Finished 'Attribute Route Constraints in ASP.NET MVC'

2_Routing.md

@@ -391,4 +391,48 @@ namespace AttributeRoutingDemoInMVC.Controllers
     }
 }
 ```
-This will overwrite `"students"` route prefix.
+This will overwrite `"students"` route prefix.
+
+## Attribute Route Constraints in ASP.NET MVC
+
+### Attribute Route Constraints
+
+* **Attribute route constraints** = a set of rules that defined on routing parameters 
+* Defined by using `:` character.
+* Can add additional requirement e.g. `min()`, `max()`, `range()` etc. 
+
+e.g. We can create 2 action methods with same name with different route parameter
+
+```csharp
+namespace AttributeRoutingDemoInMVC.Controllers
+{
+    [RoutePrefix("students")]
+    public class StudentsController : Controller
+    {
+        ...
+
+        [HttpGet]
+        [Route("{studentID:int:range(1,3)}")]
+        // This will be translated to /students/2
+        public ActionResult GetStudentDetails(int studentID)
+        {
+            Student studentDetails = students.FirstOrDefault(s => s.Id == studentID);
+            return View(studentDetails);
+        }
+
+        [HttpGet]
+        [Route("{studentName:alpha}")]
+        // /student/Pranaya
+        public ActionResult GetStudentDetails(string studentName)
+        {
+            Student studentDetails = students.FirstOrDefault(s => s.Name == studentName);
+            return View(studentDetails);
+        }
+        ...
+        
+    }
+}
+```
+
+* `[Route("{studentID:int:range(1,3)}")]` enforce route engine to use this action method **only if the given studentID is integer and it's within 1,2 or 3** 
+* `[Route("{studentName:alpha}")]` enforce route engine to use this action method **only if given studentID is alphabatic character strings**