不能使用匿名类型的sum

Question

I can't use Sum() function in LINQ.

var results = _resultTable.AsEnumerable()
           .Select(x => new
            {
                AccountId = x["AccountID"],
                SubAccountId = x["SubAccount"],
                Amount = x["Amount"]
            })
            .GroupBy(s => new { s.AccountId, s.SubAccountId })
            .Select(x => new
            {
                x.Key.AccountId,
                x.Key.SubAccountId,
                TotalAmount = x.Sum(g => g.Amount)
            });

I can't compile code it gives errors

Cannot implicitly convert type 'object' to 'long?'. An explicit conversion exists (are you missing a cast?)

And

Cannot convert lambda expression to intended delegate type because some of the return types in the block are not implicitly convertible to the delegate return type

Answer 1

I think that's Linq-To-DataTable and you are not casting the objects to the correct type. You can't Sum objects. So you need something like this(note the DataRow.Field<int>(..) ):

.Select(x => new
        {
            AccountId = x["AccountID"],     // you should also cast
            SubAccountId = x["SubAccount"], // you should also cast
            Amount = x.Field<int>("Amount") // int you can sum, Object not
        })
        // rest

You could also cast at the end, but i don't like to fix a mess afterwards, better prevent it:

// ...
.Select(grp => new
        {
            grp.Key.AccountId,
            grp.Key.SubAccountId,
            TotalAmount = grp.Sum(x => (int)x.Amount)
        });