Reference a scalar property from a string value - wpf

Question

I have a combobox that contains a list of scalar properties of an entity. I need to do a search on the property specified by the user in the combobox.
How do I reference the property when I have it as a string?
Something similar to DBSet<> for entity.
Example:
if (order.Firstname != null && order.Firstname.ToLower().Contains(textBoxSearch.Text.ToLower()))
In the above example, I need to replace Firstname with Surname or any other property, at runtime, depending on what the user selected.

Answer 1

You can always use reflection, for your case you'll need something along these lines:
static void Main(string[] args)
{
var entity = new Entity {
Height = 172,
FirstName = "Foo",
Birthday = new DateTime(1, 1, 1995)
};
var firstName = GetEntityProperty<string>(entity, "FirstName");
}
public static T GetEntityProperty<T>(object entity, string propertyName)
{
var type = entity.GetType();
var property = type.GetProperty(propertyName);
return (T)property.GetValue(entity);
}

Answer 2

Provided solution works, but it is not strongly-typed, so it is sensible to property renaming. A strongly-typed approach can be used, but it requires some setup. However, part of the setup is so generic that it can be reused:
public class Order
{
public String OrderNo { get; set; }
public String FirstName { get; set; }
public String LastName { get; set; }
public String Misc { get; set; }
}
// clearly define properties that allow search
public enum OrderSearchableProp
{
OrderNo = 1,
FirstName = 2,
LastName = 3
}
class Program
{
// strongly-type requires an explicit mapping between property and its expression within the order object
static Dictionary<OrderSearchableProp, Expression<Func<Order, String>>> OrderSearchableMap = new Dictionary<OrderSearchableProp, Expression<Func<Order, string>>>()
{
{ OrderSearchableProp.OrderNo, o => o.OrderNo },
{ OrderSearchableProp.FirstName, o => o.FirstName },
{ OrderSearchableProp.LastName, o => o.LastName },
};
// this gets a PropertyInfo based from an Expression. It should be placed into a generic utility class
// credit goes to Daniel - http://stackoverflow.com/a/17116267/2780791
public static PropertyInfo GetPropertyFromExpression<T, TProp>(Expression<Func<T, TProp>> GetPropertyLambda)
{
MemberExpression Exp = null;
//this line is necessary, because sometimes the expression comes in as Convert(originalexpression)
if (GetPropertyLambda.Body is UnaryExpression)
{
var UnExp = (UnaryExpression)GetPropertyLambda.Body;
if (UnExp.Operand is MemberExpression)
{
Exp = (MemberExpression)UnExp.Operand;
}
else
throw new ArgumentException();
}
else if (GetPropertyLambda.Body is MemberExpression)
{
Exp = (MemberExpression)GetPropertyLambda.Body;
}
else
{
throw new ArgumentException();
}
return (PropertyInfo)Exp.Member;
}
public static IList<Order> getFilteredOrders(int propFilterValue, IList<Order> orders, String needle)
{
var filterValue = (OrderSearchableProp)propFilterValue;
var filterProp = OrderSearchableMap[filterValue];
var lowNeedle = needle?.ToLower() ?? String.Empty;
return orders.Where(o =>
{
var propInfo = GetPropertyFromExpression<Order, String>(filterProp);
var propValue = (String) propInfo.GetValue(o) ?? String.Empty;
return propValue.ToLower().Contains(lowNeedle);
}).ToList();
}
static void Main(string[] args)
{
// can be used to populate the combo items
// otherwise, not used in this example
OrderSearchableProp[] enumValues = (OrderSearchableProp[])Enum.GetValues(typeof(OrderSearchableProp));
// test orders
var orderList = new List<Order>()
{
new Order() { OrderNo = "1234ABC", FirstName = "George", LastName = "Taylor", Misc = "Extra information"},
new Order() { OrderNo = "AB10", FirstName = "Anonymous", LastName = "X", Misc = "No comment"}
};
// test OrderNo search
var searchProp = (int) OrderSearchableProp.OrderNo;
var foundOrders = getFilteredOrders(searchProp, orderList, "ABC");
// test FirstName search
searchProp = (int)OrderSearchableProp.FirstName;
foundOrders = getFilteredOrders(searchProp, orderList, "a");
// test LastName search with empty string
searchProp = (int)OrderSearchableProp.LastName;
foundOrders = getFilteredOrders(searchProp, orderList, "");
// empty return
searchProp = (int)OrderSearchableProp.OrderNo;
foundOrders = getFilteredOrders(searchProp, orderList, null);
}
}