How to dynamically create a Lambda expression that contains dot notation

Question

I have a method today that works that returns a lambda expression based on a string property name, i.e. I pass in "Description" and it return a lambda of d => d.Description. This works great, but now I need to return a lambda expression given a string that contains a dot notation, i.e. I want to passing "Customer.Name" and get a lambda expression back of d => d.Customer.Name. Below is the method that I have already created that returns the 1 level lambda, but I'm not sure how to change it to the multi level.

protected dynamic CreateOrderByExpression(string sortColumn)
{
    var type = typeof (TEntity);
    Type entityType = null;
    if (type.IsInterface)
    {
        var propertyInfos = new List<PropertyInfo>();

        var considered = new List<Type>();
        var queue = new Queue<Type>();
        considered.Add(type);
        queue.Enqueue(type);
        while (queue.Count > 0)
        {
            var subType = queue.Dequeue();
            foreach (var subInterface in subType.GetInterfaces().Where(subInterface => !considered.Contains(subInterface)))
            {
                considered.Add(subInterface);
                queue.Enqueue(subInterface);
            }

            var typeProperties = subType.GetProperties(
                BindingFlags.FlattenHierarchy
                | BindingFlags.Public
                | BindingFlags.Instance);

            var newPropertyInfos = typeProperties
                .Where(x => !propertyInfos.Contains(x));

            propertyInfos.InsertRange(0, newPropertyInfos);

            if (propertyInfos.All(f => f.Name != sortColumn)) continue;

            entityType = subType;
            break;
        }
    }


    if (entityType == null)
    {
        return null;
    }

    var parameter = Expression.Parameter(typeof (TEntity));
    var memberExpression = Expression.Property(parameter, entityType, sortColumn);
    var lambdaExpression = Expression.Lambda(memberExpression, parameter);

    return lambdaExpression;
}

Answer 1

Create a helper method like this (to be used in the bottom part of your code):

LambdaExpression GetLambdaExpression(Type type, IEnumerable<string> properties)
{
  Type t = type;
  ParameterExpression parameter = Expression.Parameter(t);
  Expression expression = parameter;

  for (int i = 0; i < properties.Count(); i++)
  {
    expression = Expression.Property(expression, t, properties.ElementAt(i));
    t = expression.Type;
  }

  var lambdaExpression = Expression.Lambda(expression, parameter);
  return lambdaExpression;
}

Now use it like this:

GetLambdaExpression(typeof(Outer), new[] { "InnerProperty", "MyProperty" });

For the following classes:

class Outer
{
    public Inner InnerProperty { get; set; }
}

class Inner
{
    public int MyProperty { get; set; }
}

I know it could have been a little more suited to your original code but I guess you can go from here (like converting the string with dots into an array). And I know it could have been done using recursion but I got a headache today...