public abstract class ActionFilterAttribute : Attribute, IActionFilter, IFilterMetadata, IAsyncActionFilter, IResultFilter, IAsyncResultFilter, IOrderedFilter<\/code><\/pre>\nTo implement the synchronous Action filter that runs before and after action method execution, we need to implement the OnActionExecuting and OnActionExecuted methods:
\n\u8981\u5b9e\u73b0\u5728\u4f5c\u65b9\u6cd5\u6267\u884c\u4e4b\u524d\u548c\u4e4b\u540e\u8fd0\u884c\u7684\u540c\u6b65 Action \u8fc7\u6ee4\u5668\uff0c\u6211\u4eec\u9700\u8981\u5b9e\u73b0 OnActionExecuting \u548c OnActionExecuted \u65b9\u6cd5\uff1a<\/p>\n
namespace ActionFilters.Filters\n{\n public class ActionFilterExample : IActionFilter\n {\n public void OnActionExecuting(ActionExecutingContext context)\n {\n \/\/ our code before action executes\n \/\/\n }\n public void OnActionExecuted(ActionExecutedContext context)\n {\n \/\/ our code after action executes\n }\n }\n}<\/code><\/pre>\nWe can do the same thing with an asynchronous filter by inheriting from IAsyncActionFilter, but we only have one method to implement \u2014 the OnActionExecutionAsync:
\n\u6211\u4eec\u53ef\u4ee5\u901a\u8fc7\u4ece IAsyncActionFilter \u7ee7\u627f\u6765\u5bf9\u5f02\u6b65\u7b5b\u9009\u5668\u6267\u884c\u76f8\u540c\u7684\u4f5c\uff0c\u4f46\u6211\u4eec\u53ea\u6709\u4e00\u79cd\u65b9\u6cd5\u8981\u5b9e\u73b0 \u2014 OnActionExecutionAsync\uff1a<\/p>\n
namespace ActionFilters.Filters\n{\n public class AsyncActionFilterExample : IAsyncActionFilter\n {\n public async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)\n {\n \/\/ execute any code before the action executes\n var result = await next();\n \/\/ execute any code after the action executes\n }\n }\n}<\/code><\/pre>\n15.2 The Scope of Action Filters<\/h2>\n
15.2\u4f5c\u7b5b\u9009\u5668\u7684\u8303\u56f4<\/p>\n
Like the other types of filters, the action filter can be added to different scope levels: Global, Action, and Controller.\u200c
\n\u4e0e\u5176\u4ed6\u7c7b\u578b\u7684\u7b5b\u9009\u5668\u4e00\u6837\uff0c\u4f5c\u7b5b\u9009\u5668\u53ef\u4ee5\u6dfb\u52a0\u5230\u4e0d\u540c\u7684\u8303\u56f4\u7ea7\u522b\uff1aGlobal\u3001Action \u548c Controller\u3002<\/p>\n
If we want to use our filter globally, we need to register it inside the AddControllers() method in the Program class:
\n\u5982\u679c\u6211\u4eec\u60f3\u5168\u5c40\u4f7f\u7528\u6211\u4eec\u7684\u8fc7\u6ee4\u5668\uff0c\u6211\u4eec\u9700\u8981\u5728 Program \u7c7b\u7684 AddControllers\uff08\uff09 \u65b9\u6cd5\u4e2d\u6ce8\u518c\u5b83\uff1a<\/p>\n
builder.Services.AddControllers(config => { config.Filters.Add(new GlobalFilterExample()); });<\/code><\/pre>\nBut if we want to use our filter as a service type on the Action or Controller level, we need to register it, but as a service in the IoC container:
\n\u4f46\u662f\uff0c\u5982\u679c\u6211\u4eec\u60f3\u5c06\u8fc7\u6ee4\u5668\u7528\u4f5c Action \u6216 Controller \u7ea7\u522b\u7684\u670d\u52a1\u7c7b\u578b\uff0c\u5219\u9700\u8981\u5c06\u5176\u6ce8\u518c\uff0c\u4f46\u8981\u4f5c\u4e3a IoC \u5bb9\u5668\u4e2d\u7684\u670d\u52a1\u8fdb\u884c\u6ce8\u518c\uff1a<\/p>\n
builder.Services.AddScoped<ActionFilterExample>(); \nbuilder.Services.AddScoped<ControllerFilterExample>();<\/code><\/pre>\nFinally, to use a filter registered on the Action or Controller level, we need to place it on top of the Controller or Action as a ServiceType:
