Linq.Dynamic Select custom column with operation-CodePudding

I use LINQ Dynamic Query Library https://weblogs.asp.net/scottgu/dynamic-linq-part-1-using-the-linq-dynamic-query-library It works great for querying to query fields optionally

  IQueryable GetSource( DataTable t, String str)
        {
    //Working str = "new (T[\"ss\"] as ss,T[\"xx\"] as xx )"
   //Not Working str = "new (T[\"ss\"] as ss, T[\"xx\"] as xx , T[\"ss\"]  T[\"xx\"] as yy)"
           return (from T in t.AsEnumerable()
                   select new{T}).AsQueryable().Select(str);  
        }

But when I try to Operations such as (addition - multiplication - division - merge) gets wrong How can I do the accounting operations and merge fields

CodePudding user response：

You are using the DataRow item property to get the value for a field. This method returns an object which you can't add. You need to cast to the proper type.

"new (T[\"ss\"] as ss, T[\"xx\"] as xx, int(T[\"ss\"]) int(T[\"xx\"]) as yy)"

CodePudding user response：

Thanks Indeed, it must be converted because it is the object

 IQueryable GetSource( DataTable t, String str)
        {
    //Working str = "new (T[\"ss\"] as ss,T[\"xx\"] as xx )"
   //Working str = "new (T[\"ss\"] as ss,T[\"xx\"] as xx , string.Concat(T[\"ss\"], T[\"xx\"])  as yy  )"
  //Working str = ""new (T[\"ss\"] as ss,T[\"xx\"] as xx , decimal(T[\"ss\"])   decimal(T[\"xx\"])  as yy  )""

           return (from T in t.AsEnumerable()
                   select new{T}).AsQueryable().Select(str);  
        }