Allow value converters to convert nulls

Fixes #13850

src/EFCore.Cosmos/Query/Internal/CosmosShapedQueryCompilingExpressionVisitor.CosmosProjectionBindingRemovingExpressionVisitorBase.cs

@@ -712,13 +712,31 @@ var body
                         body = Expression.Convert(body, type);
                     }
 
+                    Expression replaceExpression;
+                    if (converter?.ConvertsNulls == true)
+                    {
+                        replaceExpression = ReplacingExpressionVisitor.Replace(
+                            converter.ConvertFromProviderExpression.Parameters.Single(),
+                            Expression.Default(converter.ProviderClrType),
+                            converter.ConvertFromProviderExpression.Body);
+
+                        if (replaceExpression.Type != type)
+                        {
+                            replaceExpression = Expression.Convert(replaceExpression, type);
+                        }
+                    }
+                    else
+                    {
+                        replaceExpression = Expression.Default(type);
+                    }
+
                     body = Expression.Condition(
                         Expression.OrElse(
                             Expression.Equal(jTokenParameter, Expression.Default(typeof(JToken))),
                             Expression.Equal(
                                 Expression.MakeMemberAccess(jTokenParameter, _jTokenTypePropertyInfo),
                                 Expression.Constant(JTokenType.Null))),
-                        Expression.Default(type),
+                        replaceExpression,
                         body);
 
                     valueExpression = Expression.Invoke(Expression.Lambda(body, jTokenParameter), jTokenExpression);

src/EFCore.Design/Migrations/Design/CSharpSnapshotGenerator.cs

@@ -1570,8 +1570,7 @@ private void GenerateFluentApiForDefaultValue(
             IProperty property,
             IndentedStringBuilder stringBuilder)
         {
-            var defaultValue = property.GetDefaultValue();
-            if (defaultValue == null)
+            if (!property.TryGetDefaultValue(out var defaultValue))
             {
                 return;
             }

src/EFCore.Design/Scaffolding/Internal/CSharpDbContextGenerator.cs

@@ -621,17 +621,19 @@ private void GenerateProperty(IProperty property, bool useDataAnnotations)
                 }
             }
 
-            var defaultValue = property.GetDefaultValue();
-            if (defaultValue == DBNull.Value)
+            if (property.TryGetDefaultValue(out var defaultValue))
             {
-                lines.Add($".{nameof(RelationalPropertyBuilderExtensions.HasDefaultValue)}()");
-                annotations.Remove(RelationalAnnotationNames.DefaultValue);
-            }
-            else if (defaultValue != null)
-            {
-                lines.Add(
-                    $".{nameof(RelationalPropertyBuilderExtensions.HasDefaultValue)}({_code.UnknownLiteral(defaultValue)})");
-                annotations.Remove(RelationalAnnotationNames.DefaultValue);
+                if (defaultValue == DBNull.Value)
+                {
+                    lines.Add($".{nameof(RelationalPropertyBuilderExtensions.HasDefaultValue)}()");
+                    annotations.Remove(RelationalAnnotationNames.DefaultValue);
+                }
+                else if (defaultValue != null)
+                {
+                    lines.Add(
+                        $".{nameof(RelationalPropertyBuilderExtensions.HasDefaultValue)}({_code.UnknownLiteral(defaultValue)})");
+                    annotations.Remove(RelationalAnnotationNames.DefaultValue);
+                }
             }
 
             var valueGenerated = property.ValueGenerated;

src/EFCore.Relational/Extensions/RelationalPropertyExtensions.cs

@@ -385,7 +385,7 @@ public static void SetColumnType(this IMutableProperty property, string? value)
         /// <returns> The default columns to which the property would be mapped. </returns>
         public static IEnumerable<IColumnMappingBase> GetDefaultColumnMappings(this IProperty property)
             => (IEnumerable<IColumnMappingBase>?)property.FindRuntimeAnnotationValue(
-                RelationalAnnotationNames.DefaultColumnMappings)
+                    RelationalAnnotationNames.DefaultColumnMappings)
                 ?? Enumerable.Empty<IColumnMappingBase>();
 
         /// <summary>
@@ -395,7 +395,7 @@ public static IEnumerable<IColumnMappingBase> GetDefaultColumnMappings(this IPro
         /// <returns> The table columns to which the property is mapped. </returns>
         public static IEnumerable<IColumnMapping> GetTableColumnMappings(this IProperty property)
             => (IEnumerable<IColumnMapping>?)property.FindRuntimeAnnotationValue(
-                RelationalAnnotationNames.TableColumnMappings)
+                    RelationalAnnotationNames.TableColumnMappings)
                 ?? Enumerable.Empty<IColumnMapping>();
 
         /// <summary>
@@ -405,7 +405,7 @@ public static IEnumerable<IColumnMapping> GetTableColumnMappings(this IProperty
         /// <returns> The view columns to which the property is mapped. </returns>
         public static IEnumerable<IViewColumnMapping> GetViewColumnMappings(this IProperty property)
             => (IEnumerable<IViewColumnMapping>?)property.FindRuntimeAnnotationValue(
-                RelationalAnnotationNames.ViewColumnMappings)
+                    RelationalAnnotationNames.ViewColumnMappings)
                 ?? Enumerable.Empty<IViewColumnMapping>();
 
