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Interface based model binding to populate properties value automatically

Interface is great way to make consistency and re-useability of codes. In this tutorial, I am going to show the power of interface to populate view/domain models automatically and interchange values between models.

Technologies or techniques used in this approach:
- MVC.
- Interface for models.
- MVC model binder for associated model with interface. Through this model binder we will populate values.
- T4 template to generate code to register model binder with all models associated with interface.
- Generic extension method to interchange values.

It might sounding bit complex to achieve small thing. Just hold on with me and see unfolding. This will result in easier maintenance and less repetitive code.

First let's start with creation of Interface that need to be populate automatically. This interface would be implemented on models and values will be auto-populated on binder.

   /// <summary>  
   /// Interface for storing entry related values  
   /// </summary>  
   public interface IAddUpdate  
   {  
     /// <summary>  
     /// Gets or sets the created at.  
     /// </summary>  
     /// <value>The created at.</value>  
     DateTime CreatedAt { get; set; }  
     /// <summary>  
     /// Gets or sets the created by.  
     /// </summary>  
     /// <value>The created by.</value>  
     string CreatedBy { get; set; }  
     /// <summary>  
     /// Gets or sets the updated at.  
     /// </summary>  
     /// <value>The updated at.</value>  
     DateTime? UpdatedAt { get; set; }  
     /// <summary>  
     /// Gets or sets the updated by.  
     /// </summary>  
     /// <value>The updated by.</value>  
     string UpdatedBy { get; set; }  
   }  

After creation of interface we can create our domain and view models by inheriting above interface.

You can have any properties or functionality in the domain model. Just that above interface need to be implemented.

  /// <summary>  
   /// User domain model  
   /// </summary>  
   public class UserModel  
     : IAddUpdate  
   {  
     /// <summary>  
     /// Gets or sets the identifier.  
     /// </summary>  
     /// <value>  
     /// The identifier.  
     /// </value>  
     public int Id { get; set; }  
     /// <summary>  
     /// Gets or sets the user identifier.  
     /// </summary>  
     /// <value>  
     /// The user identifier.  
     /// </value>  
     public string UserId { get; set; }  
     /// <summary>  
     /// Gets or sets the email.  
     /// </summary>  
     /// <value>  
     /// The email.  
     /// </value>  
     public string Email { get; set; }  
     /// <summary>  
     /// Gets or sets the password.  
     /// </summary>  
     /// <value>  
     /// The password.  
     /// </value>  
     public string Password { get; set; }  
     #region " IAddUpdate implementation "  
     /// <summary>  
     /// Gets or sets the created at.  
     /// </summary>  
     /// <value>  
     /// The created at.  
     /// </value>  
     public System.DateTime CreatedAt { get; set; }  
     /// <summary>  
     /// Gets or sets the created by.  
     /// </summary>  
     /// <value>  
     /// The created by.  
     /// </value>  
     public string CreatedBy { get; set; }  
     /// <summary>  
     /// Gets or sets the updated at.  
     /// </summary>  
     /// <value>  
     /// The updated at.  
     /// </value>  
     public System.DateTime? UpdatedAt { get; set; }  
     /// <summary>  
     /// Gets or sets the updated by.  
     /// </summary>  
     /// <value>  
     /// The updated by.  
     /// </value>  
     public string UpdatedBy { get; set; }  
     #endregion " IAddUpdate implementation "  
   }  

View Model creation is in similar way, interface need to be implemented. I have created constructor to initialize default value of created date as current date.

