DataRow DataTable DataTable foreach Extension Generic

`DataRow` Field

The Field method on DataRow accesses a field. It is an extension method. It is found in the System.Data namespace.

Notes, method

Field() is a generic method—this means it returns typed data. It makes field access easier. We can avoid complicated casting expressions and exception handling.

Example

DataTable can be enumerated with the foreach-loop. Accessing the fields themselves is somewhat more complicated. The fields can have different types.

Note The DataTable in the example has cells with types of int, string and DateTime.

Start The example uses the foreach-loop. In the statement list it assigns variables to the results of the Field extension method.

Tip The Field extension method receives a type parameter. It has several parameter list overloads.

Detail The weight, name, code, and date variables are assigned to the results of the Field method with different parameters.

using System;
using System.Data;

class Program
{
    static void Main()
    {
        //
        // Loop over DataTable rows and call the Field extension method.
        //
        foreach (DataRow row in GetTable().Rows)
        {
            // Get first field by column index.
            int weight = row.Field<int>(0);

            // Get second field by column name.
            string name = row.Field<string>("Name");

            // Get third field by column index.
            string code = row.Field<string>(2);

            // Get fourth field by column name.
            DateTime date = row.Field<DateTime>("Date");

            // Display the fields.
            Console.WriteLine("{0} {1} {2} {3}", weight, name, code, date);
        }
    }

    static DataTable GetTable()
    {
        DataTable table = new DataTable(); // Create DataTable
        table.Columns.Add("Weight", typeof(int)); // Add four columns
        table.Columns.Add("Name", typeof(string));
        table.Columns.Add("Code", typeof(string));
        table.Columns.Add("Date", typeof(DateTime));
        table.Rows.Add(57, "Koko", "A", DateTime.Now); // Add five rows
        table.Rows.Add(130, "Fido", "B", DateTime.Now);
        table.Rows.Add(92, "Alex", "C", DateTime.Now);
        table.Rows.Add(25, "Charles", "D", DateTime.Now);
        table.Rows.Add(7, "Candy", "E", DateTime.Now);
        return table;
    }
}57 Koko A 7/14/2009 6:20:48 AM
130 Fido B 7/14/2009 6:20:48 AM
92 Alex C 7/14/2009 6:20:48 AM
25 Charles D 7/14/2009 6:20:48 AM
7 Candy E 7/14/2009 6:20:48 AM

Parameters

There are 2 parameter lists on each method invocation to Field. The first parameter to the method is enclosed in the brackets. This is called a type parameter.

Tip A type parameter indicates what type (such as int or string) you want the method to cast the result to.

Note The second parameter list indicates the name or location of the field by its column identifier.

Internals

How does Field() work internally? The DataRowExtensions class is an extension method class located in the System.Data.DataSetExtensions.dll file.

And When you use the methods such as Field in this class, the metadata loader will store this additional DLL in memory.

Info Field() will internally invoke a generic method that validates the parameter. It then uses a generic method to unbox the object.

Summary