         /// <summary>
@@ -415,7 +415,7 @@ public static IEnumerable<IViewColumnMapping> GetViewColumnMappings(this IProper
         /// <returns> The SQL query columns to which the property is mapped. </returns>
         public static IEnumerable<ISqlQueryColumnMapping> GetSqlQueryColumnMappings(this IProperty property)
             => (IEnumerable<ISqlQueryColumnMapping>?)property.FindRuntimeAnnotationValue(
-                RelationalAnnotationNames.SqlQueryColumnMappings)
+                    RelationalAnnotationNames.SqlQueryColumnMappings)
                 ?? Enumerable.Empty<ISqlQueryColumnMapping>();
 
         /// <summary>
@@ -425,7 +425,7 @@ public static IEnumerable<ISqlQueryColumnMapping> GetSqlQueryColumnMappings(this
         /// <returns> The function columns to which the property is mapped. </returns>
         public static IEnumerable<IFunctionColumnMapping> GetFunctionColumnMappings(this IProperty property)
             => (IEnumerable<IFunctionColumnMapping>?)property.FindRuntimeAnnotationValue(
-                RelationalAnnotationNames.FunctionColumnMappings)
+                    RelationalAnnotationNames.FunctionColumnMappings)
                 ?? Enumerable.Empty<IFunctionColumnMapping>();
 
         /// <summary>
@@ -701,7 +701,30 @@ public static void SetIsStored(this IMutableProperty property, bool? value)
         /// <param name="property"> The property. </param>
         /// <returns> The object that is used as the default value for the column this property is mapped to. </returns>
         public static object? GetDefaultValue(this IReadOnlyProperty property)
-            => property.FindAnnotation(RelationalAnnotationNames.DefaultValue)?.Value;
+        {
+            property.TryGetDefaultValue(out var defaultValue);
+            return defaultValue;
+        }
+
+        /// <summary>
+        ///     Returns the object that is used as the default value for the column this property is mapped to.
+        /// </summary>
+        /// <param name="property"> The property. </param>
+        /// <param name="defaultValue"> The default value, or the CLR default if no explicit default has been set. </param>
+        /// <returns> The object that is used as the default value for the column this property is mapped to. </returns>
+        public static bool TryGetDefaultValue(this IReadOnlyProperty property, out object? defaultValue)
+        {
+            var annotation = property.FindAnnotation(RelationalAnnotationNames.DefaultValue);
+
+            if (annotation != null)
+            {
+                defaultValue = annotation.Value;
+                return defaultValue != null;
+            }
+
+            defaultValue = property.ClrType.GetDefaultValue();
+            return false;
+        }
 
         /// <summary>
         ///     Returns the object that is used as the default value for the column this property is mapped to.
@@ -710,20 +733,38 @@ public static void SetIsStored(this IMutableProperty property, bool? value)
         /// <param name="storeObject"> The identifier of the table-like store object containing the column. </param>
         /// <returns> The object that is used as the default value for the column this property is mapped to. </returns>
         public static object? GetDefaultValue(this IReadOnlyProperty property, in StoreObjectIdentifier storeObject)
+        {
+            property.TryGetDefaultValue(storeObject, out var defaultValue);
+            return defaultValue;
+        }
+
+        /// <summary>
+        ///     Returns the object that is used as the default value for the column this property is mapped to.
+        /// </summary>
+        /// <param name="property"> The property. </param>
+        /// <param name="storeObject"> The identifier of the table-like store object containing the column. </param>
+        /// <param name="defaultValue"> The default value, or the CLR default if no explicit default has been set. </param>
+        /// <returns> The object that is used as the default value for the column this property is mapped to. </returns>
+        public static bool TryGetDefaultValue(
+            this IReadOnlyProperty property,
+            in StoreObjectIdentifier storeObject,
+            out object? defaultValue)
         {
             var annotation = property.FindAnnotation(RelationalAnnotationNames.DefaultValue);
             if (annotation != null)
             {
-                return annotation.Value;
+                defaultValue = annotation.Value;
+                return defaultValue != null;
             }
 
             var sharedTableRootProperty = property.FindSharedStoreObjectRootProperty(storeObject);
             if (sharedTableRootProperty != null)
             {
-                return GetDefaultValue(sharedTableRootProperty, storeObject);
+                return TryGetDefaultValue(sharedTableRootProperty, storeObject, out defaultValue);
             }
 
-            return null;
+            defaultValue = property.ClrType.GetDefaultValue();
+            return false;
         }
 
         /// <summary>
@@ -982,7 +1023,10 @@ public static bool IsColumnNullable(this IReadOnlyProperty property, in StoreObj
                 || IsOptionalSharingDependent(property.DeclaringEntityType, storeObject, 0);
         }
 
