ASP. NET Web API Model-ValueProvider,

ASP. NET Web API Model-ValueProvider,
ASP. NET Web API Model-ValueProvider Preface

The previous article explains Model metadata. Model metadata is an important part of Model binding. It only involves a lot of knowledge points in Model binding. for ASP. net mvc Framework ASP. in the "Model binding" section of the NET Web API framework, a parameter binding mechanism is added, which will be described later, the previous sections explain theoretical knowledge and do not involve demonstration of examples. You don't have to worry about connecting all the previous sections after the basic knowledge of the last Model, today, this article will bring you a crucial link in Model binding. You don't have to worry about Model binding, instead, we simply understand the ValueProvider series of object models, because we do not know where the ValueProvider is executed until it is combined with the knowledge points. So let's take a closer look at the ValueProvider-related objects.

 

Model-ValueProvider

Figure 1

 

IValueProviderInterface Type-- ValueProviderBehavior constraints

First, let's take a look at the right part of Section 1. The header is an IValueProvider interface type. Let's take a look at the interface definition:

Sample Code 1-1

    public interface IValueProvider    {        bool ContainsPrefix(string prefix);        ValueProviderResult GetValue(string key);    }

We can see in code 1-1 that the IValueProvider interface defines two methods. One is the ContainsPrefix () method, which receives parameters of the string type and returns the bool value type, this method is used to check whether this prefix value exists in the current ValueProvider Based on the specified prefix value. The following example will be used later, followed by the GetValue () method, returns the corresponding value based on the executed key value. From this point of view, we can probably guess that this ValueProvider should be of the same type as the key value team, the returned results are encapsulated in the ValueProviderResult type, which will be described later. After the IValueProvider interface limits the behavior of the ValueProvider value provider, let's take a look at the basic structure of the ValueProvider value provider. But before that, we still need to take a look at the definition of the IEnumerableValueProvider interface type as shown in Figure 1. What is the main responsibility of this interface?

 

IEnumerableValueProviderInterface Type-ValueProviderBehavior constraints

Sample Code 1-2

    public interface IEnumerableValueProvider : IValueProvider    {        IDictionary<string, string> GetKeysFromPrefix(string prefix);    }

From code 1-2, we can clearly see that the role of the IEnumerableValueProvider interface type is very simple, that is, to retrieve the specified prefix value and finally return it as a key-value team, this example is described in detail below.

 

NameValuePairsValueProviderType-ValueProviderInfrastructure

Sample Code 1-3

    public class NameValuePairsValueProvider : IEnumerableValueProvider, IValueProvider    {        public NameValuePairsValueProvider(Func<IEnumerable<KeyValuePair<string, string>>> valuesFactory, CultureInfo culture);        public NameValuePairsValueProvider(IEnumerable<KeyValuePair<string, string>> values, CultureInfo culture);        public virtual bool ContainsPrefix(string prefix);        public virtual IDictionary<string, string> GetKeysFromPrefix(string prefix);        public virtual ValueProviderResult GetValue(string key);    }

In code 1-3, we can see the definition of the NameValuePairsValueProvider type. Let's talk about its constructor. The difference between the two constructor is that the first one is Func <IEnumerable <KeyValuePair <string, string >>> Type constructor parameter, and the second is IEnumerable <KeyValuePair <string, string> Type constructor parameter, the first parameter type of the second constructor is actually the return type of the first parameter of the first constructor. As you can see here, it is actually implemented internally, this is also the case where it is okay to declare the first constructor. When declaring the Second constructor, the parameter is actually encapsulated as a delegate again.

For the KeyValuePair <T, U> type, it can be understood as a subitem of the key-value team. In its type, only one key value corresponds to one value and only one key value is itself.

As for the remaining three methods, let's use a simple example to illustrate them.