\n\u6700\u540e\uff0c\u8981\u4f7f\u7528\u5728 Action \u6216 Controller \u7ea7\u522b\u6ce8\u518c\u7684\u8fc7\u6ee4\u5668\uff0c\u6211\u4eec\u9700\u8981\u5c06\u5176\u4f5c\u4e3a ServiceType \u653e\u5728 Controller \u6216 Action \u7684\u9876\u90e8\uff1a<\/p>\n
namespace AspNetCore.Controllers\n{\n [ServiceFilter(typeof(ControllerFilterExample))]\n [Route("api\/[controller]")]\n [ApiController]\n public class TestController : ControllerBase\n {\n [HttpGet]\n [ServiceFilter(typeof(ActionFilterExample))]\n public IEnumerable<string> Get()\n {\n return new string[] { "example", "data" };\n }\n }\n}<\/code><\/pre>\n15.3 Order of Invocation<\/h2>\n
15.3 \u8c03\u7528\u987a\u5e8f<\/p>\n
The order in which our filters are executed is as follows:\u200c
\n\u8fc7\u6ee4\u5668\u7684\u6267\u884c\u987a\u5e8f\u5982\u4e0b\uff1a<\/p>\n
![\"alt](\"\/images\/ultimateaspnetcorewebapi6\/1501.jpg\")
<\/p>\n
Of course, we can change the order of invocation by adding the Order property to the invocation statement:
\n\u5f53\u7136\uff0c\u6211\u4eec\u53ef\u4ee5\u901a\u8fc7\u5c06 Order \u5c5e\u6027\u6dfb\u52a0\u5230\u8c03\u7528\u8bed\u53e5\u6765\u66f4\u6539\u8c03\u7528\u987a\u5e8f\uff1a<\/p>\n
namespace AspNetCore.Controllers\n{\n [ServiceFilter(typeof(ControllerFilterExample), Order = 2)]\n [Route("api\/[controller]")]\n [ApiController]\n public class TestController : ControllerBase\n {\n [HttpGet]\n [ServiceFilter(typeof(ActionFilterExample), Order = 1)]\n public IEnumerable<string> Get()\n {\n return new string[] { "example", "data" };\n }\n }\n}<\/code><\/pre>\nOr something like this on top of the same action:
\n\u6216\u8005\uff0c\u5728\u76f8\u540c\u7684\u4f5c\u4e4b\u4e0a\uff0c\u5982\u4e0b\u6240\u793a\uff1a<\/p>\n
[HttpGet]\n[ServiceFilter(typeof(ActionFilterExample), Order = 2)] \n[ServiceFilter(typeof(ActionFilterExample2), Order = 1)] \npublic IEnumerable<string> Get() \n{ \n return new string[] { "example", "data" }; \n}<\/code><\/pre>\n15.4 Improving the Code with Action Filters<\/h2>\n
15.4 \u4f7f\u7528 Action Filters \u6539\u8fdb\u4ee3\u7801<\/p>\n
Our actions are clean and readable without try-catch blocks due to global exception handling and a service layer implementation, but we can improve them even further.\u200c
\n\u7531\u4e8e\u5168\u5c40\u5f02\u5e38\u5904\u7406\u548c\u670d\u52a1\u5c42\u5b9e\u73b0\uff0c\u6211\u4eec\u7684\u4f5c\u5e72\u51c0\u4e14\u53ef\u8bfb\uff0c\u6ca1\u6709 try-catch \u5757\uff0c\u4f46\u6211\u4eec\u53ef\u4ee5\u8fdb\u4e00\u6b65\u6539\u8fdb\u5b83\u4eec\u3002<\/p>\n
So, let\u2019s start with the validation code from the POST and PUT actions.
\n\u56e0\u6b64\uff0c\u8ba9\u6211\u4eec\u4ece POST \u548c PUT\u4f5c\u4e2d\u7684\u9a8c\u8bc1\u4ee3\u7801\u5f00\u59cb\u3002<\/p>\n
15.5 Validation with Action Filters<\/h2>\n
15.5 \u4f7f\u7528\u52a8\u4f5c\u8fc7\u6ee4\u5668\u8fdb\u884c\u9a8c\u8bc1<\/p>\n
If we take a look at our POST and PUT actions, we can notice the repeated code in which we validate our Company model:\u200c
\n\u5982\u679c\u6211\u4eec\u770b\u4e00\u4e0b POST \u548c PUT\u4f5c\uff0c\u6211\u4eec\u4f1a\u6ce8\u610f\u5230\u9a8c\u8bc1 Company \u6a21\u578b\u7684\u91cd\u590d\u4ee3\u7801\uff1a<\/p>\n
if (company is null) \n return BadRequest("CompanyForUpdateDto object is null"); \nif (!ModelState.IsValid) \n return UnprocessableEntity(ModelState);<\/code><\/pre>\nWe can extract that code into a custom Action Filter class, thus making this code reusable and the action cleaner.
