Add OpenAPI support for custom JSON:API action methods

docs/build-dev.ps1

@@ -4,7 +4,9 @@
 
 param(
     # Specify -NoBuild to skip code build and examples generation. This runs faster, so handy when only editing Markdown files.
-    [switch] $NoBuild=$False
+    [switch] $NoBuild=$False,
+    # Specify -NoOpen to skip opening the documentation website in a web browser.
+    [switch] $NoOpen=$False
 )
 
 function VerifySuccessExitCode {
@@ -53,9 +55,12 @@ Copy-Item -Force -Recurse home/assets/* _site/styles/
 
 cd _site
 $webServerJob = httpserver &
-Start-Process "http://localhost:8080/"
 cd ..
 
+if (-Not $NoOpen) {
+    Start-Process "http://localhost:8080/"
+}
+
 Write-Host ""
 Write-Host "Web server started. Press Enter to close."
 $key = [Console]::ReadKey()

docs/usage/extensibility/controllers.md

@@ -137,3 +137,56 @@ public class ReportsController : JsonApiController<Report, int>
 ```
 
 For more information about resource service injection, see [Replacing injected services](~/usage/extensibility/layer-overview.md#replacing-injected-services) and [Resource Services](~/usage/extensibility/services.md).
+
+## Custom action methods
+
+Aside from adding custom ASP.NET controllers and Minimal API endpoints to your project that are unrelated to JSON:API,
+you can also augment JsonApiDotNetCore controllers with custom action methods.
+This applies to both auto-generated and explicit controllers.
+
+When doing so, they participate in the JsonApiDotNetCore pipeline, which means that JSON:API query string parameters are available,
+exceptions are handled, and the request/response bodies match the JSON:API structure. As a result, the following restrictions apply:
+
+- The input/output resource types used must exist in the resource graph.
+- For primary endpoints, the input/output resource types must match the controller resource type.
+- An action method can only return a resource, a collection of resources, an error, or null.
+
+For example, the following custom POST endpoint doesn't take a request body and returns a collection of resources:
+
+```c#
+partial class TagsController
+{
+    // POST /tags/defaults
+    [HttpPost("defaults")]
+    public async Task<IActionResult> CreateDefaultTagsAsync()
+    {
+        List<string> defaultTagNames =
+        [
+            "Create design",
+            "Implement feature",
+            "Write tests",
+            "Update documentation",
+            "Deploy changes"
+        ];
+
+        bool hasDefaultTags = await _appDbContext.Tags.AnyAsync(tag => defaultTagNames.Contains(tag.Name));
+        if (hasDefaultTags)
+        {
+            throw new JsonApiException(new ErrorObject(HttpStatusCode.Conflict)
+            {
+                Title = "Default tags already exist."
+            });
+        }
+
+        List<Tag> defaultTags = defaultTagNames.Select(name => new Tag
+        {
+            Name = name
+        }).ToList();
+
+        _appDbContext.Tags.AddRange(defaultTags);
+        await _appDbContext.SaveChangesAsync();
+
+        return Ok(defaultTags);
+    }
+}
+```

docs/usage/openapi.md

@@ -37,10 +37,13 @@ provides OpenAPI support for JSON:API by integrating with [Swashbuckle](https://
 
 By default, the OpenAPI document will be available at `http://localhost:<port>/swagger/v1/swagger.json`.
 
+> [!TIP]
+> In addition to the documentation here, various examples can be found in the [OpenApiTests project](https://github.com/json-api-dotnet/JsonApiDotNetCore/tree/master/test/OpenApiTests).
+
 ### Customizing the Route Template
 
 Because Swashbuckle doesn't properly implement the ASP.NET Options pattern, you must *not* use its
-[documented way](https://github.com/domaindrivendev/Swashbuckle.AspNetCore?tab=readme-ov-file#change-the-path-for-swagger-json-endpoints)
+[documented way](https://github.com/domaindrivendev/Swashbuckle.AspNetCore/blob/master/docs/configure-and-customize-swagger.md#change-the-path-for-swagger-json-endpoints)
 to change the route template:
 
