getting the values from a nested complex object that is passed to a partial view

Question

You can pass the prefix to the partial using

@Html.Partial("MyPartialView", Model.ComplexModel, 
    new ViewDataDictionary { TemplateInfo = new TemplateInfo { HtmlFieldPrefix = "ComplexModel" }})

which will perpend the prefix to you controls name attribute so that <input name="Name" ../> will become <input name="ComplexModel.Name" ../> and correctly bind to typeof MyViewModel on post back

Edit

To make it a little easier, you can encapsulate this in a html helper

public static MvcHtmlString PartialFor<TModel, TProperty>(this HtmlHelper<TModel> helper, Expression<Func<TModel, TProperty>> expression, string partialViewName)
{
  string name = ExpressionHelper.GetExpressionText(expression);
  object model = ModelMetadata.FromLambdaExpression(expression, helper.ViewData).Model;
  var viewData = new ViewDataDictionary(helper.ViewData)
  {
    TemplateInfo = new System.Web.Mvc.TemplateInfo 
    { 
      HtmlFieldPrefix = string.IsNullOrEmpty(helper.ViewData.TemplateInfo.HtmlFieldPrefix) ? 
        name : $"{helper.ViewData.TemplateInfo.HtmlFieldPrefix}.{name}"
    }
  };
  return helper.Partial(partialViewName, model, viewData);
}

and use it as

@Html.PartialFor(m => m.ComplexModel, "MyPartialView")

If you use tag helpers, the partial tag helper accepts a for attribute, which does what you expect.

<partial name="MyPartialView" for="ComplexModel" />

Using the for attribute, rather than the typical model attribute, will cause all of the form fields within the partial to be named with the ComplexModel. prefix.

You can try passing the ViewModel to the partial.

@model my.path.to.namespace.MyViewModel
@Html.TextBoxFor(m => m.ComplexModel.Name)

Edit

You can create a base model and push the complex model in there and pass the based model to the partial.

public class MyViewModel :BaseModel
{
    public string SomeProperty { get; set; }
}

 public class MyViewModel2 :BaseModel
{
    public string SomeProperty2 { get; set; }
}

public class BaseModel
{
    public MyComplexModel ComplexModel { get; set; }
}
public class MyComplexModel
{
    public int id { get; set; }
    public string Name { get; set; }
    ...
}

Then your partial will be like below :

@model my.path.to.namespace.BaseModel
@Html.TextBoxFor(m => m.ComplexModel.Name)

If this is not an acceptable solution, you may have to think in terms of overriding the model binder. You can read about that here.