\n\u6211\u4eec\u53ef\u4ee5\u5c06\u8be5\u4ee3\u7801\u63d0\u53d6\u5230\u81ea\u5b9a\u4e49 Action Filter \u7c7b\u4e2d\uff0c\u4ece\u800c\u4f7f\u6b64\u4ee3\u7801\u53ef\u91cd\u7528\u4e14\u4f5c\u66f4\u7b80\u6d01\u3002<\/p>\n
So, let\u2019s do that.
\n\u6240\u4ee5\uff0c\u8ba9\u6211\u4eec\u5f00\u59cb\u5427\u3002<\/p>\n
Let\u2019s create a new folder in our solution explorer, and name it ActionFilters. Then inside that folder, we are going to create a new class ValidationFilterAttribute:
\n\u8ba9\u6211\u4eec\u5728\u89e3\u51b3\u65b9\u6848\u8d44\u6e90\u7ba1\u7406\u5668CompanyEmployees.Presentation\u4e2d\u521b\u5efa\u4e00\u4e2a\u65b0\u6587\u4ef6\u5939\uff0c\u5e76\u5c06\u5b83 ActionFilters \u7684 API \u4e2d\u3002\u7136\u540e\u5728\u8be5\u6587\u4ef6\u5939\u4e2d\uff0c\u6211\u4eec\u5c06\u521b\u5efa\u4e00\u4e2a\u65b0\u7c7b ValidationFilterAttribute\uff1a<\/p>\n
using Microsoft.AspNetCore.Mvc.Filters;\n\nnamespace CompanyEmployees.Presentation.ActionFilters\n{\n public class ValidationFilterAttribute : IActionFilter\n {\n public ValidationFilterAttribute() { }\n public void OnActionExecuting(ActionExecutingContext context) { }\n public void OnActionExecuted(ActionExecutedContext context) { }\n }\n}<\/code><\/pre>\nNow we are going to modify the OnActionExecuting method:
\n\u73b0\u5728\uff0c\u6211\u4eec\u5c06\u4fee\u6539 OnActionExecuting \u65b9\u6cd5\uff1a<\/p>\n
using Microsoft.AspNetCore.Mvc;\nusing Microsoft.AspNetCore.Mvc.Filters;\n\nnamespace CompanyEmployees.Presentation.ActionFilters\n{\n public class ValidationFilterAttribute : IActionFilter\n {\n public ValidationFilterAttribute() { }\n \/\/ public void OnActionExecuting(ActionExecutingContext context) { }\n public void OnActionExecuting(ActionExecutingContext context)\n {\n var action = context.RouteData.Values["action"];\n var controller = context.RouteData.Values["controller"];\n\n var param = context.ActionArguments.SingleOrDefault(x => x.Value.ToString().Contains("Dto")).Value;\n if (param is null)\n {\n context.Result = new BadRequestObjectResult($"Object is null. Controller: {controller}, action: {action}"); \n return;\n }\n if (!context.ModelState.IsValid) \n context.Result = new UnprocessableEntityObjectResult(context.ModelState);\n }\n public void OnActionExecuted(ActionExecutedContext context) { }\n }\n}<\/code><\/pre>\nWe are using the context parameter to retrieve different values that we need inside this method. With the RouteData.Values dictionary, we can get the values produced by routes on the current routing path. Since we need the name of the action and the controller, we extract them from the Values dictionary.
\n\u6211\u4eec\u4f7f\u7528 context \u53c2\u6570\u6765\u68c0\u7d22\u6b64\u65b9\u6cd5\u4e2d\u6240\u9700\u7684\u4e0d\u540c\u503c\u3002\u4f7f\u7528 RouteData.Values \u5b57\u5178\uff0c\u6211\u4eec\u53ef\u4ee5\u83b7\u53d6\u5f53\u524d\u8def\u7531\u8def\u5f84\u4e0a\u7684\u8def\u7531\u751f\u6210\u7684\u503c\u3002\u7531\u4e8e\u6211\u4eec\u9700\u8981\u4f5c\u548c\u63a7\u5236\u5668\u7684\u540d\u79f0\uff0c\u56e0\u6b64\u6211\u4eec\u4ece Values \u5b57\u5178\u4e2d\u63d0\u53d6\u5b83\u4eec\u3002<\/p>\n
Additionally, we use the ActionArguments dictionary to extract the DTO parameter that we send to the POST and PUT actions. If that parameter is null, we set the Result property of the context object to a new instance of the BadRequestObjectReturnResult class. If the model is invalid, we create a new instance of the UnprocessableEntityObjectResult class and pass ModelState.
