Entity Framework CascadeDelete using Data Annotations

CascadeDeleteAttribute.cs

using System;

[AttributeUsage(AttributeTargets.Property, AllowMultiple = false)]
public class CascadeDeleteAttribute : Attribute { }

CascadeDeleteAttributeConvention.cs

using System;
using System.Data.Entity.Core.Metadata.Edm;
using System.Data.Entity.Infrastructure;
using System.Data.Entity.ModelConfiguration.Conventions;
using System.Linq;
using System.Reflection;

public class CascadeDeleteAttributeConvention : IConceptualModelConvention<AssociationType>
{
    private static readonly Func<AssociationType, bool> IsSelfReferencing;
    private static readonly Func<AssociationType, bool> IsRequiredToMany;
    private static readonly Func<AssociationType, bool> IsManyToRequired;
    private static readonly Func<AssociationType, object> GetConfiguration;
    private static readonly Func<object, OperationAction?> NavigationPropertyConfigurationGetDeleteAction;

    static CascadeDeleteAttributeConvention()
    {
        var associationTypeExtensionsType = typeof(AssociationType).Assembly.GetType("System.Data.Entity.ModelConfiguration.Edm.AssociationTypeExtensions");
        var navigationPropertyConfigurationType = typeof(AssociationType).Assembly.GetType("System.Data.Entity.ModelConfiguration.Configuration.Properties.Navigation.NavigationPropertyConfiguration");

        var isSelfRefencingMethod = associationTypeExtensionsType.GetMethod("IsSelfReferencing", BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static);
        IsSelfReferencing = associationType => (bool)isSelfRefencingMethod.Invoke(null, new object[] { associationType });

        var isRequiredToManyMethod = associationTypeExtensionsType.GetMethod("IsRequiredToMany", BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static);
        IsRequiredToMany = associationType => (bool)isRequiredToManyMethod.Invoke(null, new object[] { associationType });

        var isManyToRequiredMethod = associationTypeExtensionsType.GetMethod("IsManyToRequired", BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static);
        IsManyToRequired = associationType => (bool)isManyToRequiredMethod.Invoke(null, new object[] { associationType });

        var getConfigurationMethod = associationTypeExtensionsType.GetMethod("GetConfiguration", BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static);
        GetConfiguration = associationType => getConfigurationMethod.Invoke(null, new object[] { associationType });

        var deleteActionProperty = navigationPropertyConfigurationType.GetProperty("DeleteAction", BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance);
        NavigationPropertyConfigurationGetDeleteAction = navProperty => (OperationAction?)deleteActionProperty.GetValue(navProperty);
    }

    public virtual void Apply(AssociationType item, DbModel model)
    {
        if (IsSelfReferencing(item))
            return;
        var propertyConfiguration = GetConfiguration(item);
        if (propertyConfiguration != null && NavigationPropertyConfigurationGetDeleteAction(propertyConfiguration).HasValue)
            return;
        AssociationEndMember collectionEndMember = null;
        AssociationEndMember singleNavigationEndMember = null;
        if (IsRequiredToMany(item))
        {
            collectionEndMember = GetSourceEnd(item);
            singleNavigationEndMember = GetTargetEnd(item);
        }
        else if (IsManyToRequired(item))
        {
            collectionEndMember = GetTargetEnd(item);
            singleNavigationEndMember = GetSourceEnd(item);
        }
        if (collectionEndMember == null || singleNavigationEndMember == null)
            return;

        var collectionCascadeDeleteAttribute = GetCascadeDeleteAttribute(collectionEndMember);
        var singleCascadeDeleteAttribute = GetCascadeDeleteAttribute(singleNavigationEndMember);

        if (collectionCascadeDeleteAttribute != null || singleCascadeDeleteAttribute != null)
            collectionEndMember.DeleteBehavior = OperationAction.Cascade;
    }

    private static AssociationEndMember GetSourceEnd(AssociationType item)
    {
        return item.KeyMembers.FirstOrDefault() as AssociationEndMember;
    }
    private static AssociationEndMember GetTargetEnd(AssociationType item)
    {
        return item.KeyMembers.ElementAtOrDefault(1) as AssociationEndMember;
    }

    private static CascadeDeleteAttribute GetCascadeDeleteAttribute(EdmMember edmMember)
    {
        var clrProperties = edmMember.MetadataProperties.FirstOrDefault(m => m.Name == "ClrPropertyInfo");
        if (clrProperties == null)
            return null;

        var property = clrProperties.Value as PropertyInfo;
        if (property == null)
            return null;

        return property.GetCustomAttribute<CascadeDeleteAttribute>();
    }
}