Fix incorrect SelectList selected item documentation and misleading comments (#36032)

Copilot · tdykstra · web-flow · commit 6e499c100954 · 2025-10-13T10:07:10.000-07:00
* Initial plan

* Fix SelectList selected item documentation and misleading comments

Co-authored-by: tdykstra &lt;1569635+tdykstra@users.noreply.github.com&gt;

---------

Co-authored-by: copilot-swe-agent[bot] &lt;198982749+Copilot@users.noreply.github.com&gt;
Co-authored-by: tdykstra &lt;1569635+tdykstra@users.noreply.github.com&gt;
diff --git a/aspnetcore/data/ef-rp/intro/samples/cu-completed-stages/part7/ContosoUniversity/Pages/Courses/Create.cshtml.cs b/aspnetcore/data/ef-rp/intro/samples/cu-completed-stages/part7/ContosoUniversity/Pages/Courses/Create.cshtml.cs
@@ -43,7 +43,7 @@ public async Task<IActionResult> OnPostAsync()
                 return RedirectToPage("./Index");
             }
 
-            // Select DepartmentID if TryUpdateModelAsync fails.
+            // Repopulate departments dropdown. emptyCourse.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, emptyCourse.DepartmentID);
             return Page();
         }
diff --git a/aspnetcore/data/ef-rp/intro/samples/cu-completed-stages/part7/ContosoUniversity/Pages/Courses/Edit.cshtml.cs b/aspnetcore/data/ef-rp/intro/samples/cu-completed-stages/part7/ContosoUniversity/Pages/Courses/Edit.cshtml.cs
@@ -32,7 +32,7 @@ public async Task<IActionResult> OnGetAsync(int? id)
                 return NotFound();
             }
 
-            // Select current DepartmentID.
+            // Populate departments dropdown. Course.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, Course.DepartmentID);
             return Page();
         }
@@ -60,7 +60,7 @@ public async Task<IActionResult> OnPostAsync(int? id)
                 return RedirectToPage("./Index");
             }
 
-            // Select DepartmentID if TryUpdateModelAsync fails.
+            // Repopulate departments dropdown. courseToUpdate.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, courseToUpdate.DepartmentID);
             return Page();
         }
diff --git a/aspnetcore/data/ef-rp/intro/samples/cu/Pages/Courses/Create.cshtml.cs b/aspnetcore/data/ef-rp/intro/samples/cu/Pages/Courses/Create.cshtml.cs
@@ -41,7 +41,7 @@ public async Task<IActionResult> OnPostAsync()
                 return RedirectToPage("./Index");
             }
 
-            // Select DepartmentID if TryUpdateModelAsync fails.
+            // Repopulate departments dropdown. emptyCourse.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, emptyCourse.DepartmentID);
             return Page();
         }
diff --git a/aspnetcore/data/ef-rp/intro/samples/cu/Pages/Courses/Edit.cshtml.cs b/aspnetcore/data/ef-rp/intro/samples/cu/Pages/Courses/Edit.cshtml.cs
@@ -32,7 +32,7 @@ public async Task<IActionResult> OnGetAsync(int? id)
                 return NotFound();
             }
 
-            // Select current DepartmentID.
+            // Populate departments dropdown. Course.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context,Course.DepartmentID);
             return Page();
         }
@@ -55,7 +55,7 @@ public async Task<IActionResult> OnPostAsync(int? id)
                 return RedirectToPage("./Index");
             }
 
-            // Select DepartmentID if TryUpdateModelAsync fails.
+            // Repopulate departments dropdown. courseToUpdate.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, courseToUpdate.DepartmentID);
             return Page();
         }       
diff --git a/aspnetcore/data/ef-rp/intro/samples/cu20snapshots/cu-part7/Pages/Courses/Create.cshtml.cs b/aspnetcore/data/ef-rp/intro/samples/cu20snapshots/cu-part7/Pages/Courses/Create.cshtml.cs
@@ -53,7 +53,7 @@ public async Task<IActionResult> OnPostAsync()
                 return RedirectToPage("./Index");
             }
 
-            // Select DepartmentID if TryUpdateModelAsync fails.
+            // Repopulate departments dropdown. emptyCourse.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, emptyCourse.DepartmentID);
             return Page();
         }
diff --git a/aspnetcore/data/ef-rp/intro/samples/cu20snapshots/cu-part7/Pages/Courses/Edit.cshtml.cs b/aspnetcore/data/ef-rp/intro/samples/cu20snapshots/cu-part7/Pages/Courses/Edit.cshtml.cs
@@ -38,7 +38,7 @@ public async Task<IActionResult> OnGetAsync(int? id)
                 return NotFound();
             }
 
-            // Select current DepartmentID.
+            // Populate departments dropdown. Course.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, Course.DepartmentID);
             return Page();
         }
@@ -61,7 +61,7 @@ public async Task<IActionResult> OnPostAsync(int? id)
                 return RedirectToPage("./Index");
             }
 
-            // Select DepartmentID if TryUpdateModelAsync fails.
+            // Repopulate departments dropdown. courseToUpdate.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, courseToUpdate.DepartmentID);
             return Page();
         }
diff --git a/aspnetcore/data/ef-rp/intro/samples/cu20snapshots/cu-part8/Pages/Courses/Create.cshtml.cs b/aspnetcore/data/ef-rp/intro/samples/cu20snapshots/cu-part8/Pages/Courses/Create.cshtml.cs
@@ -53,7 +53,7 @@ public async Task<IActionResult> OnPostAsync()
                 return RedirectToPage("./Index");
             }
 
-            // Select DepartmentID if TryUpdateModelAsync fails.
+            // Repopulate departments dropdown. emptyCourse.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, emptyCourse.DepartmentID);
             return Page();
         }
diff --git a/aspnetcore/data/ef-rp/intro/samples/cu20snapshots/cu-part8/Pages/Courses/Edit.cshtml.cs b/aspnetcore/data/ef-rp/intro/samples/cu20snapshots/cu-part8/Pages/Courses/Edit.cshtml.cs
@@ -38,7 +38,7 @@ public async Task<IActionResult> OnGetAsync(int? id)
                 return NotFound();
             }
 
-            // Select current DepartmentID.
+            // Populate departments dropdown. Course.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, Course.DepartmentID);
             return Page();
         }
@@ -61,7 +61,7 @@ public async Task<IActionResult> OnPostAsync(int? id)
                 return RedirectToPage("./Index");
             }
 
-            // Select DepartmentID if TryUpdateModelAsync fails.
+            // Repopulate departments dropdown. courseToUpdate.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, courseToUpdate.DepartmentID);
             return Page();
         }
diff --git a/aspnetcore/data/ef-rp/intro/samples/cu30/Pages/Courses/Create.cshtml.cs b/aspnetcore/data/ef-rp/intro/samples/cu30/Pages/Courses/Create.cshtml.cs
@@ -36,7 +36,7 @@ public async Task<IActionResult> OnPostAsync()
                 return RedirectToPage("./Index");
             }
 
-            // Select DepartmentID if TryUpdateModelAsync fails.
+            // Repopulate departments dropdown. emptyCourse.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, emptyCourse.DepartmentID);
             return Page();
         }
diff --git a/aspnetcore/data/ef-rp/intro/samples/cu30/Pages/Courses/Edit.cshtml.cs b/aspnetcore/data/ef-rp/intro/samples/cu30/Pages/Courses/Edit.cshtml.cs
@@ -32,7 +32,7 @@ public async Task<IActionResult> OnGetAsync(int? id)
                 return NotFound();
             }
 
-            // Select current DepartmentID.
+            // Populate departments dropdown. Course.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, Course.DepartmentID);
             return Page();
         }
@@ -60,7 +60,7 @@ public async Task<IActionResult> OnPostAsync(int? id)
                 return RedirectToPage("./Index");
             }
 
-            // Select DepartmentID if TryUpdateModelAsync fails.
+            // Repopulate departments dropdown. courseToUpdate.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, courseToUpdate.DepartmentID);
             return Page();
         }       
diff --git a/aspnetcore/data/ef-rp/intro/samples/cu50/Pages/Courses/Create.cshtml.cs b/aspnetcore/data/ef-rp/intro/samples/cu50/Pages/Courses/Create.cshtml.cs
@@ -36,7 +36,7 @@ public async Task<IActionResult> OnPostAsync()
                 return RedirectToPage("./Index");
             }
 
-            // Select DepartmentID if TryUpdateModelAsync fails.
+            // Repopulate departments dropdown. emptyCourse.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, emptyCourse.DepartmentID);
             return Page();
         }
diff --git a/aspnetcore/data/ef-rp/intro/samples/cu50/Pages/Courses/Edit.cshtml.cs b/aspnetcore/data/ef-rp/intro/samples/cu50/Pages/Courses/Edit.cshtml.cs
@@ -32,7 +32,7 @@ public async Task<IActionResult> OnGetAsync(int? id)
                 return NotFound();
             }
 
-            // Select current DepartmentID.
+            // Populate departments dropdown. Course.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, Course.DepartmentID);
             return Page();
         }
@@ -60,7 +60,7 @@ public async Task<IActionResult> OnPostAsync(int? id)
                 return RedirectToPage("./Index");
             }
 
-            // Select DepartmentID if TryUpdateModelAsync fails.
+            // Repopulate departments dropdown. courseToUpdate.DepartmentID determines the selected item.
             PopulateDepartmentsDropDownList(_context, courseToUpdate.DepartmentID);
             return Page();
         }       
diff --git a/aspnetcore/data/ef-rp/update-related-data.md b/aspnetcore/data/ef-rp/update-related-data.md
@@ -30,8 +30,10 @@ Create a `Pages/Courses/DepartmentNamePageModel.cs` file with the following code
 
 [!code-csharp[](intro/samples/cu50/Pages/Courses/DepartmentNamePageModel.cs)]
 
-The preceding code creates a <xref:Microsoft.AspNetCore.Mvc.Rendering.SelectList> to contain the list of department names. If `selectedDepartment` is specified, that department is selected in the `SelectList`.
+The preceding code creates a <xref:Microsoft.AspNetCore.Mvc.Rendering.SelectList> to contain the list of department names. The `selectedDepartment` parameter allows the calling code to specify the item that will be selected when the drop-down list is rendered. However, when using the Select Tag Helper with `asp-for`, the selected item is determined by the model property value (such as `Course.DepartmentID`), not by the `selectedDepartment` parameter.
 
+> [!IMPORTANT]
+> When using the Select Tag Helper with `asp-for="Course.DepartmentID"`, the selected option is automatically determined by the value of `Course.DepartmentID`. The `selectedDepartment` parameter passed to the SelectList constructor is ignored in this scenario.
 The Create and Edit page model classes will derive from `DepartmentNamePageModel`.
 
 ### Update the Course Create page model
@@ -77,7 +79,7 @@ Update `Pages/Courses/Edit.cshtml.cs` with the following code:
 
 [!code-csharp[](intro/samples/cu50/Pages/Courses/Edit.cshtml.cs?highlight=8,28,35,36,40-66)]
 
-The changes are similar to those made in the Create page model. In the preceding code, `PopulateDepartmentsDropDownList` passes in the department ID, which selects that department in the drop-down list.
+The changes are similar to those made in the Create page model. In the preceding code, `PopulateDepartmentsDropDownList` passes in the department ID. When using the Select Tag Helper with `asp-for="Course.DepartmentID"`, the selected item in the drop-down list is determined by the value of `Course.DepartmentID`, not by the `selectedDepartment` parameter passed to the SelectList constructor.
 
 ### Update the Course Edit Razor page
 
@@ -253,7 +255,7 @@ Create a `Pages/Courses/DepartmentNamePageModel.cs` file with the following code
 
 [!code-csharp[](intro/samples/cu30/Pages/Courses/DepartmentNamePageModel.cs)]
 
-The preceding code creates a <xref:Microsoft.AspNetCore.Mvc.Rendering.SelectList> to contain the list of department names. If `selectedDepartment` is specified, that department is selected in the `SelectList`.
+The preceding code creates a <xref:Microsoft.AspNetCore.Mvc.Rendering.SelectList> to contain the list of department names. The `selectedDepartment` parameter allows the calling code to specify the item that will be selected when the drop-down list is rendered. However, when using the Select Tag Helper with `asp-for`, the selected item is determined by the model property value (such as `Course.DepartmentID`), not by the `selectedDepartment` parameter.
 
 The Create and Edit page model classes will derive from `DepartmentNamePageModel`.
 
@@ -300,7 +302,7 @@ Update `Pages/Courses/Edit.cshtml.cs` with the following code:
 
 [!code-csharp[](intro/samples/cu30/Pages/Courses/Edit.cshtml.cs?highlight=8,28,35,36,40-66)]
 
-The changes are similar to those made in the Create page model. In the preceding code, `PopulateDepartmentsDropDownList` passes in the department ID, which selects that department in the drop-down list.
+The changes are similar to those made in the Create page model. In the preceding code, `PopulateDepartmentsDropDownList` passes in the department ID. When using the Select Tag Helper with `asp-for="Course.DepartmentID"`, the selected item in the drop-down list is determined by the value of `Course.DepartmentID`, not by the `selectedDepartment` parameter passed to the SelectList constructor.
 
 ### Update the Course Edit Razor page
 
@@ -470,7 +472,7 @@ The Courses/Create and Courses/Edit pages each need a list of department names.
 
 [!code-csharp[](intro/samples/cu/Pages/Courses/DepartmentNamePageModel.cshtml.cs?highlight=9,11,20-21)]
 
-The preceding code creates a <xref:Microsoft.AspNetCore.Mvc.Rendering.SelectList> to contain the list of department names. If `selectedDepartment` is specified, that department is selected in the `SelectList`.
+The preceding code creates a <xref:Microsoft.AspNetCore.Mvc.Rendering.SelectList> to contain the list of department names. The `selectedDepartment` parameter allows the calling code to specify the item that will be selected when the drop-down list is rendered. However, when using the Select Tag Helper with `asp-for`, the selected item is determined by the model property value (such as `Course.DepartmentID`), not by the `selectedDepartment` parameter.
 
 The Create and Edit page model classes will derive from `DepartmentNamePageModel`.
 
@@ -517,7 +519,7 @@ Replace the code in `Pages/Courses/Edit.cshtml.cs` with the following code:
 
 [!code-csharp[](intro/samples/cu/Pages/Courses/Edit.cshtml.cs?highlight=8,28,35,36,40,47-999)]
 
-The changes are similar to those made in the Create page model. In the preceding code, `PopulateDepartmentsDropDownList` passes in the department ID, which select the department specified in the drop-down list.
+The changes are similar to those made in the Create page model. In the preceding code, `PopulateDepartmentsDropDownList` passes in the department ID. When using the Select Tag Helper with `asp-for="Course.DepartmentID"`, the selected item in the drop-down list is determined by the value of `Course.DepartmentID`, not by the `selectedDepartment` parameter passed to the SelectList constructor.
 
 Update `Pages/Courses/Edit.cshtml` with the following markup:
 

Original file line number	Diff line number	Diff line change
`@@ -43,7 +43,7 @@ public async Task<IActionResult> OnPostAsync()`
`43`	`43`	`return RedirectToPage("./Index");`
`44`	`44`	`}`
`45`	`45`
`46`		`- // Select DepartmentID if TryUpdateModelAsync fails.`
	`46`	`+ // Repopulate departments dropdown. emptyCourse.DepartmentID determines the selected item.`
`47`	`47`	`PopulateDepartmentsDropDownList(_context, emptyCourse.DepartmentID);`
`48`	`48`	`return Page();`
`49`	`49`	`}`
Original file line number	Diff line number	Diff line change
`@@ -32,7 +32,7 @@ public async Task<IActionResult> OnGetAsync(int? id)`
`32`	`32`	`return NotFound();`
`33`	`33`	`}`
`34`	`34`
`35`		`- // Select current DepartmentID.`
	`35`	`+ // Populate departments dropdown. Course.DepartmentID determines the selected item.`
`36`	`36`	`PopulateDepartmentsDropDownList(_context, Course.DepartmentID);`
`37`	`37`	`return Page();`
`38`	`38`	`}`
`@@ -60,7 +60,7 @@ public async Task<IActionResult> OnPostAsync(int? id)`
`60`	`60`	`return RedirectToPage("./Index");`
`61`	`61`	`}`
`62`	`62`
`63`		`- // Select DepartmentID if TryUpdateModelAsync fails.`
	`63`	`+ // Repopulate departments dropdown. courseToUpdate.DepartmentID determines the selected item.`
`64`	`64`	`PopulateDepartmentsDropDownList(_context, courseToUpdate.DepartmentID);`
`65`	`65`	`return Page();`
`66`	`66`	`}`
Original file line number	Diff line number	Diff line change
`@@ -41,7 +41,7 @@ public async Task<IActionResult> OnPostAsync()`
`41`	`41`	`return RedirectToPage("./Index");`
`42`	`42`	`}`
`43`	`43`
`44`		`- // Select DepartmentID if TryUpdateModelAsync fails.`
	`44`	`+ // Repopulate departments dropdown. emptyCourse.DepartmentID determines the selected item.`
`45`	`45`	`PopulateDepartmentsDropDownList(_context, emptyCourse.DepartmentID);`
`46`	`46`	`return Page();`
`47`	`47`	`}`
Original file line number	Diff line number	Diff line change
`@@ -53,7 +53,7 @@ public async Task<IActionResult> OnPostAsync()`
`53`	`53`	`return RedirectToPage("./Index");`
`54`	`54`	`}`
`55`	`55`
`56`		`- // Select DepartmentID if TryUpdateModelAsync fails.`
	`56`	`+ // Repopulate departments dropdown. emptyCourse.DepartmentID determines the selected item.`
`57`	`57`	`PopulateDepartmentsDropDownList(_context, emptyCourse.DepartmentID);`
`58`	`58`	`return Page();`
`59`	`59`	`}`
Original file line number	Diff line number	Diff line change
`@@ -38,7 +38,7 @@ public async Task<IActionResult> OnGetAsync(int? id)`
`38`	`38`	`return NotFound();`
`39`	`39`	`}`
`40`	`40`
`41`		`- // Select current DepartmentID.`
	`41`	`+ // Populate departments dropdown. Course.DepartmentID determines the selected item.`
`42`	`42`	`PopulateDepartmentsDropDownList(_context, Course.DepartmentID);`
`43`	`43`	`return Page();`
`44`	`44`	`}`
`@@ -61,7 +61,7 @@ public async Task<IActionResult> OnPostAsync(int? id)`
`61`	`61`	`return RedirectToPage("./Index");`
`62`	`62`	`}`
`63`	`63`
`64`		`- // Select DepartmentID if TryUpdateModelAsync fails.`
	`64`	`+ // Repopulate departments dropdown. courseToUpdate.DepartmentID determines the selected item.`
`65`	`65`	`PopulateDepartmentsDropDownList(_context, courseToUpdate.DepartmentID);`
`66`	`66`	`return Page();`
`67`	`67`	`}`
Original file line number	Diff line number	Diff line change
`@@ -36,7 +36,7 @@ public async Task<IActionResult> OnPostAsync()`
`36`	`36`	`return RedirectToPage("./Index");`
`37`	`37`	`}`
`38`	`38`
`39`		`- // Select DepartmentID if TryUpdateModelAsync fails.`
	`39`	`+ // Repopulate departments dropdown. emptyCourse.DepartmentID determines the selected item.`
`40`	`40`	`PopulateDepartmentsDropDownList(_context, emptyCourse.DepartmentID);`
`41`	`41`	`return Page();`
`42`	`42`	`}`