duplicated()
+    {
+        var projection = new CreatesDocumentsProjection();
+        projection.Options.DeleteViewTypeOnTeardown<DocOne>();
+
+        projection.AssembleAndAssertValidity();
+
+        cleanupTypes(projection).ShouldBe([typeof(DocOne)]);
+    }
+
+    [Fact]
+    public void assembling_twice_does_not_duplicate_the_registrations()
+    {
+        // ProjectionGraph assembles on more than one path; a second pass must be a no-op
+        var projection = new CreatesDocumentsProjection();
+        projection.AssembleAndAssertValidity();
+        projection.AssembleAndAssertValidity();
+
+        cleanupTypes(projection).ShouldBe([typeof(DocOne)]);
+    }
+
+    [Fact]
+    public void an_explicitly_registered_type_survives_the_opt_out()
+    {
+        // The documented "some but not all" recipe: opt out, then declare what you do want wiped
+        var projection = new AppendOnlyProjection();
+        projection.Options.DeleteViewTypeOnTeardown<DocTwo>();
+
+        projection.AssembleAndAssertValidity();
+
+        cleanupTypes(projection).ShouldBe([typeof(DocTwo)]);
+    }
+}
+
+public class DocOne;
+
+public class DocTwo;
+
+public partial class CreatesDocumentsProjection : EventProjection
+{
+    public DocOne Create(AEvent e) => new();
+}
+
+public partial class CreatesTwoDocumentsProjection : EventProjection
+{
+    public DocOne Create(AEvent e) => new();
+
+    public DocTwo Create(BEvent e) => new();
+}
+
+public partial class AppendOnlyProjection : EventProjection
+{
+    public AppendOnlyProjection()
+    {
+        DeletePublishedTypesOnTeardown = false;
+    }
+
+    public DocOne Create(AEvent e) => new();
+}

src/JasperFx.Events/Projections/JasperFxEventProjectionBase.cs

@@ -150,8 +150,45 @@ void IEntityStorage<TOperations>.Store<T>(TOperations ops, T entity)
 
     protected abstract void storeEntity<T>(TOperations ops, T entity) where T : notnull;
 
+    /// <summary>
+    /// jasperfx#626: whether the document types this projection publishes are automatically
+    /// registered as teardown targets (<see cref="AsyncOptions.DeleteViewTypeOnTeardown(Type)" />),
+    /// so a rebuild wipes the previous run's documents before re-projecting. True by default, which
+    /// matches what aggregation projections have always done for their single view type.
+    ///
+    /// <para>
+    /// Set to false when this projection writes into storage that must NOT be truncated on rebuild —
+    /// an append-only audit table, or documents another projection owns. With it off, nothing is
+    /// registered automatically and <see cref="ProjectionBase.Options" />'s teardown rules are
+    /// entirely yours to declare. It is all-or-nothing: to keep automatic registration for some
+    /// published types only, turn it off and call <c>Options.DeleteViewTypeOnTeardown&lt;T&gt;()</c>
+    /// for the ones you do want wiped.
+    /// </para>
+    /// </summary>
+    public bool DeletePublishedTypesOnTeardown { get; set; } = true;
+
+    // jasperfx#626: an EventProjection can publish several document types, so the base constructor
+    // cannot do what JasperFxAggregationProjectionBase does with its single TDoc -- and it could not
+    // do it there anyway, because the source generator emits its RegisterPublishedType calls into the
+    // subclass constructor, which runs AFTER this base one. Deferring to AssembleAndAssertValidity
+    // (registration time, via ProjectionGraph) sees the complete set and lets a subclass constructor
+    // turn the behavior off before it happens. Idempotent: a type the author already registered by
+    // hand, or a previous pass, is skipped rather than duplicated.
+    private void registerPublishedTypesForTeardown()
+    {
+        if (!DeletePublishedTypesOnTeardown) return;
+
+        foreach (var publishedType in PublishedTypes().ToArray())
+        {
+            if (Options.StorageTypes.Contains(publishedType)) continue;
+            Options.DeleteViewTypeOnTeardown(publishedType);
+        }
+    }
+
     public sealed override void AssembleAndAssertValidity()
     {
+        registerPublishedTypesForTeardown();
+
         var applyMethod = GetType()!.GetMethod(nameof(ApplyAsync))!;
         var isOverridden = applyMethod.DeclaringType!.Assembly != typeof(JasperFxEventProjectionBase<,>).Assembly;
         if (isOverridden)