ActionFilter equivalent in Asp.net Core Razor Pages

Question

First off all,I know there is no Action Filter in asp.net core razor pages.But I am searching to find a mechanism that works similar. What I am trying to achieve is to apply filter based on handler methods.When I try to use pagefilter, it is applied to all methods.Is there any method/way to exclude some handler methods on the same page ?

To clarify question I added some examples.

Here is example pagefilter

public class FormValidatorRazor : IAsyncPageFilter
{
    public async Task OnPageHandlerExecutionAsync(PageHandlerExecutingContext context, PageHandlerExecutionDelegate next)
    {
        if (context.HttpContext.Request.Method.Equals("POST") || context.HttpContext.Request.Method.Equals("PUT"))
        //code removed for brevity
 }

Here is how I apply it to the project

public void ConfigureServices(IServiceCollection services)
{
    services.AddRazorPages().AddMvcOptions(options =>
    {
        options.Filters.Add(new FormValidatorRazor());
        //code removed for brevity
    }
}

Here is example handler methods.

public async Task<IActionResult> OnPostUpdate(ExModel model)
{
}

public async Task<IActionResult> OnPostEdit(ExModel model)
{
}

I want my filter to be applied to OnPostUpdate but not to OnPostEdit.How can I achieve that behaviour ?

Answer 1

The PageHandlerExecutingContext parameter passed in to OnPageHandlerExecutionAsync provides everything you need to achieve this. Here's an example that shows the specifics:

public async Task OnPageHandlerExecutionAsync(
    PageHandlerExecutingContext context, PageHandlerExecutionDelegate next)
{
    if (context.HandlerMethod?.Name == "Update")
    {
        // Running inside a handler method named "Update".
    }

    // ...
}

HandlerMethod is non-null when a handler method is being executed. It provides these properties, that might be of interest:

• HttpMethod, e.g. PUT, POST
• Name, e.g. Edit, Update
• MethodInfo

Alternatively, if you'd like to opt-out at the handler level, you could use a custom attribute and check for its existence in OnPageHandlerExecutionAsync:

public class SomePageFilterExcludeAttribute : Attribute { }

---

[SomePageFilterExclude]
public void OnPostUpdate() { }

---

public async Task OnPageHandlerExecutionAsync(
    PageHandlerExecutingContext ctx, PageHandlerExecutionDelegate next)
{
    var isHandlerExcluded = ctx.HandlerMethod?.MethodInfo?.
        GetCustomAttributes(typeof(SomePageFilterExcludeAttribute), false).Any() == true;

    // ...
}