Linq查询-动态数据类型

Question

I have a linq query working nicely to aggregate values from a DataTable.

The idea is that a user can select one of a list of fields, and the linq aggregates data according to the field selected.

p_measure is a string variable denoting the name of a field selected.

However, in it's current form, this all only works when the selected field is of data type 'float' in the source table. If the user selects an 'int' ... then I get a cast exception thrown.

So the question is, how do i make this code 'dynamic' to handle the varying datatypes ?

// Table for receiving aggregated results 
var table = new DataTable();
table.Columns.Add(p_dimension, typeof(String));
table.Columns.Add(p_measure, typeof(Double));

// Query to perform aggregation
DataTable query = (from r in rootDT.AsEnumerable()
                   group r by new
                           {
                              Dimension = r.Field<string>(p_dimension)
                           } into g
                             select new
                           {
                              Dimension = g.Key.Dimension,
                              Measure = g.Sum(x => x.Field<double>(p_measure))
                            }
                         ).Aggregate(table, (dt, r) => dt.Rows.Add(r.Dimension,r.Measure); return dt; });

I can handle the type in the "new DataTable" declaration (line 4):

table.Columns.Add(p_measure, typeof(Double));

by generating & setting a variable of type Type, thus :

table.Columns.Add(p_measure, myTypeVariable);

But I am at a loss how to handle this one:

x.Field<double>(p_measure)

Any ideas ??

Answer 1

If you want the result to always be a double you can use

Measure = g.Sum(x => Convert.ToDouble(x[p_measure]))

Then it will only on any numeric type, or string columns whose values can all be parsed to a double .