Finds the inverse Property of an EF 6 NavigationProperty.

EFInverseProperty.cs

using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Data.Entity.Core.Metadata.Edm;
using System.Data.Entity.Infrastructure;
using System.Reflection;

class Program
{
    static PropertyInfo GetInverseProperty(DbContext context, Type parentType, string parentProperty)
    {
        var meta = ((IObjectContextAdapter)context).ObjectContext.MetadataWorkspace;
        // Note: a CLR class can have a null Namespace (if it isn't defined in one), 
        //       but EDM throws NullArgumentException and expects an empty string instead.
        // TODO: if this code can be called from contexts where `parentType` isn't guaranteed to be 
        //       a mapped EF class, you may want to call `TryGetType` and handle the error instead.
        var oType = meta.GetType(parentType.Name, parentType.Namespace ?? "", DataSpace.OSpace) as EntityType;
        // TODO: if this code can be called from contexts where `parentProperty` isn't guaranteed to be 
        //       a mapped EF navigation property, you may want to call `TryGetValue` and handle the error instead.
        var navigation = oType.NavigationProperties.GetValue(parentProperty, ignoreCase: false);
        var cType = (AssociationType)meta.GetEdmSpaceType(navigation.RelationshipType);
        // TODO: Could it sometimes be [0] ? 
        //       Maybe it's safer to check if the property is different from the source property?
        //       Don't check the type though, as it could be a self-referencing relationship.
        var endMember = (AssociationEndMember)cType.RelationshipEndMembers[1];
        return endMember.MetadataProperties.TryGetValue("ClrPropertyInfo", ignoreCase: false, out var metaProperty)
            ? (PropertyInfo)metaProperty.Value
            : null;    // No inverse property
    }

    static void Main(string[] args)
    {
        var db = new Context();
        var foo = typeof(Foo);
        Console.WriteLine(GetInverseProperty(db, foo, nameof(Foo.Bars)));
        Console.WriteLine(GetInverseProperty(db, foo, nameof(Foo.Children)));
    }
}

// Fake data model for demonstration:

class Foo 
{
    public int Id { get; set; }
    // This one has an inverse nav
    public ICollection<Bar> Bars { get; set; }
    // This one doesn't
    public ICollection<Child> Children { get; set; }
}

class Bar
{
    public int Id { get; set; }
    public int FooId { get; set; }
    public Foo Foo { get; set; }
}

class Child 
{
    public int Id { get; set; }
    public int FooId { get; set; }
}

class Context : DbContext
{
    public DbSet<Foo> Foos { get; set; }
    public DbSet<Bar> Bars { get; set; }
    public DbSet<Child> Children { get; set; }
}