Convert nested Generic List to DataTable in C# and VB.Net

protected void Page_Load(object sender, EventArgs e)

{

    List<Employee> employees = new List<Employee>();

    List<EmployeeDepartments> departments = new List<EmployeeDepartments>();

 

    departments.Add(new EmployeeDepartments { Mark = 48, Department = "Physics" });

    departments.Add(new EmployeeDepartments { Mark = 45, Department = "Chemistry" });

    employees.Add(new Employee { Id = 1, Name = "John Hammond", EmployeeDetails = departments });

 

    departments = new List<EmployeeDepartments>();

    departments.Add(new EmployeeDepartments { Mark = 50, Department = "Mathmatics" });

    departments.Add(new EmployeeDepartments { Mark = 49, Department = "Biology" });

    employees.Add(new Employee { Id = 2, Name = "Mudassar Khan", EmployeeDetails = departments });

    gvEmployees.DataSource = CreateNestedDataTable<Employee, EmployeeDepartments>(employees, "EmployeeDetails");

    gvEmployees.DataBind();

}

 

public class Employee

{

    public int Id { get; set; }

    public string Name { get; set; }

    public List<EmployeeDepartments> EmployeeDetails { get; set; }

}

 

public class EmployeeDepartments

{

    public string Department { get; set; }

    public int Mark { get; set; }

}

 

public DataTable CreateNestedDataTable<TOuter, TInner>(IEnumerable<TOuter> list, string innerListPropertyName)

{

    PropertyInfo[] outerProperties = typeof(TOuter).GetProperties().Where(pi => pi.Name != innerListPropertyName).ToArray();

    PropertyInfo[] innerProperties = typeof(TInner).GetProperties();

    MethodInfo innerListGetter = typeof(TOuter).GetProperty(innerListPropertyName).GetGetMethod(true);

 

    DataTable table = new DataTable();

    foreach (PropertyInfo pi in outerProperties)

    {

        table.Columns.Add(pi.Name, Nullable.GetUnderlyingType(pi.PropertyType) ?? pi.PropertyType);

    }

    foreach (PropertyInfo pi in innerProperties)

    {

        table.Columns.Add(pi.Name, Nullable.GetUnderlyingType(pi.PropertyType) ?? pi.PropertyType);

    }

 

    // iterate through outer items

    foreach (TOuter outerItem in list)

    {

        var innerList = innerListGetter.Invoke(outerItem, null) as IEnumerable<TInner>;

        if (innerList == null || innerList.Count() == 0)

        {

            // outer item has no inner items

            DataRow row = table.NewRow();

            foreach (PropertyInfo pi in outerProperties)

            {

                row[pi.Name] = pi.GetValue(outerItem, null) ?? DBNull.Value;

            }

            table.Rows.Add(row);

        }

        else

        {

            // iterate through inner items

            foreach (object innerItem in innerList)

            {

                DataRow row = table.NewRow();

                foreach (PropertyInfo pi in outerProperties)

                {

                    row[pi.Name] = pi.GetValue(outerItem, null) ?? DBNull.Value;

                }

                foreach (PropertyInfo pi in innerProperties)

                {

                    row[pi.Name] = pi.GetValue(innerItem, null) ?? DBNull.Value;

                }

                table.Rows.Add(row);

            }

        }

    }

 

    return table;

}