[Boiled ASP. NET Web API2 methodology] (1-6) Model Validation

Problem

You want the ASP. NET Web API to perform model validation while sharing some validation logic with ASP.

Solution Solutions

Thesame authentication mechanism that the ASP. NET W eb API supports with ASP. NET MVC is validated by the System.ComponentModel.DataAnnoataions property. Using the relevant validation properties provided by the framework is sufficient to validate the model.

for finer granularity validation, we can choose to implement  ivaludateobjectsystem.componentmodel.dataannotations). If all the properties are verified through, asp.net Web api validate  method, where we can do a further physical validation. This is the same behavior as  mvc  web API   mvc  using the same   Dto

Another way to do this is to use a third- Party library called fluentvalidation (which can download fluentvalidation in NuGet). He can build more powerful validation scenarios. In this case, we still need to implement the Ivalidateobject interface in our model and rely on the fluentvalidation Validator instead of the inline validation logic.

Tip : The authentication behavior of the ASP. NET Web API is the same across the host.

Working principle

In order to Read the model from the HTTP request Body and perform validation, the ASP. NetWeb API relies on a ibodymodelvalidator The service. The approximate description of the interface is shown in Listing 1-17, however, he is an alternative service, under normal circumstances, the default implementation (Defaultbodymodelvalidator) is sufficient forus to use, in the httpconfiguration is set to self-boot.

Listing 1-17. Ibodymodelvalidator interface

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publicinterface IBodyModelValidator{    bool Validate(object model, Type type, ModelMetadataProvider metadataProvider,    HttpActionContext actionContext, stringkeyPrefix);}

   has a service called formatrtparameterbinding  http  request  body  When processing requests bound to  action  parameters, Defaultbodymodelvalidator   validate < The span lang= "ZH-CN" > method is called. For validators, he validates the entire object map recursively, validating each attribute and nested properties. web api  by using dataannotationmodelvalidatorproviderr  wcf   datamemberattribute < Span lang= the "ZH-CN" > declaration, then we need to use the framework of the  datamembervalidatorprovider

Finally, our model can implement the Ivalidatableobject interface, which exposes only a simple method as shown in Listing 1-18 . If the interface is implemented, then we need to provide additional validation logic for ourselves. TheASP. NET WWB API calls the Validate method of the Ivalidateableobject interface as long as all property validation passes.

Listing 1-18. Definition of the Ivalidateableobject interface

1234	publicinterfaceIValidateableObject{    IEnumerable<ValidationResult> Validate(ValidationContext validationContext);}

The results are verified by asp.net Web api    < Span lang= "ZH-CN" >modelstatedictionary  form, here  modelstate  asp.net mvc  The concepts in are identical, but the objects used are different because  web api system.web.http.modelbindingmodelstatedictionary  exposed Isvalid  action model  Verify the status.

The validation mechanism of the

   declaration is also well integrated into  asp.net Web API Help Page api  semantic description. We will discuss him in detail when 7-11 

Tip in the API the best practice is to use different models as Request and Response entities. For example, the entity ID is generally only required by the Response model and can be obtained from the URI if required in the request .

Code

Listing 1-19 shows a scenario in which a model has multiple validations:

RequiredAttribute,maxlengthattribute and

Rangeattribute. Next, we can use modelstate to verify The validation state in the Controller and respond to the appropriate prompt to the caller.

Listing 1-19. Simple WEB API Model validation

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publicclassAlbum{    public intId { get; set; }    [Required(ErrorMessage = "{0} is required")]    [MaxLength(30)]    publicstringArtist { get; set; }    [Required(ErrorMessage = "{0} is required")]    [MaxLength(40)]    publicstringTitle { get; set; }    [Range(0, 10, ErrorMessage = "{0} in the range of {1}-{2} is required.")]    publicintRating { get; set; }}publicclassAlbumController : ApiController{    publicHttpResponseMessage Post(Album album)    {        if(!ModelState.IsValid)        {            thrownewHttpResponseException(Request.CreateErrorResponse(HttpStatusCode.BadRequest,            ModelState));        }        //omitted for brevity    }}

The general validation that handles the Modelstate code can easily be extracted from the Controller into a common part that can be reused well, but this part will be described in detail in 5-4 .

Now, let's consider this scenario, if we want to add two additional attributes Rating and starred to the model , while extending the model validation, the requirement for validation is that at least one of these two properties is required. Although the validation of entanglement between the two attributes is difficult to express in a declarative way, don't forget that ivalidateableobject can help us. We can use the Validata method in the interface to check the state of the entire model and return the corresponding Validationresult. The code we want to make is as shown in Listing 1-20.

Listing 1-20. Modifying the ASP. NET Web API relies on ivalidateableobject validation

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publicclass Album : IValidatableObject{    publicintId { get; set; }     [Required(ErrorMessage = "{0} is required")]    [MaxLength(30)]    publicstringArtist { get; set; }     [Required(ErrorMessage = "{0} is required")]    [MaxLength(40)]    publicstringTitle { get; set; }     publicint? Rating { get; set; }    publicbool? Starred { get; set; }     publicIEnumerable<ValidationResult> Validate(ValidationContext validationContext)    {        if(!(Rating.HasValue && Rating > 0 && Rating < 10) || (Starred.HasValue && Starred.Value))        {            yield returnnewValidationResult("You must set either the Rating in the 0-9 range orStarred flag.");        }    }}

[Boiled ASP. NET Web API2 methodology] (1-6) Model Validation