[C#] Primary keys for query builder views (#4626)

# Description of Changes

Same change set as
#4614, just targeting
master.

The return type of a query builder view is now a special SATS product
type `{ __query__: T }`. A view with this return type now has a primary
key if `T` has a primary key. This means that client codegen will
generate an `OnUpdate` callback for such views. It will also generate
query builder index bindings for the primary key column.

# API and ABI breaking changes

None. Old modules with query builder views still work, they just don't
have primary keys.

# Expected complexity level and risk

2

# Testing

Added equivalent tests to the ones that were added in #4573 and #4572.

Author: joshua-spacetime

crates/bindings-csharp/BSATN.Runtime/BSATN/AlgebraicType.cs

@@ -39,6 +39,7 @@ Unit F64
     )>
 {
     public static readonly AlgebraicType Unit = new Product([]);
+    public const string QueryBuilderProductTypeTag = "__query__";
 
     // Special AlgebraicType that can be recognised by the SpacetimeDB `generate` CLI as an Option<T>.
     internal static AlgebraicType MakeOption(AlgebraicType someType) =>
@@ -47,4 +48,8 @@ internal static AlgebraicType MakeOption(AlgebraicType someType) =>
     // Special AlgebraicType that can be recognised by the SpacetimeDB `generate` CLI as a Result<T, E>.
     internal static AlgebraicType MakeResult(AlgebraicType okType, AlgebraicType errType) =>
         new Sum([new("ok", okType), new("err", errType)]);
+
+    // Special AlgebraicType that can be recognised by the SpacetimeDB `generate` CLI as Query<T>.
+    public static AlgebraicType MakeQueryBuilderProductType(Ref rowProductTypeRef) =>
+        new Product([new(QueryBuilderProductTypeTag, rowProductTypeRef)]);
 }

crates/bindings-csharp/Codegen.Tests/fixtures/server/snapshots/Module#FFI.verified.cs

@@ -1636,10 +1636,9 @@ SpacetimeDB.BSATN.ITypeRegistrar registrar
             IsPublic: true,
             IsAnonymous: false,
             Params: [],
-            ReturnType: new SpacetimeDB.BSATN.ValueOption<
-                PublicTable,
-                PublicTable.BSATN
-            >().GetAlgebraicType(registrar)
+            ReturnType: global::SpacetimeDB.BSATN.AlgebraicType.MakeQueryBuilderProductType(
+                new PublicTable.BSATN().GetAlgebraicType(registrar)
+            )
         );
 
     public byte[] Invoke(

crates/bindings-csharp/Codegen/Module.cs

@@ -1122,6 +1122,7 @@ record ViewDeclaration
     public readonly bool IsPublic;
     public readonly bool ReturnsQuery;
     public readonly TypeUse ReturnType;
+    public readonly TypeUse? QueryRowType;
     public readonly EquatableArray<MemberDeclaration> Parameters;
     public readonly Scope Scope;
 
@@ -1186,15 +1187,12 @@ method.ReturnType is INamedTypeSymbol
         {
             ReturnsQuery = true;
             var rowType = TypeUse.Parse(method, queryRowType, diag);
-            var optType = queryRowType.IsValueType
-                ? "SpacetimeDB.BSATN.ValueOption"
-                : "SpacetimeDB.BSATN.RefOption";
-            var opt = $"{optType}<{rowType.Name}, {rowType.BSATNName}>";
-            // Match Rust semantics: Query<T> is described as a nullable row (T?).
-            ReturnType = new ReferenceUse(opt, opt);
+            QueryRowType = rowType;
+            ReturnType = rowType;
         }
         else
         {
+            QueryRowType = null;
             ReturnType = TypeUse.Parse(method, method.ReturnType, diag);
         }
         Scope = new Scope(methodSyntax.Parent as MemberDeclarationSyntax);
@@ -1211,9 +1209,10 @@ method.ReturnType is INamedTypeSymbol
             diag.Report(ErrorDescriptor.ViewContextParam, methodSyntax);
         }
 
-        // Validate return type: must be List<T> or T?
+        // Validate return type: must be List<T>, T?, or IQuery<T>.
         if (
-            !ReturnType.BSATNName.Contains("SpacetimeDB.BSATN.ValueOption")
+            !ReturnsQuery
+            && !ReturnType.BSATNName.Contains("SpacetimeDB.BSATN.ValueOption")
             && !ReturnType.BSATNName.Contains("SpacetimeDB.BSATN.RefOption")
             && !ReturnType.BSATNName.Contains("SpacetimeDB.BSATN.List")
         )
@@ -1229,17 +1228,22 @@ method.ReturnType is INamedTypeSymbol
         );
     }
 
-    public string GenerateViewDef(uint Index) =>
-        $$$"""
+    public string GenerateViewDef(uint Index)
+    {
+        var returnTypeExpr = ReturnsQuery
+            ? $"global::SpacetimeDB.BSATN.AlgebraicType.MakeQueryBuilderProductType(new {QueryRowType!.BSATNName}().GetAlgebraicType(registrar))"
+            : $"new {ReturnType.BSATNName}().GetAlgebraicType(registrar)";
+        return $$$"""
             new global::SpacetimeDB.Internal.RawViewDefV10(
                 SourceName: "{{{Name}}}",
                 Index: {{{Index}}},
                 IsPublic: {{{IsPublic.ToString().ToLower()}}},
                 IsAnonymous: {{{IsAnonymous.ToString().ToLower()}}},
                 Params: [{{{MemberDeclaration.GenerateDefs(Parameters)}}}],
-                ReturnType: new {{{ReturnType.BSATNName}}}().GetAlgebraicType(registrar)
+                ReturnType: {{{returnTypeExpr}}}
             );
             """;
+    }
 
