Add ability to set access for nested composite element

Fixes #370

+semver:breaking

Author: hazzik

src/FluentNHibernate.Testing/DomainModel/Mapping/ComponentElementPartTester.cs

@@ -37,6 +37,23 @@ public void CanSetParentReferenceAccess()
                 .HasAttribute("access", "backfield");
         }
 
+        [Test]
+        public void CanSetNestedCompositeElementAccessAccess()
+        {
+            var tester = new MappingTester<PropertyTarget>()
+                .ForMapping(m =>
+                    m.HasMany(x => x.Components)
+                        .Component(c =>
+                        {
+                            c.Map(x => x.Name);
+                            c.Component(target => target.MyParent, nested => nested.Access.BackingField());
+                        }));
+            tester
+                .Element("class/bag/composite-element/nested-composite-element").Exists()
+                .HasAttribute("name", "MyParent")
+                .HasAttribute("access", "backfield");
+        }
+
         [Test]
         public void CanCreateNestedCompositeElement()
         {

src/FluentNHibernate/Mapping/CompositeElementPart.cs

@@ -16,11 +16,11 @@ namespace FluentNHibernate.Mapping
     public class CompositeElementPart<T> : ICompositeElementMappingProvider, INestedCompositeElementMappingProvider
     {
         readonly Type entity;
-        readonly Member member;
+        private protected readonly Member member;
         readonly List<IPropertyMappingProvider> properties = new List<IPropertyMappingProvider>();
         readonly List<IManyToOneMappingProvider> references = new List<IManyToOneMappingProvider>();
         readonly List<INestedCompositeElementMappingProvider> components = new List<INestedCompositeElementMappingProvider>();
-        readonly AttributeStore attributes = new AttributeStore();
+        private protected readonly AttributeStore attributes = new AttributeStore();
 
         public CompositeElementPart(Type entity)
         {
@@ -164,9 +164,9 @@ void ParentReference(Member property, Access access)
         ///     });
         ///   });
         /// </example>
-        public void Component<TChild>(Expression<Func<T, TChild>> property, Action<CompositeElementPart<TChild>> nestedCompositeElementAction)
+        public void Component<TChild>(Expression<Func<T, TChild>> property, Action<NestedCompositeElementPart<TChild>> nestedCompositeElementAction)
         {
-            var nestedCompositeElement = new CompositeElementPart<TChild>(entity, property.ToMember());
+            var nestedCompositeElement = new NestedCompositeElementPart<TChild>(entity, property.ToMember());
 
             nestedCompositeElementAction(nestedCompositeElement);
 

src/FluentNHibernate/Mapping/NestedCompositeElementPart.cs

@@ -0,0 +1,28 @@
+using System;
+using FluentNHibernate.MappingModel;
+
+namespace FluentNHibernate.Mapping
+{
+    public class NestedCompositeElementPart<T> : CompositeElementPart<T>
+    {
+        public NestedCompositeElementPart(Type entity, Member member)
+            : base(entity, member)
+        {
+            Access = new AccessStrategyBuilder<NestedCompositeElementPart<T>>(this, value => attributes.Set("Access", Layer.UserSupplied, value));
+            
+            SetDefaultAccess();
+        }
+
+        public AccessStrategyBuilder<NestedCompositeElementPart<T>> Access { get; }
+        
+        void SetDefaultAccess()
+        {
+            var resolvedAccess = MemberAccessResolver.Resolve(member);
+
+            if (resolvedAccess == Mapping.Access.Property || resolvedAccess == Mapping.Access.Unset)
+                return; // property is the default so we don't need to specify it
+
+            attributes.Set("Access", Layer.Defaults, resolvedAccess.ToString());
+        }
+    }
+}

src/FluentNHibernate/MappingModel/Collections/NestedCompositeElementMapping.cs

@@ -24,6 +24,11 @@ public string Name
             get { return attributes.GetOrDefault<string>("Name"); }
         }
 
+        public string Access
+        {
+            get { return attributes.GetOrDefault<string>("Access"); }
+        }
+
         public void Set<T>(Expression<Func<NestedCompositeElementMapping, T>> expression, int layer, T value)
         {
             Set(expression.ToMember().Name, layer, value);

src/FluentNHibernate/MappingModel/Output/XmlCompositeElementWriter.cs

@@ -32,8 +32,13 @@ public override void ProcessCompositeElement(CompositeElementMapping mapping)
             if (mapping.IsSpecified("Class"))
                 element.WithAtt("class", mapping.Class);
 
-            if (mapping is NestedCompositeElementMapping)
-                element.WithAtt("name", ((NestedCompositeElementMapping)mapping).Name);
+            if (mapping is NestedCompositeElementMapping nested)
+            {
+                element.WithAtt("name", nested.Name);
+
+                if (mapping.IsSpecified("Access")) 
+                    element.WithAtt("access", nested.Access);
+            }
         }
 
         public override void Visit(CompositeElementMapping compositeElementMapping)