 ```c#
@@ -78,6 +81,40 @@ The `NoWarn` line is optional, which suppresses build warnings for undocumented
   </PropertyGroup>
 ```
 
-You can combine this with the documentation that Swagger itself supports, by enabling it as described
-[here](https://github.com/domaindrivendev/Swashbuckle.AspNetCore#include-descriptions-from-xml-comments).
+You can combine this with the documentation that Swashbuckle itself supports, by enabling it as described
+[here](https://github.com/domaindrivendev/Swashbuckle.AspNetCore/blob/master/docs/configure-and-customize-swaggergen.md#include-descriptions-from-xml-comments).
 This adds documentation for additional types, such as triple-slash comments on enums used in your resource models.
+
+## Custom JSON:API action methods
+
+To express the metadata of [custom action methods](~/usage/extensibility/controllers.md#custom-action-methods) in OpenAPI,
+use the following attributes on your controller action method:
+
+- The `Name` property on `HttpMethodAttribute` to specify the OpenAPI operation ID, for example:
+  ```c#
+  [HttpGet("active", Name = "get-active-users")]
+  ```
+
+- `EndpointDescriptionAttribute` to specify the OpenAPI endpoint description, for example:
+  ```c#
+  [EndpointDescription("Provides access to user accounts.")]
+  ```
+
+- `ConsumesAttribute` to specify the resource type of the request body, for example:
+  ```c#
+  [Consumes(typeof(UserAccount), "application/vnd.api+json")]
+  ```
+  > [!NOTE]
+  > The `contentType` parameter is required, but effectively ignored.
+
+- `ProducesResponseTypeAttribute` attribute(s) to specify the response types and status codes, for example:
+  ```c#
+  [ProducesResponseType<ICollection<UserAccount>>(StatusCodes.Status200OK)]
+  [ProducesResponseType(StatusCodes.Status204NoContent)]
+  [ProducesResponseType(StatusCodes.Status404NotFound)]
+  [ProducesResponseType(StatusCodes.Status409Conflict)]
+  ```
+  > [!NOTE]
+  > For non-success response status codes, the type should be omitted.
+
+Custom parameters on action methods can be decorated with the usual attributes, such as `[Required]`, `[Description]`, etc.

src/JsonApiDotNetCore.OpenApi.Swashbuckle/ActionDescriptorExtensions.cs

@@ -7,7 +7,7 @@ namespace JsonApiDotNetCore.OpenApi.Swashbuckle;
 
 internal static class ActionDescriptorExtensions
 {
-    public static MethodInfo GetActionMethod(this ActionDescriptor descriptor)
+    public static MethodInfo? TryGetActionMethod(this ActionDescriptor descriptor)
     {
         ArgumentNullException.ThrowIfNull(descriptor);
 
@@ -16,10 +16,7 @@ public static MethodInfo GetActionMethod(this ActionDescriptor descriptor)
             return controllerActionDescriptor.MethodInfo;
         }
 
-        MethodInfo? methodInfo = descriptor.EndpointMetadata.OfType<MethodInfo>().FirstOrDefault();
-        ConsistencyGuard.ThrowIf(methodInfo == null);
-
-        return methodInfo;
+        return descriptor.EndpointMetadata.OfType<MethodInfo>().FirstOrDefault();
     }
 
     public static ControllerParameterDescriptor? GetBodyParameterDescriptor(this ActionDescriptor descriptor)

src/JsonApiDotNetCore.OpenApi.Swashbuckle/ConfigureSwaggerGenOptions.cs

@@ -146,17 +146,17 @@ private static void IncludeDerivedTypes(ResourceType baseType, List<Type> clrTyp
 
     private static IList<string> GetOpenApiOperationTags(ApiDescription description, IControllerResourceMapping controllerResourceMapping)
     {
-        var actionMethod = OpenApiActionMethod.Create(description.ActionDescriptor);
+        var actionMethod = JsonApiActionMethod.TryCreate(description.ActionDescriptor);
 
         switch (actionMethod)
         {
-            case AtomicOperationsActionMethod:
+            case OperationsActionMethod:
             {
                 return ["operations"];
             }
-            case JsonApiActionMethod jsonApiActionMethod:
+            case ResourceActionMethod resourceActionMethod:
             {
-                ResourceType? resourceType = controllerResourceMapping.GetResourceTypeForController(jsonApiActionMethod.ControllerType);
+                ResourceType? resourceType = controllerResourceMapping.GetResourceTypeForController(resourceActionMethod.ControllerType);
                 ConsistencyGuard.ThrowIf(resourceType == null);
 
                 return [resourceType.PublicName];