How do I change a T4 Template to add Serializable to generated classes? - c#-4.0

Question

As the question says I would like to add [Serializable] to classes generated from a T4 Template .tt file.
As far as the information I found gave me, is that I could put using System.Runtime.Serialization; and [Serializable] as plain text in the .tt file as a "Text block". Except it won't generate these in the output files.
<#
EndNamespace(code);
}
foreach (var complex in typeMapper.GetItemsToGenerate<ComplexType>(itemCollection))
{
fileManager.StartNewFile(complex.Name + ".cs");
BeginNamespace(code);
#>
<#=codeStringGenerator.UsingDirectives(inHeader: false, includeCollections: false)#>
using System.Runtime.Serialization;
[Serializable]
<#=Accessibility.ForType(complex)#> partial class <#=code.Escape(complex)#>
{
<#
var complexProperties = typeMapper.GetComplexProperties(complex);
var propertiesWithDefaultValues = typeMapper.GetPropertiesWithDefaultValues(complex);
if (propertiesWithDefaultValues.Any() || complexProperties.Any())
T4 Template code
//------------------------------------------------------------------------------
// <auto-generated>
// This code was generated from a template.
//
// Manual changes to this file may cause unexpected behavior in your application.
// Manual changes to this file will be overwritten if the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------
namespace Projectnamespace.Models
{
using System;
using System.Collections.Generic;
public partial class Customer
{
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
Generated code
I would love to know if there is a special syntax for this or something I have to change to get this to work.
I am using Visual Studio 2019, .NET Framework 4.7.2, an MVC 5 project and an .edmx file for the database.

Answer 1

Well.. Eventually I found a way to add "using System.Runtime.Serialization;" and "[Serializable]" in every class by adding some line to the UsingDirectives method in the T4 Template.
By changing this:
public string UsingDirectives(bool inHeader, bool includeCollections = true)
{
return inHeader == string.IsNullOrEmpty(_code.VsNamespaceSuggestion())
? string.Format(
CultureInfo.InvariantCulture,
"{0}using System;{1}" +
"{2}",
inHeader ? Environment.NewLine : "",
includeCollections ? (Environment.NewLine + "using System.Collections.Generic;") : "",
inHeader ? "" : Environment.NewLine)
: "";
}
By editing the last row into this:
public string UsingDirectives(bool inHeader, bool includeCollections = true)
{
return inHeader == string.IsNullOrEmpty(_code.VsNamespaceSuggestion())
? string.Format(
CultureInfo.InvariantCulture,
"{0}using System;{1}" +
"{2}",
inHeader ? Environment.NewLine : "",
includeCollections ? (Environment.NewLine + "using System.Collections.Generic;") : "",
inHeader ? "" : Environment.NewLine + "using System.Runtime.Serialization;" + Environment.NewLine + "[Serializable]")
: "";
}