\n\u6b64\u5916\uff0c\u6211\u4eec\u4f7f\u7528 ActionArguments \u5b57\u5178\u6765\u63d0\u53d6\u6211\u4eec\u53d1\u9001\u5230 POST \u548c PUT\u4f5c\u7684 DTO \u53c2\u6570\u3002\u5982\u679c\u8be5\u53c2\u6570\u4e3a null\uff0c\u5219\u6211\u4eec\u5c06\u4e0a\u4e0b\u6587\u5bf9\u8c61\u7684 Result \u5c5e\u6027\u8bbe\u7f6e\u4e3a BadRequestObjectReturnResult \u7c7b\u7684\u65b0\u5b9e\u4f8b\u3002\u5982\u679c\u6a21\u578b\u65e0\u6548\uff0c\u6211\u4eec\u5c06\u521b\u5efa UnprocessableEntityObjectResult \u7c7b\u7684\u65b0\u5b9e\u4f8b\u5e76\u4f20\u9012 ModelState\u3002<\/p>\n
Next, let\u2019s register this action filter in the Program class above the AddControllers method:
\n\u63a5\u4e0b\u6765\uff0c\u8ba9\u6211\u4eec\u5728 AddControllers \u65b9\u6cd5\u4e0a\u65b9\u7684 Program \u7c7b\u4e2d\u6ce8\u518c\u6b64\u4f5c\u7b5b\u9009\u5668\uff1a<\/p>\n
builder.Services.AddScoped<ValidationFilterAttribute>();<\/code><\/pre>\nFinally, let\u2019s remove the mentioned validation code from our actions and call this action filter as a service.
\n\u6700\u540e\uff0c\u8ba9\u6211\u4eec\u4ece\u4f5c\u4e2d\u5220\u9664\u63d0\u5230\u7684\u9a8c\u8bc1\u4ee3\u7801\uff0c\u5e76\u5c06\u6b64\u4f5c\u7b5b\u9009\u6761\u4ef6\u4f5c\u4e3a\u670d\u52a1\u8c03\u7528\u3002<\/p>\n
POST:<\/p>\n
[HttpPost]\n[ServiceFilter(typeof(ValidationFilterAttribute))]\npublic async Task<IActionResult> CreateCompany([FromBody] CompanyForCreationDto company)\n{\n if (company is null)\n return BadRequest("CompanyForCreationDto object is null");\n\n if (!ModelState.IsValid)\n return UnprocessableEntity(ModelState);\n\n var createdCompany = await _service.CompanyService.CreateCompanyAsync(company);\n\n return CreatedAtRoute("CompanyById", new { id = createdCompany.Id }, createdCompany);\n}<\/code><\/pre>\nPUT:<\/p>\n
[HttpPut("{id:guid}")]\n[ServiceFilter(typeof(ValidationFilterAttribute))]\npublic async Task<IActionResult> UpdateCompany(Guid id, [FromBody] CompanyForUpdateDto company)\n{\n if (company is null)\n return BadRequest("CompanyForUpdateDto object is null");\n\n if (!ModelState.IsValid)\n return UnprocessableEntity(ModelState);\n\n await _service.CompanyService.UpdateCompanyAsync(id, company, trackChanges: true);\n\n return NoContent();\n}<\/code><\/pre>\nExcellent.
\n\u975e\u5e38\u597d\u3002<\/p>\n
This code is much cleaner and more readable now without the validation part. Furthermore, the validation part is now reusable for the POST and PUT actions for both the Company and Employee DTO objects.
\n\u73b0\u5728\uff0c\u6ca1\u6709\u9a8c\u8bc1\u90e8\u5206\uff0c\u6b64\u4ee3\u7801\u66f4\u52a0\u6e05\u6670\u6613\u8bfb\u3002\u6b64\u5916\uff0c\u9a8c\u8bc1\u90e8\u5206\u73b0\u5728\u53ef\u91cd\u590d\u7528\u4e8e Company \u548c Employee DTO \u5bf9\u8c61\u7684 POST \u548c PUT\u4f5c\u3002<\/p>\n
If we send a POST request, for example, with the invalid model we will get the required response:
\n\u4f8b\u5982\uff0c\u5982\u679c\u6211\u4eec\u53d1\u9001 POST \u8bf7\u6c42\uff0c\u4f7f\u7528\u65e0\u6548\u6a21\u578b\uff0c\u6211\u4eec\u5c06\u83b7\u5f97\u6240\u9700\u7684\u54cd\u5e94\uff1a<\/p>\n
![\"alt](\"\/images\/ultimateaspnetcorewebapi6\/1502.jpg\")
<\/p>\n![\"alt](\"\/images\/ultimateaspnetcorewebapi6\/1503.jpg\")
<\/p>\n