Remove usage of DeepClone

DeepClone uses BinaryFormatter which is obsolete in .NET 5.0 and throws a PlatformNotSupportedException.

The fix insures that columns are cloned instead of cloning the whole object

Fixes #479

+semver: fix

src/FluentNHibernate/Mapping/ComponentMap.cs

@@ -59,9 +59,7 @@ protected override ComponentMapping CreateComponentMappingRoot(AttributeStore st
 
         ExternalComponentMapping IExternalComponentMappingProvider.GetComponentMapping()
         {
-            var mapping = (ExternalComponentMapping)CreateComponentMapping();
-
-            return mapping.DeepClone();
+            return (ExternalComponentMapping) CreateComponentMapping();
         }
 
         Type IExternalComponentMappingProvider.Type

src/FluentNHibernate/Mapping/ElementPart.cs

@@ -101,7 +101,7 @@ ElementMapping IElementMappingProvider.GetElementMapping()
             foreach (var column in Columns)
             {
                 column.MergeAttributes(columnAttributes);
-                mapping.AddColumn(Layer.Defaults, column);
+                mapping.AddColumn(Layer.Defaults, column.Clone());
             }
 
             return mapping;

src/FluentNHibernate/Mapping/JoinedSubClassPart.cs

@@ -143,7 +143,7 @@ SubclassMapping ISubclassMappingProvider.GetSubclassMapping()
             mapping.Set(x => x.Type, Layer.Defaults, typeof(TSubclass));
 
             foreach (var column in columns)
-                mapping.Key.AddColumn(Layer.Defaults, column);
+                mapping.Key.AddColumn(Layer.Defaults, column.Clone());
 
             foreach (var property in providers.Properties)
                 mapping.AddProperty(property.GetPropertyMapping());

src/FluentNHibernate/Mapping/ManyToManyPart.cs

@@ -370,7 +370,7 @@ protected override CollectionMapping GetCollectionMapping()
                 collection.Key.AddColumn(Layer.Defaults, new ColumnMapping(EntityType.Name + "_id"));
 
             foreach (var column in parentKeyColumns)
-                collection.Key.AddColumn(Layer.UserSupplied, column);
+                collection.Key.AddColumn(Layer.UserSupplied, column.Clone());
 
             if (collection.Relationship != null)
             {
@@ -379,7 +379,7 @@ protected override CollectionMapping GetCollectionMapping()
                     ((ManyToManyMapping)collection.Relationship).AddColumn(Layer.Defaults, new ColumnMapping(typeof(TChild).Name + "_id"));
 
                 foreach (var column in childKeyColumns)
-                    ((ManyToManyMapping)collection.Relationship).AddColumn(Layer.UserSupplied, column);
+                    ((ManyToManyMapping)collection.Relationship).AddColumn(Layer.UserSupplied, column.Clone());
             }
 
             // HACK: Index only on list and map - shouldn't have to do this!

src/FluentNHibernate/Mapping/OneToManyPart.cs

@@ -198,7 +198,7 @@ protected override CollectionMapping GetCollectionMapping()
 
             foreach (var column in keyColumns)
             {
-                collection.Key.AddColumn(Layer.UserSupplied, column);
+                collection.Key.AddColumn(Layer.UserSupplied, column.Clone());
             }
 
             // HACK: shouldn't have to do this!

src/FluentNHibernate/Mapping/PropertyPart.cs

@@ -332,7 +332,7 @@ PropertyMapping IPropertyMappingProvider.GetPropertyMapping()
             }
 
             foreach (var column in columns)
-                mapping.AddColumn(Layer.UserSupplied, column);
+                mapping.AddColumn(Layer.UserSupplied, column.Clone());
 
             foreach (var column in mapping.Columns)
             {

src/FluentNHibernate/Mapping/SubclassMap.cs

@@ -345,7 +345,7 @@ SubclassMapping IIndeterminateSubclassMappingProvider.GetSubclassMapping(Subclas
                 }
             }
 
-            return mapping.DeepClone();
+            return mapping;
         }
 
         Type IIndeterminateSubclassMappingProvider.EntityType

src/FluentNHibernate/Utils/Extensions.cs

@@ -66,6 +66,7 @@ public static bool HasInterface(this Type type, Type interfaceType)
             return type.GetInterfaces().Contains(interfaceType);
         }
 
+        [Obsolete("Please do not use this method. It will be removed in a future version.")]
         public static T DeepClone<T>(this T obj)
         {
             using (var stream = new MemoryStream())