     /// <summary>
     /// Generates the class responsible for evaluating a view.

crates/codegen/src/csharp.rs

@@ -653,6 +653,13 @@ impl Lang for Csharp<'_> {
                 }
             }
         }
+        for (columns, constraints) in schema.backcompat_column_constraints() {
+            if constraints.has_indexed() || constraints.has_unique() || constraints.has_primary_key() {
+                for col_pos in columns.iter() {
+                    ix_col_positions.insert(col_pos.idx());
+                }
+            }
+        }
 
         writeln!(output, "public sealed class {cols_owner_name}Cols");
         indented_block(&mut output, |output| {

modules/sdk-test-view-pk-cs/.gitignore

@@ -0,0 +1,2 @@
+bin
+obj

modules/sdk-test-view-pk-cs/Lib.cs

@@ -0,0 +1,92 @@
+namespace SpacetimeDB.Sdk.Test.ViewPk;
+
+using SpacetimeDB;
+
+public static partial class Module
+{
+    [SpacetimeDB.Table(Accessor = "view_pk_player", Public = true)]
+    public partial struct ViewPkPlayer
+    {
+        [SpacetimeDB.PrimaryKey]
+        public ulong id;
+        public string name;
+    }
+
+    [SpacetimeDB.Table(Accessor = "view_pk_membership", Public = true)]
+    public partial struct ViewPkMembership
+    {
+        [SpacetimeDB.PrimaryKey]
+        public ulong id;
+
+        [SpacetimeDB.Index.BTree]
+        public ulong player_id;
+    }
+
+    [SpacetimeDB.Table(Accessor = "view_pk_membership_secondary", Public = true)]
+    public partial struct ViewPkMembershipSecondary
+    {
+        [SpacetimeDB.PrimaryKey]
+        public ulong id;
+
+        [SpacetimeDB.Index.BTree]
+        public ulong player_id;
+    }
+
+    [SpacetimeDB.Reducer]
+    public static void insert_view_pk_player(ReducerContext ctx, ulong id, string name)
+    {
+        ctx.Db.view_pk_player.Insert(new ViewPkPlayer { id = id, name = name });
+    }
+
+    [SpacetimeDB.Reducer]
+    public static void update_view_pk_player(ReducerContext ctx, ulong id, string name)
+    {
+        ctx.Db.view_pk_player.id.Update(new ViewPkPlayer { id = id, name = name });
+    }
+
+    [SpacetimeDB.Reducer]
+    public static void insert_view_pk_membership(ReducerContext ctx, ulong id, ulong player_id)
+    {
+        ctx.Db.view_pk_membership.Insert(new ViewPkMembership { id = id, player_id = player_id });
+    }
+
+    [SpacetimeDB.Reducer]
+    public static void insert_view_pk_membership_secondary(
+        ReducerContext ctx,
+        ulong id,
+        ulong player_id
+    )
+    {
+        ctx.Db.view_pk_membership_secondary.Insert(
+            new ViewPkMembershipSecondary { id = id, player_id = player_id }
+        );
+    }
+
+    [SpacetimeDB.View(Accessor = "all_view_pk_players", Public = true)]
+    public static IQuery<ViewPkPlayer> all_view_pk_players(ViewContext ctx)
+    {
+        return ctx.From.view_pk_player();
+    }
+
+    [SpacetimeDB.View(Accessor = "sender_view_pk_players_a", Public = true)]
+    public static IQuery<ViewPkPlayer> sender_view_pk_players_a(ViewContext ctx)
+    {
+        return ctx
+            .From.view_pk_membership()
+            .RightSemijoin(
+                ctx.From.view_pk_player(),
+                (membership, player) => membership.player_id.Eq(player.id)
+            );
+    }
+
+    [SpacetimeDB.View(Accessor = "sender_view_pk_players_b", Public = true)]
+    public static IQuery<ViewPkPlayer> sender_view_pk_players_b(ViewContext ctx)
+    {
+        return ctx
+            .From.view_pk_membership_secondary()
+            .RightSemijoin(
+                ctx.From.view_pk_player(),
+                (membership, player) => membership.player_id.Eq(player.id)
+            );
+    }
+}

modules/sdk-test-view-pk-cs/README.md

@@ -0,0 +1,8 @@
+# `sdk-test-view-pk-cs` *C#* test
+
+See the [sdk-test-view-pk README](../sdk-test-view-pk/README.md) for more details.
+
+> **WARNING**: This C# source code is manually derived from `../sdk-test-view-pk/src/lib.rs`
+> and is supposed to be functionally equivalent.
+> Do not add new types or functionality here that are not present in the *Rust* version,
+> because they're compared against each other.

modules/sdk-test-view-pk-cs/sdk-test-view-pk-cs.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <!--
+    Use local package sources instead of published ones.
+    This makes integration test somewhat differ from production configuration, but
+    at least it simplifies workflow for editing and testing C# code itself.
+  -->
+  <ItemGroup>
+    <ProjectReference Include="../../crates/bindings-csharp/Codegen/Codegen.csproj" OutputItemType="Analyzer" ReferenceOutputAssembly="false" />
+    <ProjectReference Include="../../crates/bindings-csharp/Runtime/Runtime.csproj" />
+  </ItemGroup>
+
+</Project>