LINQ Query to DataTable.DataSource

问题

I am trying to perform a LINQ query on a DataTable and show the result in another DataTable. My source DataTable looks something like this:

DataTable myDataTable = new DataTable();
myDataTable.Columns.Add("OrderID", typeof(int));
myDataTable.Columns.Add("Date", typeof(DateTime));
myDataTable.Columns.Add("UnitsPurchased", typeof(int));

The resulting DataTable looks like this when filled:

Order ID   Date    Units Purchased  
16548    10/15/09      250  
17984    11/03/09      512   
20349    01/11/10      213  
34872    01/15/10      175

My current LINQ query looks like this:

IEnumerable<DataRow> query = (from row in myDataTable.AsEnumerable()
                              where row.UnitsPurchased > 200
                              select new
                              {
                                 row.OrderID,
                                 row.Date,
                                 row.UnitsPurchased
                              }) as IEnumerable<DataRow>;

resultDataTable.DataSource = query.CopyToDataTable<DataRow>();

Every time I run this code query is null. I can see that that the as IEnumerable<DataRow> is the culprit, but it makes no since to me since DataTable.AsEnumerable() returns an IEnumerable<DataRow>. Any help would be appreciated.

回答1:

When you select new { }, you're actually getting an IEnumerable<(Anonymous Type)>, not IEnumerable<DataRow>. So your as IEnumerable<DataRow> will return null, since it can't be directly cast.

Either select new MyDataRow(constructor using values...) or something, or just do var query =... without the as cast. There's an msdn article about using CopyToDataTable with a non-DataRow generic parameter, though I haven't read it in depth, but selecting new DataRows is probably the easier solution.

回答2:

Why do you have to create a new Anonymous Type. When you can simply do this .



DataTable myDataTable = new DataTable();
            myDataTable.Columns.Add("OrderID", typeof(int));
            myDataTable.Columns.Add("Date", typeof(DateTime));
            myDataTable.Columns.Add("UnitsPurchased", typeof(int));

        var datarow1 = myDataTable.NewRow();
        datarow1.SetField("OrderID", 16548);
        datarow1.SetField("Date", DateTime.Parse("10/10/09"));
        datarow1.SetField("UnitsPurchased", 250);

        var datarow2 = myDataTable.NewRow();
        datarow2.SetField("OrderID", 17984);
        datarow2.SetField("Date", DateTime.Parse("11/03/09"));
        datarow2.SetField("UnitsPurchased", 512);

        var datarow3 = myDataTable.NewRow();
        datarow3.SetField("OrderID", 20349);
        datarow3.SetField("Date", DateTime.Parse("01/11/10"));
        datarow3.SetField("UnitsPurchased", 213);

        var datarow4 = myDataTable.NewRow();
        datarow4.SetField("OrderID", 34872);
        datarow4.SetField("Date", DateTime.Parse("10/01/10"));
        datarow4.SetField("UnitsPurchased", 175);


        myDataTable.Rows.Add(datarow1);
        myDataTable.Rows.Add(datarow2);
        myDataTable.Rows.Add(datarow3);
        myDataTable.Rows.Add(datarow4);

        var filteredTable = myDataTable.AsEnumerable().OfType<DataRow>().Where(row => row.Field<int>("UnitsPurchased") > 200).Select(r => r);

        resultDataTable.DataSource = filteredTable.CopyToDataTable();

来源：https://stackoverflow.com/questions/2502850/linq-query-to-datatable-datasource

标签

linq

datasource