Querying inside a Dataset C#

Question

I have an ADO.NET dataset which is set by a certain query, say

SELECT ID,USER,PRODUCT,COUNT FROM PRODUCTION

Without using a where clause I need to derive some results from the dataset. Say I want to get the User and Product count of the user who has the maximum product count. (And I want to do it by using the existing dataset. I can't derive this from dataset.)

Any idea of a way to query inside the dataset? Since there are Datatables my thought was there is some way to query it.

Answer 1

Traditional SQL queries cannot be applied to the DataSet. The following is possible, however:

• Filter rows using DataTable.Select. See here for detailed information about expressions in DataTables.
• Calculate totals etc. using DataTable.Compute.
• If these two don't do the trick, there's always LINQ.

Quick-and-dirty LINQ example: (which doesn't return a DataTable, but a list containing an anonymous type):

var joinedResult = dataTable1
  // filtering:
  .Select("MyColumn = 'value'")
  // joining tables:
  .Join(
    dataTable2.AsEnumerable(), 
    row => row.Field<long>("PrimaryKeyField"), 
    row => row.Field<long?>("ForeignKeyField"),
    // selecting a custom result:
    (row1, row2) => new { AnotherColumn = row1.Field<string>("AnotherColumn") });

AsEnumerable converts a DataTable into an IEnumerable on which LINQ queries can be performed. If you are new to LINQ, check out this introduction.

Answer 2

Yes, you can use DataTable.Select method.

DataTable table = DataSet1.Tables["Orders"];
    // Presuming the DataTable has a column named Date.
    string expression;
    expression = "Date > #1/1/00#";
    DataRow[] foundRows;

    // Use the Select method to find all rows matching the filter.
    foundRows = table.Select(expression);

    // Print column 0 of each returned row.
    for(int i = 0; i < foundRows.Length; i ++)
    {
        Console.WriteLine(foundRows[i][0]);
    }

Also see this link.

Answer 3

You can do cross-table queries of a Dataset object using LINQ to DataSet:

msdn.microsoft.com/en-us/library/bb386969.aspx