asp.net MVC example Project "Suteki.shop" Analysis of Modelbinder

In Suteki.shop, the author constructs a modelbinder base class "DataBinder", which itself inherits from the Imodelbinder interface and derives other subclass classes such as Productbinder, and so on, with this class. It can be said that, in addition to the very few places, DataBinder was used to suteki.shop most of the modelbinder bound scenes.

First look at its class diagram structure:

As a base class, DataBinder (the lower left of the figure) implements converting the HTTP request data into the corresponding type in the model. The core approach is Bindmodel, and here's how to explain:

public　virtual　object　BindModel(ControllerContext　controllerContext,　 ModelBindingContext　bindingContext)
{
object　entity;

if (declaringAttribute　==　null　||　declaringAttribute.Fetch)
{
entity　=　 FetchEntity(bindingContext,　controllerContext);
}
else
{
entity　=　 Activator.CreateInstance(bindingContext.ModelType);
}

try
{
validatingBinder.UpdateFrom(entity,　 controllerContext.HttpContext.Request.Form,　bindingContext.ModelState,　 bindingContext.ModelName);
}
catch(ValidationException　ex)
{
//Ignore　validation　exceptions　-　they　are　stored　in　ModelState.
//The　 controller　can　access　the　errors　by　inspecting　the　ModelState　dictionary.
}

return　entity;
}

The first thing to explain is declaringattribute, a variable that is actually a Databindattribute type instance, and its role is to determine whether the currently requested data is used to create new model information or to acquire and bind existing data records. The actual initialization of the instance is given to the Accept method (note that the declaration of the Accept method is defined in the Iacceptsattribute interface):

public　void　Accept(Attribute　attribute)
{
declaringAttribute　=　 (DataBindAttribute)　attribute;
}

The call to the method is placed in the Bindusingattribute Getbinder () method, so here's a look at the specific implementation of Bindusingattribute:

public　class　BindUsingAttribute　:　CustomModelBinderAttribute
{
private　readonly　Type　binderType;

public　BindUsingAttribute(Type　 binderType)
{
if(!typeof(IModelBinder).IsAssignableFrom(binderType))
{
throw　new　InvalidOperationException("Type　'{0}'　does　not　implement　 IModelBinder.".With(binderType.Name));
}

this.binderType　=　 binderType;
}

public　override　IModelBinder　GetBinder()
{
var　 binder　=　(IModelBinder)　ServiceLocator.Current.GetInstance(binderType);

if (binder　is　IAcceptsAttribute)
{
((IAcceptsAttribute)binder).Accept(this);
}

return　binder;
}
}

This property class is used for modelbinder binding in action, and its class constructor is initialized with a type parameter and used in the Getbinder () method Servicelocator to perform the final Modelbinder instantiation, note that in this method there is a logical judgment of the current binder (Iacceptsattribute), and to distinguish whether the modelbinder of the current action binding implements the Iacceptsattribute interface. If not implemented or Declaringattribute.fetch is true, the Fetchentity () method is invoked in the previous DataBinder class method "Bindmodel". Fetchentity retrieves the data from the primary key (PrimaryKey) in the submitted data and returns the object instance with the following code:

private　object　FetchEntity(ModelBindingContext　bindingContext,　 ControllerContext　controllerContext)
{
object　entity;
var　primaryKey　=　 bindingContext.ModelType.GetPrimaryKey();//从Shop.dbml中查找相应的主键信息
string　 name　=　bindingContext.ModelName　+　"."　+　primaryKey.Name;//拼接出要获取的主 键名称

string　rawKeyValue　=　controllerContext.HttpContext.Request.Form [name];

if　(string.IsNullOrEmpty(rawKeyValue))
{
throw　new　 InvalidOperationException("Could　not　find　a　value　named　'{0} '".With(name));
}

int　key　=　Convert.ToInt32(rawKeyValue);
var　repository　=　resolver.GetRepository(bindingContext.ModelType);
entity　=　 repository.GetById(key);
return　entity;
}

Notice the two lines in the above code:

var　repository　=　resolver.GetRepository(bindingContext.ModelType);
entity　=　repository.GetById(key);