-        private static bool IsOptionalSharingDependent(IReadOnlyEntityType entityType, in StoreObjectIdentifier storeObject, int recursionDepth)
+        private static bool IsOptionalSharingDependent(
+            IReadOnlyEntityType entityType,
+            in StoreObjectIdentifier storeObject,
+            int recursionDepth)
         {
             if (recursionDepth++ == Metadata.Internal.RelationalEntityTypeExtensions.MaxEntityTypesSharingTable)
             {
@@ -1277,7 +1321,8 @@ public static RelationalTypeMapping GetRelationalTypeMapping(this IReadOnlyPrope
         }
 
         private static IReadOnlyProperty? FindSharedObjectRootPrimaryKeyProperty(
-            IReadOnlyProperty property, in StoreObjectIdentifier storeObject)
+            IReadOnlyProperty property,
+            in StoreObjectIdentifier storeObject)
         {
             if (!property.IsPrimaryKey())
             {
@@ -1393,7 +1438,7 @@ public static RelationalTypeMapping GetRelationalTypeMapping(this IReadOnlyPrope
         /// <param name="storeObject"> The identifier of the table-like store object containing the column. </param>
         /// <returns> An object that stores property facet overrides. </returns>
         public static IAnnotatable? FindOverrides(this IProperty property, in StoreObjectIdentifier storeObject)
-            => (IAnnotatable?)RelationalPropertyOverrides.Find(property, storeObject);
+            => RelationalPropertyOverrides.Find(property, storeObject);
 
         /// <summary>
         ///     <para>
@@ -1410,7 +1455,7 @@ public static RelationalTypeMapping GetRelationalTypeMapping(this IReadOnlyPrope
         public static IMutableAnnotatable GetOrCreateOverrides(
             this IMutableProperty property,
             in StoreObjectIdentifier storeObject)
-            => (IMutableAnnotatable)RelationalPropertyOverrides.GetOrCreate(property, storeObject);
+            => RelationalPropertyOverrides.GetOrCreate(property, storeObject);
 
         /// <summary>
         ///     <para>
@@ -1427,6 +1472,6 @@ public static IMutableAnnotatable GetOrCreateOverrides(
         public static IConventionAnnotatable GetOrCreateOverrides(
             this IConventionProperty property,
             in StoreObjectIdentifier storeObject)
-            => (IConventionAnnotatable)RelationalPropertyOverrides.GetOrCreate(property, storeObject);
+            => RelationalPropertyOverrides.GetOrCreate(property, storeObject);
     }
 }

src/EFCore.Relational/Metadata/Conventions/RelationalValueGenerationConvention.cs

@@ -153,9 +153,9 @@ private void ProcessTableChanged(
             return valueGenerated
                 ?? (property.GetComputedColumnSql(storeObject) != null
                     ? ValueGenerated.OnAddOrUpdate
-                    : property.GetDefaultValue(storeObject) != null || property.GetDefaultValueSql(storeObject) != null
+                    : property.TryGetDefaultValue(storeObject, out _) || property.GetDefaultValueSql(storeObject) != null
                         ? ValueGenerated.OnAdd
-                        : (ValueGenerated?)null);
+                        : null);
         }
     }
 }

src/EFCore.Relational/Metadata/Conventions/StoreGenerationConvention.cs

@@ -115,7 +115,7 @@ protected virtual void Validate(
             IConventionProperty property,
             in StoreObjectIdentifier storeObject)
         {
-            if (property.GetDefaultValue(storeObject) != null)
+            if (property.TryGetDefaultValue(storeObject, out _))
             {
                 if (property.GetDefaultValueSql(storeObject) != null)
                 {

src/EFCore.Relational/Metadata/IColumn.cs

@@ -71,14 +71,33 @@ public virtual object? DefaultValue
         {
             get
             {
-                var property = PropertyMappings.First().Property;
-                var value = property.GetDefaultValue(StoreObjectIdentifier.Table(Table.Name, Table.Schema));
-                var converter = property.GetValueConverter() ?? PropertyMappings.First().TypeMapping?.Converter;
+                TryGetDefaultValue(out var defaultValue);
+                return defaultValue;
+            }
+        }
+
+        /// <summary>
+        ///     Gets the object that is used as the default value for this column.
+        /// </summary>
+        /// <param name="defaultValue"> The default value. </param>
+        /// <returns> True if the default value was explicitly set; false otherwise. </returns>
+        public virtual bool TryGetDefaultValue(out object? defaultValue)
+        {
+            var property = PropertyMappings.First().Property;
 
-                return converter != null
-                    ? converter.ConvertToProvider(value)
-                    : value;
+            if (!property.TryGetDefaultValue(StoreObjectIdentifier.Table(Table.Name, Table.Schema), out defaultValue))
+            {
+                return false;
+            }
+
+            var converter = property.GetValueConverter() ?? PropertyMappings.First().TypeMapping?.Converter;
+
+            if (converter != null)
+            {
+                defaultValue = converter.ConvertToProvider(defaultValue);
             }
+
+            return true;
         }
 
         /// <summary>