Fix to #20759 - Query: client eval followed by aggregate operation th…

…rows KeyNotFoundException: The given key 'EmptyProjectionMember' was not present in the dictionary.

Problem is that when client eval happens in the projection before the aggregate operation SelectExpression projection mapping can/will be empty. However when we try to access them using GetMappedProjection we assume that we always find what we want.
Fix is to check that selectExpression.Projection is empty. Otherwise we know client eval happened and we can't translate aggregate.

Fixes #20759

src/EFCore.Relational/Query/RelationalQueryableMethodTranslatingExpressionVisitor.cs

@@ -223,9 +223,16 @@ protected override ShapedQueryExpression TranslateAverage(ShapedQueryExpression
 
             var newSelector = selector == null
                 || selector.Body == selector.Parameters[0]
-                    ? selectExpression.GetMappedProjection(new ProjectionMember())
+                    ? selectExpression.Projection.Count == 0
+                        ? selectExpression.GetMappedProjection(new ProjectionMember())
+                        : null
                     : RemapLambdaBody(source, selector);
 
+            if (newSelector == null)
+            {
+                return null;
+            }
+
             var projection = _sqlTranslator.TranslateAverage(newSelector);
             return projection != null
                 ? AggregateResultShaper(source, projection, throwWhenEmpty: true, resultType)
@@ -683,9 +690,16 @@ protected override ShapedQueryExpression TranslateMax(ShapedQueryExpression sour
 
             var newSelector = selector == null
                 || selector.Body == selector.Parameters[0]
-                    ? selectExpression.GetMappedProjection(new ProjectionMember())
+                    ? selectExpression.Projection.Count == 0
+                        ? selectExpression.GetMappedProjection(new ProjectionMember())
+                        : null
                     : RemapLambdaBody(source, selector);
 
+            if (newSelector == null)
+            {
+                return null;
+            }
+
             var projection = _sqlTranslator.TranslateMax(newSelector);
 
             return AggregateResultShaper(source, projection, throwWhenEmpty: true, resultType);
@@ -701,9 +715,16 @@ protected override ShapedQueryExpression TranslateMin(ShapedQueryExpression sour
 
             var newSelector = selector == null
                 || selector.Body == selector.Parameters[0]
-                    ? selectExpression.GetMappedProjection(new ProjectionMember())
+                    ? selectExpression.Projection.Count == 0
+                        ? selectExpression.GetMappedProjection(new ProjectionMember())
+                        : null
                     : RemapLambdaBody(source, selector);
 
+            if (newSelector == null)
+            {
+                return null;
+            }
+
             var projection = _sqlTranslator.TranslateMin(newSelector);
 
             return AggregateResultShaper(source, projection, throwWhenEmpty: true, resultType);
@@ -1028,11 +1049,19 @@ protected override ShapedQueryExpression TranslateSum(ShapedQueryExpression sour
 
             var selectExpression = (SelectExpression)source.QueryExpression;
             selectExpression.PrepareForAggregate();
+
             var newSelector = selector == null
                 || selector.Body == selector.Parameters[0]
-                    ? selectExpression.GetMappedProjection(new ProjectionMember())
+                    ? selectExpression.Projection.Count == 0
+                        ? selectExpression.GetMappedProjection(new ProjectionMember())
+                        : null
                     : RemapLambdaBody(source, selector);
 
+            if (newSelector == null)
+            {
+                return null;
+            }
+
             var projection = _sqlTranslator.TranslateSum(newSelector);
             return projection != null
                 ? AggregateResultShaper(source, projection, throwWhenEmpty: false, resultType)

test/EFCore.InMemory.FunctionalTests/Query/GearsOfWarQueryInMemoryTest.cs

@@ -88,5 +88,11 @@ public override Task Enum_closure_typed_as_underlying_type_generates_correct_par
         {
             return base.Enum_closure_typed_as_underlying_type_generates_correct_parameter_type(async);
         }
+
+        [ConditionalTheory(Skip = "issue #17386")]
+        public override Task Client_eval_followed_by_set_operation_throws_meaningful_exception(bool async)
+        {
+            return base.Client_eval_followed_by_set_operation_throws_meaningful_exception(async);
+        }
     }
 }

test/EFCore.Specification.Tests/Query/GearsOfWarQueryTestBase.cs

@@ -7481,6 +7481,31 @@ public virtual Task Enum_array_contains(bool async)
                     .Where(w => w.SynergyWith != null && types.Contains(w.SynergyWith.AmmunitionType)));
         }
 
+        [ConditionalTheory]
+        [MemberData(nameof(IsAsyncData))]
+        public virtual async Task Client_eval_followed_by_set_operation_throws_meaningful_exception(bool async)
+        {
+            await AssertTranslationFailed(
+                () => AssertSum(
+                    async,
+                    ss => ss.Set<Mission>().Select(m => m.Duration.Ticks)));
+
+            await AssertTranslationFailed(
+                () => AssertAverage(
+                    async,
+                    ss => ss.Set<Mission>().Select(m => m.Duration.Ticks)));
+
+            await AssertTranslationFailed(
+                () => AssertMin(
+                    async,
+                    ss => ss.Set<Mission>().Select(m => m.Duration.Ticks)));
+
+            await AssertTranslationFailed(
+                () => AssertMax(
+                    async,
+                    ss => ss.Set<Mission>().Select(m => m.Duration.Ticks)));
+        }
+
         protected GearsOfWarContext CreateContext() => Fixture.CreateContext();
 
         protected virtual void ClearLog()