  /// <summary>  
   /// User view model  
   /// </summary>  
   public class UserViewModel  
     : IAddUpdate  
   {  
     /// <summary>  
     /// Initializes a new instance of the <see cref="UserViewModel"/> class.  
     /// </summary>  
     public UserViewModel()  
     {  
       CreatedAt = DateTime.Now;  
     }  
     /// <summary>  
     /// Gets or sets the user identifier.  
     /// </summary>  
     /// <value>  
     /// The user identifier.  
     /// </value>  
     [StringLength(15)]  
     [Required]  
     public string UserId { get; set; }  
     /// <summary>  
     /// Gets or sets the first name.  
     /// </summary>  
     /// <value>  
     /// The first name.  
     /// </value>  
     public string FirstName { get; set; }  
     /// <summary>  
     /// Gets or sets the last name.  
     /// </summary>  
     /// <value>  
     /// The last name.  
     /// </value>  
     public string LastName { get; set; }  
     /// <summary>  
     /// Gets or sets the email.  
     /// </summary>  
     /// <value>  
     /// The email.  
     /// </value>  
     [DataType(DataType.EmailAddress)]  
     public string Email { get; set; }  
     #region " IAddUpdate implementation "  
     /// <summary>  
     /// Gets or sets the created at.  
     /// </summary>  
     /// <value>  
     /// The created at.  
     /// </value>  
     public System.DateTime CreatedAt { get; set; }  
     /// <summary>  
     /// Gets or sets the created by.  
     /// </summary>  
     /// <value>  
     /// The created by.  
     /// </value>  
     public string CreatedBy { get; set; }  
     /// <summary>  
     /// Gets or sets the updated at.  
     /// </summary>  
     /// <value>  
     /// The updated at.  
     /// </value>  
     public System.DateTime? UpdatedAt { get; set; }  
     /// <summary>  
     /// Gets or sets the updated by.  
     /// </summary>  
     /// <value>  
     /// The updated by.  
     /// </value>  
     public string UpdatedBy { get; set; }  
     #endregion " IAddUpdate implementation "  
   }  

Now interface and different model creation is done. Let's look into creation of model binder which will set properties value based on IAddUpdate interface.

  /// <summary>  
   /// Model binding for IAddUpdate interface implemented models  
   /// </summary>  
   public class InterfaceIAddUpdateModelBinder  
     : DefaultModelBinder  
   {  
     /// <summary>  
     /// The Min allowed date  
     /// </summary>  
     private const int MIN_ALLOWED_YEAR = 1800;  
     /// <summary>  
     /// Binds the model by using the specified controller context and binding context.  
     /// </summary>  
     /// <param name="controllerContext">The context within which the controller operates.  
     /// The context information includes the controller, HTTP content, request context, and route data.</param>  
     /// <param name="bindingContext">The context within which the model is bound. The context includes information  
     /// such as the model object, model name, model type, property filter, and value provider.</param>  
     /// <returns>  
     /// The bound object.  
     /// </returns>  
     /// <exception cref="System.ArgumentNullException">  
     /// controllerContext  
     /// or  
     /// bindingContext  
     /// </exception>  
     public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)  
     {  
       #region " Null checks "  
       if (controllerContext == null)  
       {  
         throw new ArgumentNullException("controllerContext");  
       }  
       if (bindingContext == null)  
       {  
         throw new ArgumentNullException("bindingContext");  
       }  
       if (bindingContext.Model != null)  
       {  
         return bindingContext.Model;  
       }  
       #endregion " Null checks "  
       var model = base.BindModel(controllerContext, bindingContext);  
       var addUpdateModel = model as IAddUpdate;  
       if (addUpdateModel == null)  
       {  
         return model;  
       }  
       // Anonymous function to set values  
       // NOTE: No checks are done as it is expecting same values through interfaces.  
       Action<string, object> setPropertyValue = (propertyName, value) =>  
       {  
         var prop = bindingContext.ModelType.GetProperty(propertyName);  
         prop.SetValue(model, value, null);  
       };  
       // NOTE: Change assignment of values according to your need  
       #region " Set values "  
       if (addUpdateModel.CreatedAt.Year < MIN_ALLOWED_YEAR)  
       {  
         setPropertyValue("CreatedAt", DateTime.Now);  
       }  
       if (String.IsNullOrEmpty(addUpdateModel.CreatedBy))  
       {  
         setPropertyValue("CreatedBy", controllerContext.RequestContext.HttpContext.User.Identity.Name);  
       }  
       if (!addUpdateModel.UpdatedAt.HasValue)  
       {  
         setPropertyValue("UpdatedAt", DateTime.Now);  
       }  
       if (String.IsNullOrEmpty(addUpdateModel.UpdatedBy))  
       {  
         setPropertyValue("UpdatedBy", controllerContext.RequestContext.HttpContext.User.Identity.Name);  
       }  
       #endregion " Set values "  
       return model;  
     }  
   }  

