C# Expression - Getdefault Value or convert int? to int

Question

I have a Class like below

public class GrouppedStockGift
{
    public DateTime? TimeCreated { get; set; }
    public int? StoreID { get; set; }
    public int? UserCreated { get; set; }
    public int? WorksID { get; set; }
    public int? WorkOrderCode { get; set; }
    public decimal? GiftPrice { get; set; }
    public decimal? GiftMoney { get; set; }
    public int SaleCount { get; set; }
}

I have Create a dynamic expression builder, in some case i need to convert int? to int or getdefaultvalue of int for example

var sumMethodint = typeof(Enumerable).GetMethods()
                       .Single(x => x.Name == "Sum"
                                 && x.GetParameters().Count() == 2
                                 && x.GetParameters()[1]
                                     .ParameterType
                                     .GetGenericArguments()[1] == typeof(int?));
sumMethodint = sumMethodint.MakeGenericMethod(typeof(GrouppedStockGift));
Expression<Func<GrouppedStockGift, int?>> SaleCount = y => y.SaleCount;
var SaleCountExtractor = Expression.Call(sumMethodint, parameter, SaleCount);
bindings.Add(
              Expression.Bind(
                           typeof(GrouppedStockGift).GetProperty("SaleCount"),
                           SaleCountExtractor));

but when execute last row Exception returned around type mismached
because SaleCount is int but sum method return int?
can any one help me?

Ok, the problem in your binding? You should show the exact exception with stack trace if it possible for better assistance. — Hamlet Hakobyan, Oct 12 '14 at 10:06

Mehdi Haghshenas · Accepted Answer · 2014-10-12T09:58:11.443

0

You must just change Expression.Call row to

var SaleCountExtractor = Expression.Call(Expression.Call(sumMethodint, parameter, SaleCount), "GetValueOrDefault", Type.EmptyTypes);

in the above code

Expression.Call(exp, "GetValueOrDefault", Type.EmptyTypes);

get default value of int

edited Oct 12 '14 at 09:58

answered Oct 12 '14 at 09:44

Mehdi Haghshenas

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score 0 · Answer 2 · answered Oct 12 '14 at 10:23

I assume that problem is in your decision to use the overload of Sum which returns int?. You should use the another overload which gets selecotr of type Func<T, int> and returns int.

var parameter = Expression.Parameter(typeof (IEnumerable<GrouppedStockGift>));
var sumMethodint = typeof(Enumerable).GetMethods()
            .Single(x => x.Name == "Sum"
                        && x.GetParameters().Count() == 2
                        && x.GetParameters()[1]
                            .ParameterType
                            .GetGenericArguments()[1] == typeof(int));
sumMethodint = sumMethodint.MakeGenericMethod(typeof(GrouppedStockGift));
Expression<Func<GrouppedStockGift, int>> saleCount = y => y.SaleCount;
var saleCountExtractor = Expression.Call(sumMethodint, parameter, saleCount);

bindings.Add(Expression.Bind(typeof(GrouppedStockGift).GetProperty("SaleCount"),
                             saleCountExtractor));

C# Expression - Getdefault Value or convert int? to int

2 Answers2