Get PropertyInfo from multiple property objects found in an Expression object - linq

Question

I need to change a function that accepts one Expression with one property inside and give it the ability to work with 2 properties at least.
I have the following base class that contains nested ElementHelper class
public class DomainObjectViewModel<TModel> where TModel : DomainObject
{
public class ElementHelper
{
public static void Create<T1>(TModel model, Expression<Func<TModel, T1>> expression)
{
var getPropertyInfo = GetPropertyInfo(expression);
//Do cool stuff
}
private static PropertyInfo GetPropertyInfo<T1>(Expression<Func<TModel, T1>> propertyExpression)
{
return (PropertyInfo)((MemberExpression)propertyExpression.Body).Member;
}
}
}
-ElementHelper class contains a Create function that gets the propertyInfo of the expression and only works if you pass one property in the expression.
Then I have the following inherited class that uses the helper function in the constructor.
public class ProductViewModel : DomainObjectViewModel<ProductEditViewModel>
{
public ProductViewModel(ProductEditViewModel model)
{
//It works for one property in the Expression
ElementHelper.Create(model, x => x.LaunchDate);
//Give the ability to pass multiple paramenters in the expression
ElementHelper.Create(model, x => new { x.LaunchDate, x.ApplyLaunchDateChanges });
}
}
I think I can use NewExpression (new { x.LaunchDate, x.ApplyLaunchDateChanges }) in order to pass it a collection of properties, but I cannot make it work.
Would you use same approach?
How you can split the passed Expression so you can get the propertyinfo of each properties found in the NewExpression object?

Answer 1

Well, since ElementHelper.GetPropertyInfo is your own method, you can decide what is allowed to pass, and then handle it appropriately inside that method.
Currently you handle only MemberExpression, so that's why it works only with single property accessor. If you want to be able to pass new { ... }, you need to add support for NewExpression like this:
private static IEnumerable<PropertyInfo> GetPropertyInfo<T1>(Expression<Func<TModel, T1>> propertyExpression)
{
var memberExpression = propertyExpression.Body as MemberExpression;
if (memberExpression != null)
return Enumerable.Repeat((PropertyInfo)memberExpression.Member, 1);
var newExpression = propertyExpression.Body as NewExpression;
if (newExpression != null)
return newExpression.Arguments.Select(item => (PropertyInfo)((MemberExpression)item).Member);
return Enumerable.Empty<PropertyInfo>(); // or throw exception
}