Fix incorrect SelectList selected item documentation and misleading comments

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();
         }

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();
         }

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();
         }

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();
         }       

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();
         }

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();
         }

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();
         }

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();
         }

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();
         }

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();
         }       

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();
         }

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();
         }       

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: