From 486e94f93b8854411e52939b14bfcf84844e65de Mon Sep 17 00:00:00 2001
From: "jason.zhu" <jason.zhu@xero.com>
Date: Wed, 16 Jun 2021 16:19:37 +1000
Subject: [PATCH] Finished 'Attribute Route Constraints in ASP.NET MVC'

---
 2_Routing.md | 46 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 45 insertions(+), 1 deletion(-)

diff --git a/2_Routing.md b/2_Routing.md
index 64e6def..807f6ea 100644
--- a/2_Routing.md
+++ b/2_Routing.md
@@ -391,4 +391,48 @@ namespace AttributeRoutingDemoInMVC.Controllers
     }
 }
 ```
-This will overwrite `"students"` route prefix.
\ No newline at end of file
+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**
\ No newline at end of file