Extend ModelState to accept as parameter Expression in Razor view model

Question

I want to reduce typo issues so I need method like ModelStateFor which should accept Expression. nameof() method is not sufficient because it doesn't work correctly for nested properties.

Answer 1

I created extension for ModelState to handle that case. It also handle case when you use nested property like Input.Login.

public static ModelStateDictionary AddModelErrorFor<TProperty>( this ModelStateDictionary modelState, Expression<Func<TProperty>> expression, string errorMessage )
{
    modelState.AddModelError( expression.GetPathOfProperty(), errorMessage );
    return modelState;
}
public static string GetPathOfProperty<T>( this Expression<Func<T>> expression )
{
    var stringBuilder = new StringBuilder();
    var memberExpression = expression.Body as MemberExpression;
    while ( memberExpression != null )
    {
        if ( stringBuilder.Length > 0 )
            stringBuilder.Insert( 0, "." );
        stringBuilder.Insert( 0, memberExpression.Member.Name );
        memberExpression = memberExpression.Expression as MemberExpression;
    }
    return stringBuilder.ToString();
}

PathOfProperty method is based on this question