Redo NpgsqlSetOperationTypingInjector (#3291)

Fixes #3283

src/EFCore.PG/Query/Internal/NpgsqlQueryTranslationPostprocessor.cs

@@ -35,7 +35,7 @@ public override Expression Process(Expression query)
         var result = base.Process(query);
 
         result = new NpgsqlUnnestPostprocessor().Visit(result);
-        result = new NpgsqlSetOperationTypeResolutionCompensatingExpressionVisitor().Visit(result);
+        result = new NpgsqlSetOperationTypingInjector().Visit(result);
 
         return result;
     }

src/EFCore.PG/Query/Internal/NpgsqlSetOperationTypingInjector.cs

@@ -0,0 +1,80 @@
+namespace Npgsql.EntityFrameworkCore.PostgreSQL.Query.Internal;
+
+/// <summary>
+///     A visitor that injects explicit typing on null projections in set operations, to ensure PostgreSQL gets the typing right.
+/// </summary>
+/// <remarks>
+///     <para>
+///         See the <see href="https://www.postgresql.org/docs/current/typeconv-union-case.html">
+///         PostgreSQL docs on type conversion and set operations</see>.
+///     </para>
+///     <para>
+///         This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+///         the same compatibility standards as public APIs. It may be changed or removed without notice in
+///         any release. You should only use it directly in your code with extreme caution and knowing that
+///         doing so can result in application failures when updating to a new Entity Framework Core release.
+///     </para>
+/// </remarks>
+public class NpgsqlSetOperationTypingInjector : ExpressionVisitor
+{
+    /// <summary>
+    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+    ///     any release. You should only use it directly in your code with extreme caution and knowing that
+    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
+    /// </summary>
+    protected override Expression VisitExtension(Expression extensionExpression)
+        => extensionExpression switch
+        {
+            ShapedQueryExpression shapedQueryExpression
+                => shapedQueryExpression.Update(
+                    Visit(shapedQueryExpression.QueryExpression),
+                    Visit(shapedQueryExpression.ShaperExpression)),
+
+            SetOperationBase setOperationExpression => VisitSetOperation(setOperationExpression),
+
+            _ => base.VisitExtension(extensionExpression)
+        };
+
+    private Expression VisitSetOperation(SetOperationBase setOperation)
+    {
+        var select1 = (SelectExpression)Visit(setOperation.Source1);
+        var select2 = (SelectExpression)Visit(setOperation.Source2);
+
+        List<ProjectionExpression>? rewrittenProjections = null;
+
+        for (var i = 0; i < select1.Projection.Count; i++)
+        {
+            var projection = select1.Projection[i];
+            var visitedProjection = projection.Expression is SqlConstantExpression { Value : null }
+                && select2.Projection[i].Expression is SqlConstantExpression { Value : null }
+                ? projection.Update(
+                    new SqlUnaryExpression(
+                        ExpressionType.Convert, projection.Expression, projection.Expression.Type, projection.Expression.TypeMapping))
+                : (ProjectionExpression)Visit(projection);
+
+            if (visitedProjection != projection && rewrittenProjections is null)
+            {
+                rewrittenProjections = new List<ProjectionExpression>(select1.Projection.Count);
+                rewrittenProjections.AddRange(select1.Projection.Take(i));
+            }
+
+            rewrittenProjections?.Add(visitedProjection);
+        }
+
+        if (rewrittenProjections is not null)
+        {
+            select1 = select1.Update(
+                select1.Tables,
+                select1.Predicate,
+                select1.GroupBy,
+                select1.Having,
+                rewrittenProjections,
+                select1.Orderings,
+                select1.Offset,
+                select1.Limit);
+        }
+
+        return setOperation.Update(select1, select2);
+    }
+}

