Design Meeting Notes January 14, 2016

UWP, EF, and .NET Native

RC2 will bring improved support for EF on Universal Windows Platform.

Scaffold-Directives powershell command

Most .NET Native errors can be resolved by adding the right runtime directive (rdxml) to the project. To simplify, we are introducing a tool that will automate rdxml generation. The new powershell command Scaffold-Directives generates (most of) the rdxml necessary for .NET Native.

How it generates rdxml

The command compiles the user's project and loads all DbContext types in the project. RuntimeTypeDiscoverer loads the model and executes logic to determine what kinds of generic types may exist at runtime.

One step in this logic is scanning all loaded assemblies for the attribute [CallsMakeGenericMethod()]. This attribute should be declared on all methods that make use of MakeGenericMethod. Based on the arguments in the attribute and the user's model, RuntimeTypeDiscoverer will attempt to construct the generic method and include the appropriate rdxml for this type.

CallsMakeGenericMethod accepts placeholder types that can be used to represent user types. See TypeArgumentCategory

Example: from PropertiesAccessorFactory, See source here

        [CallsMakeGenericMethod(nameof(CreateGeneric), typeof(TypeArgumentCategory.Properties))]
        [CallsMakeGenericMethod(nameof(CreateGeneric), typeof(HashSet<object>))]
        public virtual PropertyAccessors Create([NotNull] IPropertyBase propertyBase)
            => (PropertyAccessors)typeof(PropertyAccessorsFactory).GetTypeInfo().GetDeclaredMethod(nameof(CreateGeneric))
                .MakeGenericMethod((propertyBase as IProperty)?.ClrType
                                   ?? (((INavigation)propertyBase).IsCollection()
                                       ? typeof(HashSet<object>)
                                       : typeof(object)))
                .Invoke(null, new object[] { propertyBase });

        private static PropertyAccessors CreateGeneric<TProperty>(IPropertyBase propertyBase)
        {
            // ...
        }

Contributors beware: unsafe API calls

Our code makes use of APIs that are unsafe to use on .NET Native without runtime directives. The following calls should be avoided if possible. Where used, RuntimeTypeDiscoverer may need to be altered to account for possible types that can be constructed at runtime.

• System.Reflection.MethodInfo.MakeGenericMethod()
• System.Type.MakeGenericType()
• System.Linq.Expressions.Expression.Lambda()