22nd Chapter Model Binding

Model Binding is the process of creating a. NET object with data that the browser sends in an HTTP request.

The parameters of the action method depend on the model binding process (implemented through the model binder). The process of constructing the parameter objects required by the action method using the data that the entire HTTP request carries (the data that the user enters in the form, the routing data, the query string in the request URL, the file that is uploaded in the request).

Model binding process (what the model Binder will do):

1. Detect the name and type of the target object (the object to be created, the parameter of the action method); ( the name and type of the action method parameter )

2. Find the data source (request) by object name and find the available data (usually a string); ( find string data with name matching in the request data )

3. Converts the found data value to the target type based on the object type; ( converts the string type data to the type of the action method parameter )

4. Construct the target object by object name, object type, and such processed data; ( an object using the above data to construct an action method parameter )

5. Pass the constructed object to the action Invoker and inject the object into the target action method by the action Invoker. ( passing the target object to the action method )

Caller: Iactioninvoker

Default caller: Controlleractioninvoker

Model Binder: Imodelbinder

Default model binder: Defaultmodelbinder

Requests: Request

Request data: Request.Form, Request.Files, Routedata.values, Request.QueryString

Models: Model

Model Properties: Model.name

Property Type: String

Controllers: Controller

Action method: Action

Action parameter: Actionparam

Parameter type: string

Parameter value: "AA"

First, the default model binder

　The Defaultmodelbinder class finds the order of parameter data (stops if found)

Data source	Describe	Example
Request.Form	data that is provided (filled in) by the user in the HTML form	request.form["id"]
Routedata.values	Values obtained with application routing	routedata.values["id"]
Request.QueryString	Part of the data contained in the query string in the request URL	request.querystring["id"]
Request.Files	Files uploaded in the request	request.files["id"]

　　　　1. Composite type binding : A property (Simple type: string, int ...) when the argument of an action method is a composite type (cannot be converted with the TypeConverter class. ), use reflection to get the public property set, and then bind in turn.

(1) Easy-to-bind HTML:

　　　　　　

    <div> @Html. labelfor (M = m.homeaddress.city)           and m.homeaddress.city)    </ Div>    

<div><label for= "Homeaddress_city" > City </label>
<input class= "Text-box single-line" id= "homeaddress_city" name= "homeaddress.city" type= "text" value= ""/>
</div>

(2) Specifying a custom prefix:

Data with a binding prefix of "homeaddress"

         Public " homeaddress " ) {]addresssummary summary        )            {return  View (summary);        }

(3) To selectively bind attributes:

Exclude bindings for the country property

         Public " homeaddress " " Country " ) {]addresssummary summary        )            {return  View (summary);        }

Specifying the properties of a binding

When this class is bound, only the city property is bound, excluding other properties

    "  City " )]    publicclass  addresssummary    {        publicstring  getset;}          Public string Get Set ; }    }

Second, manual call model binding

1.UpdateModel (Parameter list) method:

 Public ActionResult Address (ilist<addresssummary> addresses)        {            new list< Addresssummary>();            Updatemodel (addresses,new// Restrict binding source to form content             return View (addresses);        }

Value provider: Ivalueprovider

Built-in Ivalueprovider implementation

Data source	Ivalueprovider implementation
Request.Form	Formvalueprovider
Routedata.values	Routedatavalueprovider
Request.QueryString	Querystringvalueprovider
Request.Files	Httpfilecollectionvalueprovider

Improvement: The most common limitation is to find only the form values:

 Public actionresult Address (formcollection formData)        {            IListnew list<addresssummary>();            Updatemodel (addresses, formData);             return View (addresses);        }

　　2. Handling Binding Errors

Note: binding errors do not emit an abnormal signal when model bindings are called automatically. The results must be checked through the Modelstate.isvalid property.

InvalidOperationException exception indicates binding error

 public   ActionResult Address ( FormCollection formData) {IList  <AddressSummary> addresses = new  list<addresssummary> ();  if   (TryUpdateModel (addresses, FormData ) { // todo: Bind normal Operation    { // todo: Bind exception Action   return   View (addresses); }

III. Custom Model Binding system (Imodelbinder)

1. Custom Value Providers

The most valuable attribute defined by the Modelbindingcontext class

Property	Describe
Model	If the binding is called manually, you can return the model object passed to the Updatemodel method
ModelName	Returns the name of the model being bound
Modeltype	Returns the type of the model being created
Valueprovider	Returns the Ivalueprovider implementation that can be used to fetch data values from the request

Tip: Modelbinder annotation properties and custom model binders to change the default model binder.

22nd Chapter Model Binding