The above model binder will try to check if model is using interface. If model is using IAddUpdate interface then it would populate values according to user identity/principal. These could be customized according to your need.

Our interface, model and binder is set now. Now we need to create T4 template to generate code to register models with InterfaceIAddUpdateModelBinder binder. This will take care of any new models getting associated with IAddUpdate interface.

 // TODO: Change path according to project/folder structure  
 <#@ assembly name="$(SolutionDir)ModelInterface\bin\ModelInterface.Model.dll" #><#@ template debug="true" hostSpecific="true" #>  
 <#@ template language="C#" debug="false" hostspecific="true" #>  
 <#@ output extension=".cs" #>  
 <#@ import namespace="System" #>  
 <#@ import namespace="System.Linq" #>  
 <#@ import namespace="System.Collections" #>  
 <#@ import namespace="System.Reflection" #>  
 <#@ import namespace="System.Collections.Generic" #>   
 <#@ include file="EF.Utility.CS.ttinclude"#>  
 <#  
      CodeGenerationTools code = new CodeGenerationTools(this);  
      // Interface to look for  
      var interfaceType = typeof(ModelInterface.Model.ModelConstraint.IAddUpdate);  
      // Assembly to look under for implementation of above interface  
      var assembly = interfaceType.Assembly;  
 #>  
 using ModelInterface.ModelBinder;  
 using System.Web.Mvc;  
 namespace <#= code.VsNamespaceSuggestion()#>  
 {   
      //------------------------------------------------------------------------------  
      // <auto-generated>  
      //   This code was generated from a template and will be overwritten as soon   
      //       as the template is executed.  
      //  
      //   Changes to this file may cause incorrect behavior and will be lost if  
      //   the code is regenerated.  
      // </auto-generated>  
      //------------------------------------------------------------------------------  
      /// <summary>  
   /// Registers models implementing IAddUpdate interface  
   /// </summary>  
      public static class RegisterIAddUpdateInterface  
      {  
        /// <summary>  
     /// Registers models implementing IAddUpdate interface  
     /// </summary>  
     /// <param name="binder">The binder.</param>  
           public static void RegisterIAddUpdateModels(ModelBinderDictionary binder)  
           {  
                <#  
                foreach (var item in GetInterfaceAssociatedTypes(interfaceType,assembly))  
                {  
                 #>binder.Add(typeof(<#=code.Escape(item.ToString())#>), new InterfaceIAddUpdateModelBinder());  
                 <#  
                }  
           #>  
 }  
      }  
 }  
 <#+  
 // Get all types implementing interface  
 IEnumerable<Type> GetInterfaceAssociatedTypes(Type interfaceType, Assembly assembly)  
 {  
      return (from typ in assembly.GetTypes()  
        where interfaceType.IsAssignableFrom(typ) &&  
                 interfaceType != typ  
        select typ);  
 }  
 #>  

The above T4 template will generate code something similar to below code. Depends upon models.