Sample Code 1-4

Public class ValueProviderCaseController: ApiController {public string Get () {KeyValuePair <string, string> [] dictionary = new KeyValuePair <string, string> [] {new KeyValuePair <string, string> ("EmployeesInfo. name "," Jinyuan "), new KeyValuePair <string, string> (" EmployeesInfo. age "," 24 "), new KeyValuePair <string, string> (" EmployeesInfo. sex "," male "), new KeyValuePair <string, string> (" EmployeesInfo. addressInfo. ad DressInfo "," Nanjing "), new KeyValuePair <string, string> (" EmployeesInfo. addressInfo. zipCode "," 210000 ")}; region identifier = new NameValuePairsValueProvider (dictionary, null); StringBuilder strBuilder = new StringBuilder (); NameValuePairsPrefixAnalysis (strBuilder, struct," EmployeesInfo "); return strBuilder. toString ();} private void NameValuePair SPrefixAnalysis (StringBuilder stringbuilder, NameValuePairsValueProvider namevaluepairs, string prefix) {IDictionary <string, string> dictionarys = namevaluepairs. getKeysFromPrefix (prefix); if (dictionarys. count> 0) {Console. writeLine (prefix + "data source Key value retrieval with the prefix ...... "); Foreach (var item in dictionarys) {Console. writeLine ("Key:" + item. key + "Value:" + item. value);} foreach (KeyValuePair <string, string> keyvalue in dictionarys) {NameValuePairsPrefixAnalysis (stringbuilder, namevaluepairs, keyvalue. value) ;}} else {stringbuilder. appendLine (prefix + ":" + namevaluepairs. getValue (prefix ). rawValue. toString ());}}}

Let's take a look at code 1-4. First, I defined a KeyValuePair <string, string> [] type in the Get () method. to instantiate the NameValuePairsValueProvider type, after that, you can see that I have called a custom NameValuePairsPrefixAnalysis () method, and the GetKeysFromPrefix () method is called by using an instance of the NameValuePairsValueProvider type, that is, the behavior restricted by code 1-2. At this time, let's first look at table 1.

 

Table 1

Key	Value
EmployeesInfo. Name	Jinyuan
EmployeesInfo. Age	24
EmployeesInfo. Sex	Male
EmployeesInfo. AddressInfo. AddressInfo	Nanjing
EmployeesInfo. AddressInfo. ZipCode	210000

Table 1 represents the initial data source, that is, the KeyValuePair <string, string> [] type key and value table.

However, the IDictionary <string, string> type values returned after the GetKeysFromPrefix () method is called using an instance of the NameValuePairsValueProvider type "EmployeesInfo" as the prefix, as shown in table 2.

 

Table 2

Key	Value
Name	EmployeesInfo. Name
Age	EmployeesInfo. Age
Sex	EmployeesInfo. Sex
AddressInfo	EmployeesInfo. AddressInfo

The value of Table 2 here is only the Relational Value of the first layer.

After that, we output the current prefix Value to be retrieved and the retrieved Value, and traverse the Value in Table 2 as the prefix Value to re-search the data source for the prefix, if no, it indicates that no search is available.

The GetValue () method called by an instance of NameValuePairsValueProvider type cannot be found based on the suffix prefix value, that is, the Key value in the original data source.

Finally, let's take a look at the results.

Figure 2

We obtained the value from the client. Of course, this is just a demo. The value direction provided by the value provider is reversed.

Then we can see the retrieved records on the server, and we can clearly see that there are two layers of structure in it. If you are interested, take a closer look at the specific implementation of the search.

 

QueryStringValueProviderType-ValueProviderSpecific Structure

Sample Code 1-5

    public class QueryStringValueProvider : NameValuePairsValueProvider    {        public QueryStringValueProvider(HttpActionContext actionContext, CultureInfo culture)            : base(func, culture)        {            Func<IEnumerable<KeyValuePair<string, string>>> func = null;            if (func == null)            {                func = () => actionContext.ControllerContext.Request.GetQueryNameValuePairs();            }        }    }

From code 1-5, we can see the execution of the constructor during the initialization of the QueryStringValueProvider type, encapsulate the request query string as the original data source as the delegate type, and then call the constructor of the base class.

 

RouteDataValueProviderType-ValueProviderSpecific Structure

Sample Code 1-6

    public class RouteDataValueProvider : NameValuePairsValueProvider    {        public RouteDataValueProvider(HttpActionContext actionContext, CultureInfo culture)            : base(func, culture)        {            Func<IEnumerable<KeyValuePair<string, string>>> func = null;            if (func == null)            {                func = () => GetRoutes(actionContext.ControllerContext.RouteData);            }        }    }

In the same way as 1-5 above, the Values value in HttpRouteData is used as the original data source.

The left part of Figure 1 will be explained in the subsequent sections. It is not suitable and will be incoherent, although I do not know what role this plays or how to use it after reading this article, I feel as uncomfortable as being shackled by my neck, however, in the future, I will concatenate all the content mentioned above for a demonstration. This is the basic knowledge and a foreshadowing.

 

 

Author: Jin Yuan

Source: http://www.cnblogs.com/jin-yuan/

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