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

Hi yogesjoshi,

Refer below sample.

HTML

<asp:GridView runat="server" ID="gvEmployees" />

Namespaces

C#

using System.Data;
using System.Reflection;

VB.Net

Imports System.Data
Imports System.Reflection

Code

C#

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;
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    Dim employees As List(Of Employee) = New List(Of Employee)()
    Dim departments As List(Of EmployeeDepartments) = New List(Of EmployeeDepartments)()
    departments.Add(New EmployeeDepartments With {
        .Mark = 48,
        .Department = "Physics"
    })
    departments.Add(New EmployeeDepartments With {
        .Mark = 45,
        .Department = "Chemistry"
    })
    employees.Add(New Employee With {
        .Id = 1,
        .Name = "John Hammond",
        .EmployeeDetails = departments
    })
    departments = New List(Of EmployeeDepartments)()
    departments.Add(New EmployeeDepartments With {
        .Mark = 50,
        .Department = "Mathmatics"
    })
    departments.Add(New EmployeeDepartments With {
        .Mark = 49,
        .Department = "Biology"
    })
    employees.Add(New Employee With {
        .Id = 2,
        .Name = "Mudassar Khan",
        .EmployeeDetails = departments
    })
    gvEmployees.DataSource = CreateNestedDataTable(Of Employee, EmployeeDepartments)(employees, "EmployeeDetails")
    gvEmployees.DataBind()
End Sub

Public Class Employee
    Public Property Id As Integer
    Public Property Name As String
    Public Property EmployeeDetails As List(Of EmployeeDepartments)
End Class

Public Class EmployeeDepartments
    Public Property Department As String
    Public Property Mark As Integer
End Class

Public Function CreateNestedDataTable(Of TOuter, TInner)(ByVal list As IEnumerable(Of TOuter), ByVal innerListPropertyName As String) As DataTable
    Dim outerProperties As PropertyInfo() = GetType(TOuter).GetProperties().Where(Function(pi) pi.Name <> innerListPropertyName).ToArray()
    Dim innerProperties As PropertyInfo() = GetType(TInner).GetProperties()
    Dim innerListGetter As MethodInfo = GetType(TOuter).GetProperty(innerListPropertyName).GetGetMethod(True)
    Dim table As DataTable = New DataTable()

    For Each pi As PropertyInfo In outerProperties
        table.Columns.Add(pi.Name, If(Nullable.GetUnderlyingType(pi.PropertyType), pi.PropertyType))
    Next

    For Each pi As PropertyInfo In innerProperties
        table.Columns.Add(pi.Name, If(Nullable.GetUnderlyingType(pi.PropertyType), pi.PropertyType))
    Next

    For Each outerItem As TOuter In list
        Dim innerList = TryCast(innerListGetter.Invoke(outerItem, Nothing), IEnumerable(Of TInner))

        If innerList Is Nothing OrElse innerList.Count() = 0 Then
            Dim row As DataRow = table.NewRow()

            For Each pi As PropertyInfo In outerProperties
                row(pi.Name) = If(pi.GetValue(outerItem, Nothing), DBNull.Value)
            Next

            table.Rows.Add(row)
        Else

            For Each innerItem As Object In innerList
                Dim row As DataRow = table.NewRow()

                For Each pi As PropertyInfo In outerProperties
                    row(pi.Name) = If(pi.GetValue(outerItem, Nothing), DBNull.Value)
                Next

                For Each pi As PropertyInfo In innerProperties
                    row(pi.Name) = If(pi.GetValue(innerItem, Nothing), DBNull.Value)
                Next

                table.Rows.Add(row)
            Next
        End If
    Next

    Return table
End Function

Screenshot