test/EFCore.PG.FunctionalTests/Query/EntitySplittingQueryNpgsqlTest.cs

@@ -449,7 +449,7 @@ public override async Task Tpc_entity_owning_a_split_reference_on_leaf_with_tabl
             """
 SELECT u."Id", u."BaseValue", u."MiddleValue", u."SiblingValue", u."LeafValue", u."Discriminator", l0."Id", l0."OwnedReference_Id", l0."OwnedReference_OwnedIntValue1", l0."OwnedReference_OwnedIntValue2", o0."OwnedIntValue3", o."OwnedIntValue4", l0."OwnedReference_OwnedStringValue1", l0."OwnedReference_OwnedStringValue2", o0."OwnedStringValue3", o."OwnedStringValue4"
 FROM (
-    SELECT b."Id", b."BaseValue", NULL::int AS "MiddleValue", NULL::int AS "SiblingValue", NULL::int AS "LeafValue", 'BaseEntity' AS "Discriminator"
+    SELECT b."Id", b."BaseValue", NULL AS "MiddleValue", NULL::int AS "SiblingValue", NULL::int AS "LeafValue", 'BaseEntity' AS "Discriminator"
     FROM "BaseEntity" AS b
     UNION ALL
     SELECT m."Id", m."BaseValue", m."MiddleValue", NULL AS "SiblingValue", NULL AS "LeafValue", 'MiddleEntity' AS "Discriminator"
@@ -578,7 +578,7 @@ public override async Task Tpc_entity_owning_a_split_reference_on_base_without_t
             """
 SELECT u."Id", u."BaseValue", u."MiddleValue", u."SiblingValue", u."LeafValue", u."Discriminator", o."BaseEntityId", o."Id", o."OwnedIntValue1", o."OwnedIntValue2", o1."OwnedIntValue3", o0."OwnedIntValue4", o."OwnedStringValue1", o."OwnedStringValue2", o1."OwnedStringValue3", o0."OwnedStringValue4"
 FROM (
-    SELECT b."Id", b."BaseValue", NULL::int AS "MiddleValue", NULL::int AS "SiblingValue", NULL::int AS "LeafValue", 'BaseEntity' AS "Discriminator"
+    SELECT b."Id", b."BaseValue", NULL AS "MiddleValue", NULL::int AS "SiblingValue", NULL::int AS "LeafValue", 'BaseEntity' AS "Discriminator"
     FROM "BaseEntity" AS b
     UNION ALL
     SELECT m."Id", m."BaseValue", m."MiddleValue", NULL AS "SiblingValue", NULL AS "LeafValue", 'MiddleEntity' AS "Discriminator"
@@ -620,7 +620,7 @@ public override async Task Tpc_entity_owning_a_split_reference_on_middle_without
             """
 SELECT u."Id", u."BaseValue", u."MiddleValue", u."SiblingValue", u."LeafValue", u."Discriminator", o."MiddleEntityId", o."Id", o."OwnedIntValue1", o."OwnedIntValue2", o1."OwnedIntValue3", o0."OwnedIntValue4", o."OwnedStringValue1", o."OwnedStringValue2", o1."OwnedStringValue3", o0."OwnedStringValue4"
 FROM (
-    SELECT b."Id", b."BaseValue", NULL::int AS "MiddleValue", NULL::int AS "SiblingValue", NULL::int AS "LeafValue", 'BaseEntity' AS "Discriminator"
+    SELECT b."Id", b."BaseValue", NULL AS "MiddleValue", NULL::int AS "SiblingValue", NULL::int AS "LeafValue", 'BaseEntity' AS "Discriminator"
     FROM "BaseEntity" AS b
     UNION ALL
     SELECT m."Id", m."BaseValue", m."MiddleValue", NULL AS "SiblingValue", NULL AS "LeafValue", 'MiddleEntity' AS "Discriminator"
@@ -686,7 +686,7 @@ public override async Task Tpc_entity_owning_a_split_collection_on_base(bool asy
             """
 SELECT u."Id", u."BaseValue", u."MiddleValue", u."SiblingValue", u."LeafValue", u."Discriminator", s0."BaseEntityId", s0."Id", s0."OwnedIntValue1", s0."OwnedIntValue2", s0."OwnedIntValue3", s0."OwnedIntValue4", s0."OwnedStringValue1", s0."OwnedStringValue2", s0."OwnedStringValue3", s0."OwnedStringValue4"
 FROM (
-    SELECT b."Id", b."BaseValue", NULL::int AS "MiddleValue", NULL::int AS "SiblingValue", NULL::int AS "LeafValue", 'BaseEntity' AS "Discriminator"
+    SELECT b."Id", b."BaseValue", NULL AS "MiddleValue", NULL::int AS "SiblingValue", NULL::int AS "LeafValue", 'BaseEntity' AS "Discriminator"
     FROM "BaseEntity" AS b
     UNION ALL
     SELECT m."Id", m."BaseValue", m."MiddleValue", NULL AS "SiblingValue", NULL AS "LeafValue", 'MiddleEntity' AS "Discriminator"
@@ -732,7 +732,7 @@ public override async Task Tpc_entity_owning_a_split_collection_on_middle(bool a
             """
 SELECT u."Id", u."BaseValue", u."MiddleValue", u."SiblingValue", u."LeafValue", u."Discriminator", s0."MiddleEntityId", s0."Id", s0."OwnedIntValue1", s0."OwnedIntValue2", s0."OwnedIntValue3", s0."OwnedIntValue4", s0."OwnedStringValue1", s0."OwnedStringValue2", s0."OwnedStringValue3", s0."OwnedStringValue4"
 FROM (
-    SELECT b."Id", b."BaseValue", NULL::int AS "MiddleValue", NULL::int AS "SiblingValue", NULL::int AS "LeafValue", 'BaseEntity' AS "Discriminator"
+    SELECT b."Id", b."BaseValue", NULL AS "MiddleValue", NULL::int AS "SiblingValue", NULL::int AS "LeafValue", 'BaseEntity' AS "Discriminator"
     FROM "BaseEntity" AS b
     UNION ALL
     SELECT m."Id", m."BaseValue", m."MiddleValue", NULL AS "SiblingValue", NULL AS "LeafValue", 'MiddleEntity' AS "Discriminator"