MVC5 T4 ModelMetadata.Properties IsNullable or IsRequired

Problem

What should happen is the ability to switch between two completely different classes

From : To :Microsoft.AspNet.Scaffolding.Core.Metadata.PropertyMetadata


System.Reflection.PropertyInfo

The class PropertyMetadata

provided by ASP.NET Scaffolding provides relatively limited data and a direct reference to the original type or attributes.

Here's a mapping of the two properties : ^{(click for full resolution)}

because honestly, why bother working with a custom model generator all this time without access to the rich world of data provided by System.Reflection

Decision

• We're going to create a T4 helper method right inside our regular web assembly. This is just a method static
  
  that can be used externally. We'll register it later inside the T4 file so it can actually be used.

  So add a file like this anywhere in your project:

  UtilityTools.cs
  
  

  using System;
  using System.Reflection;
  using System.ComponentModel.DataAnnotations;
  namespace UtilityTools
  {
      public static class T4Helpers
      {
          public static bool IsRequired(string viewDataTypeName, string propertyName)
          {
              bool isRequired = false;
  
              Type typeModel = Type.GetType(viewDataTypeName);
              if (typeModel != null)
              {
                  PropertyInfo pi = typeModel.GetProperty(propertyName);
                  Attribute attr = pi.GetCustomAttribute<RequiredAttribute>();
                  isRequired = attr != null;
              }
  
              return isRequired;
          }
      }
  }
  
        
  
          
          
          
        
  
      

• Now register it by adding your assembly to the `Imports.include.t4 file :

  <#@ assembly name="C:\stash\cshn\App\MyProj\bin\MyProj.dll" #>
  
        
  
          
          
          
        
  
      

  

  At the same time, when other assemblies are loaded, it actually gives us access to any static methods inside any assembly we loaded, giving minimal access to UtilityTools.T4Helpers.IsRequired
  
  

• Make sure you rebuild your app (and maybe restart Visual Studio)

• We can now use this inside any of our T4 templates, like this:

  <#= UtilityTools.T4Helpers.IsRequired(ViewDataTypeName, property.PropertyName) #>
  
        
  
          
          
          
        
  
      

  

Further reading :

The above solution is heavily adapted from the following articles and questions:

• MVC 5 T4 Templates and Model Property Attributes
• MVC 4 user data annotations read in T4 footer
• Get a scaffolder to create fields in a specific order

Council . Debugging T4 templates can sometimes be a bear, so I wrote this test template that helps in dumping information from the model so that you can easily evaluate what ASP.NET uses as values ​​for Hydration PropertyMetadata

Gist : https://gist.github.com/ KyleMit / fc9ccfbc2af03462d660257103326509

Note : Type.GetType("Namespace.Qualified.TypeName")

Works only when the type is found in the mscorlib.dll file or in the currently executing assembly . If your model is part of a business library, you either need to use like this :AssemblyQualifiedName

Type.GetType("Namespace.Qualified.TypeName,DllName")
      

        
        
        
      

    

or you can search for all currently running assemblies such as:

public static Type GetType(string typeName)
{
    var type = Type.GetType(typeName);
    if (type != null) return type;
    foreach (var a in AppDomain.CurrentDomain.GetAssemblies())
    {
        type = a.GetType(typeName);
        if (type != null)
            return type;
    }
    return null;
}

      

        
        
        
      

    

for this to work, you will need to add any business libraries that contain classes to the list of imported assemblies (same as we did earlier in the imports.t4 file):

<#@ assembly name="C:\stash\cshn\App\MyProj\bin\MyProj.Business.dll" #>