Linq: Adds support constant evaluation of Nullable<T>.HasValue

Microsoft.Azure.Cosmos/src/Linq/SubtreeEvaluator.cs

@@ -13,7 +13,7 @@ namespace Microsoft.Azure.Cosmos.Linq
     /// </summary> 
     internal sealed class SubtreeEvaluator : ExpressionVisitor
     {
-        private HashSet<Expression> candidates;
+        private readonly HashSet<Expression> candidates;
 
         public SubtreeEvaluator(HashSet<Expression> candidates)
         {
@@ -72,12 +72,28 @@ private Expression EvaluateMemberAccess(Expression expression)
             ConstantExpression targetConstant = targetExpression as ConstantExpression;
 
             // If we have a target expression but it cannot be resolved to a constant, then we should skip
-            // using reflectoin here and instead rely on the fallback delegate compilation approach.
+            // using reflection here and instead rely on the fallback delegate compilation approach.
             if (targetExpression is not null && targetConstant is null)
             {
                 return expression;
             }
 
+            // We need special handling for Nullable<T>.HasValue. This is because most reflection
+            // methods, including property and field accessors, pass instance arguments as object type.
+            // Nullable<T> has special runtime behavior that boxes the value of the nullable instead of the
+            // nullable struct itself. When Nullable<T>.HasValue is false, it is boxed as a null value when
+            // passed to the PropertyInfo/FieldInfo.GetValue. This causes a TargetException to be thrown since
+            // we are trying to evaluate an instance property with a null target.
+            if (targetConstant != null &&
+                targetConstant.Value == null &&
+                Nullable.GetUnderlyingType(targetConstant.Type) != null &&
+                memberExpression.Member.Name == "HasValue")
+            {
+                // So, if we're calling Nullable<T>.HasValue and targetConstant.Value is null, that means HasValue
+                // would return false. Do that here to work around reflection quirks
+                return Expression.Constant(false);
+            }
+
             if (memberExpression.Member is FieldInfo fieldInfo)
             {
                 return Expression.Constant(fieldInfo.GetValue(targetConstant?.Value), memberExpression.Type);

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.EmulatorTests/BaselineTest/TestBaseline/LinqTranslationBaselineTests.TestMemberAccessWithNullableTypes.xml

@@ -0,0 +1,50 @@
+<Results>
+  <Result>
+    <Input>
+      <Description><![CDATA[Filter on null double?]]></Description>
+      <Expression><![CDATA[query.Where(doc => (DisplayClass.nullDouble.HasValue AndAlso (Convert(doc.NumericField, Nullable`1) > DisplayClass.nullDouble)))]]></Expression>
+    </Input>
+    <Output>
+      <SqlQuery><![CDATA[
+SELECT VALUE root 
+FROM root 
+WHERE (false AND (root["NumericField"] > null))]]></SqlQuery>
+    </Output>
+  </Result>
+  <Result>
+    <Input>
+      <Description><![CDATA[Filter on false double?]]></Description>
+      <Expression><![CDATA[query.Where(doc => (DisplayClass.zeroDouble.HasValue AndAlso (Convert(doc.NumericField, Nullable`1) > DisplayClass.zeroDouble)))]]></Expression>
+    </Input>
+    <Output>
+      <SqlQuery><![CDATA[
+SELECT VALUE root 
+FROM root 
+WHERE (true AND (root["NumericField"] > 0))]]></SqlQuery>
+    </Output>
+  </Result>
+  <Result>
+    <Input>
+      <Description><![CDATA[Filter on null bool?]]></Description>
+      <Expression><![CDATA[query.Where(doc => (DisplayClass.nullBool.HasValue AndAlso (Convert(doc.BooleanField, Nullable`1) == DisplayClass.nullBool)))]]></Expression>
+    </Input>
+    <Output>
+      <SqlQuery><![CDATA[
+SELECT VALUE root 
+FROM root 
+WHERE (false AND (root["BooleanField"] = null))]]></SqlQuery>
+    </Output>
+  </Result>
+  <Result>
+    <Input>
+      <Description><![CDATA[Filter on false bool?]]></Description>
+      <Expression><![CDATA[query.Where(doc => (DisplayClass.zeroDouble.HasValue AndAlso (Convert(doc.BooleanField, Nullable`1) == DisplayClass.falseBool)))]]></Expression>
+    </Input>
+    <Output>
+      <SqlQuery><![CDATA[
+SELECT VALUE root 
+FROM root 
+WHERE (true AND (root["BooleanField"] = false))]]></SqlQuery>
+    </Output>
+  </Result>
+</Results>

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.EmulatorTests/LinqTranslationBaselineTests.cs

@@ -112,6 +112,9 @@ internal class DataObject : LinqTestObject
             public List<int> EnumerableField;
             public Point Point;
             public int? NullableField;
+#pragma warning disable CS0649 // Field is never assigned to, and will always have its default value false
+            public bool BooleanField;
+#pragma warning restore // Field is never assigned to, and will always have its default value false
 
             [JsonConverter(typeof(StringEnumConverter))]
             public TestEnum EnumField1;
@@ -588,7 +591,6 @@ public void TestMathFunctions()
             this.ExecuteTestSuite(inputs);
         }
 
-
         [TestMethod]
         public void TestMemberAccess()
         {
@@ -619,6 +621,28 @@ public void TestMemberAccess()
             this.ExecuteTestSuite(inputs);
         }
 
+        [TestMethod]
+        public void TestMemberAccessWithNullableTypes()
+        {
+            List<DataObject> testData = new();
+            IOrderedQueryable<DataObject> constantQuery = testContainer.GetItemLinqQueryable<DataObject>(allowSynchronousQueryExecution: true);
+            Func<bool, IQueryable<DataObject>> getQuery = useQuery => useQuery ? constantQuery : testData.AsQueryable();
+
+            double? nullDouble = null;
+            double? zeroDouble = 0;
+            bool? nullBool = null;
+            bool? falseBool = false;
+
+            List<LinqTestInput> inputs = new()
+            {
+                new LinqTestInput("Filter on null double?", b => getQuery(b).Where(doc => nullDouble.HasValue && doc.NumericField > nullDouble)),
+                new LinqTestInput("Filter on false double?", b => getQuery(b).Where(doc => zeroDouble.HasValue && doc.NumericField > zeroDouble)),
+                new LinqTestInput("Filter on null bool?", b => getQuery(b).Where(doc => nullBool.HasValue && doc.BooleanField == nullBool)),
+                new LinqTestInput("Filter on false bool?", b => getQuery(b).Where(doc => zeroDouble.HasValue && doc.BooleanField == falseBool)),
+            };
+            this.ExecuteTestSuite(inputs);
+        }
+
         private Func<bool, IQueryable<DataObject>> CreateDataTestStringFunctions()
         {
             const int Records = 100;

Microsoft.Azure.Cosmos/tests/Microsoft.Azure.Cosmos.EmulatorTests/Microsoft.Azure.Cosmos.EmulatorTests.csproj

@@ -35,6 +35,7 @@
     <None Remove="BaselineTest\TestBaseline\EndToEndTraceWriterBaselineTests.StreamPointOperationsAsync.xml" />
     <None Remove="BaselineTest\TestBaseline\EndToEndTraceWriterBaselineTests.TypedPointOperationsAsync.xml" />
     <None Remove="BaselineTest\TestBaseline\LinqTranslationBaselineTests.TestDateTimeJsonConverterTimezones.xml" />
+    <None Remove="BaselineTest\TestBaseline\LinqTranslationBaselineTests.TestMemberAccessWithNullableTypes.xml" />
   </ItemGroup>
 
   <ItemGroup>
@@ -193,6 +194,9 @@
     <Content Include="BaselineTest\TestBaseline\LinqTranslationBaselineTests.TestDateTimeJsonConverterTimezones.xml">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>
+    <Content Include="BaselineTest\TestBaseline\LinqTranslationBaselineTests.TestMemberAccessWithNullableTypes.xml">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
     <Content Include="BaselineTest\TestBaseline\LinqTranslationBaselineTests.TestSelectTop.xml">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </Content>