 using ModelInterface.ModelBinder;  
 using System.Web.Mvc;  
 namespace ModelInterface.App_Start  
 {  
   //------------------------------------------------------------------------------  
   // <auto-generated>  
   //   This code was generated from a template and will be overwritten as soon   
   //       as the template is executed.  
   //  
   //   Changes to this file may cause incorrect behavior and will be lost if  
   //   the code is regenerated.  
   // </auto-generated>  
   //------------------------------------------------------------------------------  
   /// <summary>  
   /// Registers models implementing IAddUpdate interface  
   /// </summary>  
   public static class RegisterIAddUpdateInterface  
   {  
     /// <summary>  
     /// Registers models implementing IAddUpdate interface  
     /// </summary>  
     /// <param name="binder">The binder.</param>  
     public static void RegisterIAddUpdateModels(ModelBinderDictionary binder)  
     {  
       binder.Add(typeof(ModelInterface.Model.DomainModel.UserModel), new InterfaceIAddUpdateModelBinder());  
       binder.Add(typeof(ModelInterface.Model.ViewModel.UserViewModel), new InterfaceIAddUpdateModelBinder());  
     }  
   }  
 }  

We need to pass ModelBinderDictionary to RegisterIAddUpdateModels function for registration of model binding. To do that, in Application_Start event of Global.asax.cs file put this line:

 // Register model binder for IAddUpdate interface implemented models  
 RegisterIAddUpdateInterface.RegisterIAddUpdateModels(ModelBinders.Binders);  

This would set up whole thing. The final touch that we need to do is to have generic function to set up properties value from one object to other.

   /// <summary>  
   /// Type conversion methods  
   /// </summary>  
   public static class TypeConversion  
   {  
     /// <summary>  
     /// Copy values from one object to another implementing <see cref="IAddUpdate"/>  
     /// </summary>  
     /// <typeparam name="TFirstModel">The type of the first model.</typeparam>  
     /// <typeparam name="TSecondModel">The type of the second model.</typeparam>  
     /// <param name="targetModel">The target model.</param>  
     /// <param name="sourceModel">The source model.</param>  
     /// <returns>Changed value model</returns>  
     /// <exception cref="System.ArgumentNullException">  
     /// targetModel  
     /// or  
     /// sourceModel  
     /// </exception>  
     public static TFirstModel ModelConvert<TFirstModel, TSecondModel>(this TFirstModel targetModel,   
       TSecondModel sourceModel)  
       where TFirstModel : IAddUpdate  
       where TSecondModel : IAddUpdate  
     {  
       #region " Null Checks "  
       if (targetModel == null)  
       {  
         throw new ArgumentNullException("targetModel");  
       }  
       if (sourceModel == null)  
       {  
         throw new ArgumentNullException("sourceModel");  
       }  
       #endregion " Null Checks "  
       targetModel.CreatedAt = sourceModel.CreatedAt;  
       targetModel.CreatedBy = sourceModel.CreatedBy;  
       targetModel.UpdatedAt = sourceModel.UpdatedAt;  
       targetModel.UpdatedBy = sourceModel.UpdatedBy;  
       return targetModel;  
     }  
   }  

After changing whole thing let's try up on controller level.

   /// <summary>  
   /// User controller for handling user related operation  
   /// </summary>  
   public class UserController : Controller  
   {  
     /// <summary>  
     /// Indexes this instance.  
     /// </summary>  
     /// <returns></returns>  
     public ActionResult Index()  
     {  
       return View(new UserViewModel());  
     }  
     /// <summary>  
     /// Indexes the specified model.  
     /// </summary>  
     /// <param name="model">The model.</param>  
     /// <returns></returns>  
     [HttpPost]  
     [ValidateAntiForgeryToken]  
     public ActionResult Index(UserViewModel model)  
     {  
       if (!ModelState.IsValid)  
       {  
         return View(model);  
       }  
       var userDomain = new UserModel  
         {  
           Email = model.Email,  
         };  
       // TODO: Save view model's extra properties to different domain model, if needed  
       // Generic extension method for setting up values from one object to another  
       userDomain.ModelConvert(model);  
       // TODO: Check userDomain object while debugging  
       return View(model);  
     }  
   }  

userDomain.ModelConvert(model) will get values from model object and set it to userDomain. If some automapper is used then there is no need of it.


Source code: https://www.dropbox.com/s/0ous4epbz732sr0/ModelInterface.zip

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