From 3d869fb6bc0d43d3840b1016b9645bdca1fcf1b4 Mon Sep 17 00:00:00 2001
From: Shay Rojansky <roji@roji.org>
Date: Wed, 16 Nov 2022 20:38:38 +0100
Subject: [PATCH] Detect DbFunction returning a nullable value expression
 (#29588)

Closes #29585
---
 .../Properties/RelationalStrings.Designer.cs  |  8 ++++++
 .../Properties/RelationalStrings.resx         |  3 ++
 .../RelationalMethodCallTranslatorProvider.cs | 11 +++++++-
 .../Query/UdfDbFunctionTestBase.cs            | 28 +++++++++++++++++++
 4 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/src/EFCore.Relational/Properties/RelationalStrings.Designer.cs b/src/EFCore.Relational/Properties/RelationalStrings.Designer.cs
index c412f98f98d..b7ef50f00fa 100644
--- a/src/EFCore.Relational/Properties/RelationalStrings.Designer.cs
+++ b/src/EFCore.Relational/Properties/RelationalStrings.Designer.cs
@@ -279,6 +279,14 @@ public static string DbFunctionNonScalarCustomTranslation(object? function)
                 GetString("DbFunctionNonScalarCustomTranslation", nameof(function)),
                 function);
 
+        /// <summary>
+        ///     The DbFunction '{function}' returns a SqlExpression of type '{type}', which is a nullable value type. DbFunctions must return expressions with non-nullable value types, even when they may return null.
+        /// </summary>
+        public static string DbFunctionNullableValueReturnType(object? function, object? type)
+            => string.Format(
+                GetString("DbFunctionNullableValueReturnType", nameof(function), nameof(type)),
+                function, type);
+
         /// <summary>
         ///     The default value SQL has not been specified for the column '{table}.{column}'. Specify the SQL before using Entity Framework to create the database schema.
         /// </summary>
diff --git a/src/EFCore.Relational/Properties/RelationalStrings.resx b/src/EFCore.Relational/Properties/RelationalStrings.resx
index 2b06d916915..d10d59b928c 100644
--- a/src/EFCore.Relational/Properties/RelationalStrings.resx
+++ b/src/EFCore.Relational/Properties/RelationalStrings.resx
@@ -217,6 +217,9 @@
   <data name="DbFunctionNonScalarCustomTranslation" xml:space="preserve">
     <value>Cannot set custom translation on the DbFunction '{function}' since it is not a scalar function.</value>
   </data>
+  <data name="DbFunctionNullableValueReturnType" xml:space="preserve">
+    <value>The DbFunction '{function}' returns a SqlExpression of type '{type}', which is a nullable value type. DbFunctions must return expressions with non-nullable value types, even when they may return null.</value>
+  </data>
   <data name="DefaultValueSqlUnspecified" xml:space="preserve">
     <value>The default value SQL has not been specified for the column '{table}.{column}'. Specify the SQL before using Entity Framework to create the database schema.</value>
   </data>
diff --git a/src/EFCore.Relational/Query/RelationalMethodCallTranslatorProvider.cs b/src/EFCore.Relational/Query/RelationalMethodCallTranslatorProvider.cs
index 566f3d12bf8..1de2f16a1f3 100644
--- a/src/EFCore.Relational/Query/RelationalMethodCallTranslatorProvider.cs
+++ b/src/EFCore.Relational/Query/RelationalMethodCallTranslatorProvider.cs
@@ -60,8 +60,17 @@ public RelationalMethodCallTranslatorProvider(RelationalMethodCallTranslatorProv
         {
             if (dbFunction.Translation != null)
             {
-                return dbFunction.Translation.Invoke(
+                var translation = dbFunction.Translation.Invoke(
                     arguments.Select(e => _sqlExpressionFactory.ApplyDefaultTypeMapping(e)).ToList());
+
+                if (translation.Type.IsNullableValueType())
+                {
+                    throw new InvalidOperationException(
+                        RelationalStrings.DbFunctionNullableValueReturnType(
+                            dbFunction.ModelName, dbFunction.ReturnType.ShortDisplayName()));
+                }
+
+                return translation;
             }
 
             var argumentsPropagateNullability = dbFunction.Parameters.Select(p => p.PropagatesNullability);
diff --git a/test/EFCore.Relational.Specification.Tests/Query/UdfDbFunctionTestBase.cs b/test/EFCore.Relational.Specification.Tests/Query/UdfDbFunctionTestBase.cs
index 9f524110d90..ce2cc778e72 100644
--- a/test/EFCore.Relational.Specification.Tests/Query/UdfDbFunctionTestBase.cs
+++ b/test/EFCore.Relational.Specification.Tests/Query/UdfDbFunctionTestBase.cs
@@ -224,6 +224,9 @@ public static string IdentityStringNonNullable(string s)
         public static string IdentityStringNonNullableFluent(string s)
             => throw new Exception();
 
+        public static int? NullableValueReturnType()
+            => throw new NotImplementedException();
+
         public string StringLength(string s)
             => throw new Exception();
 
@@ -310,6 +313,14 @@ protected override void OnModelCreating(ModelBuilder modelBuilder)
                         negated: false,
                         typeMapping: null));
 
+            modelBuilder.HasDbFunction(typeof(UDFSqlContext).GetMethod(nameof(NullableValueReturnType), Array.Empty<Type>()))
+                .HasTranslation(
+                    _ => new SqlFunctionExpression(
+                        "foo",
+                        nullable: true,
+                        typeof(int?),
+                        typeMapping: null));
+
             //Instance
             modelBuilder.HasDbFunction(typeof(UDFSqlContext).GetMethod(nameof(CustomerOrderCountInstance)))
                 .HasName("CustomerOrderCount");
@@ -1009,6 +1020,23 @@ public virtual void Scalar_Function_with_nested_InExpression_translation()
         Assert.Equal(4, query.Count);
     }
 
+#if RELEASE
+    [ConditionalFact]
+    public virtual void Scalar_Function_with_nullable_value_return_type_throws()
+    {
+        using var context = CreateContext();
+
+        var exception = Assert.Throws<InvalidOperationException>(
+            () => context.Customers.Where(c => c.Id == UDFSqlContext.NullableValueReturnType()).ToList());
+
+        Assert.Equal(
+            RelationalStrings.DbFunctionNullableValueReturnType(
+                "Microsoft.EntityFrameworkCore.Query.UdfDbFunctionTestBase<Microsoft.EntityFrameworkCore.Query.UdfDbFunctionSqlServerTests+SqlServer>+UDFSqlContext.NullableValueReturnType()",
+                "int?"),
+            exception.Message);
+    }
+#endif
+
     #endregion
 
     #region Instance