AspNetCore.Docs/aspnetcore/includes/RP/da2.md

We'll cover DataAnnotations in the next tutorial. The Display attribute specifies what to display for the name of a field (in this case "Release Date" instead of "ReleaseDate"). The DataType attribute specifies the type of the data (Date), so the time information stored in the field isn't displayed.

Browse to Pages/Movies and hover over an Edit link to see the target URL.

The Edit, Details, and Delete links are generated by the Anchor Tag Helper in the Pages/Movies/Index.cshtml file.

[!code-cshtmlMain]

Tag Helpers enable server-side code to participate in creating and rendering HTML elements in Razor files. In the preceding code, the AnchorTagHelper dynamically generates the HTML href attribute value from the Razor Page (the route is relative), the asp-page, and the route id (asp-route-id). See URL generation for Pages for more information.

Use View Source from your favorite browser to examine the generated markup. A portion of the generated HTML is shown below:

<td>
  <a href="/Movies/Edit?id=1">Edit</a> |
  <a href="/Movies/Details?id=1">Details</a> |
  <a href="/Movies/Delete?id=1">Delete</a>
</td>

The dynamically-generated links pass the movie ID with a query string (for example, http://localhost:5000/Movies/Details?id=2 ).

Update the Edit, Details, and Delete Razor Pages to use the "{id:int}" route template. Change the page directive for each of these pages from @page to @page "{id:int}". Run the app and then view source. The generated HTML adds the ID to the path portion of the URL:

<td>
  <a href="/Movies/Edit/1">Edit</a> |
  <a href="/Movies/Details/1">Details</a> |
  <a href="/Movies/Delete/1">Delete</a>
</td>

A request to the page with the "{id:int}" route template that does not include the integer will return an HTTP 404 (not found) error. For example, http://localhost:5000/Movies/Details will return a 404 error. To make the ID optional, append ? to the route constraint:

@page "{id:int?}"

Update concurrency exception handling

Update the OnPostAsync method in the Pages/Movies/Edit.cshtml.cs file. The following highlighted code shows the changes:

[!code-csharpMain]

The previous code only detects concurrency exceptions when the first concurrent client deletes the movie, and the second concurrent client posts changes to the movie.

To test the catch block:

• Set a breakpoint on catch (DbUpdateConcurrencyException)
• Edit a movie.
• In another browser window, select the Delete link for the same movie, and then delete the movie.
• In the previous browser window, post changes to the movie.

Production code would generally detect concurrency conflicts when two or more clients concurrently updated a record. See Handling concurrency conflicts for more information.

Posting and binding review

Examine the Pages/Movies/Edit.cshtml.cs file: [!code-csharpMain]

When an HTTP GET request is made to the Movies/Edit page (for example, http://localhost:5000/Movies/Edit/2):

• The OnGetAsync method fetches the movie from the database and returns the Page method.
• The Page method renders the Pages/Movies/Edit.cshtml Razor Page. The Pages/Movies/Edit.cshtml file contains the model directive (@model RazorPagesMovie.Pages.Movies.EditModel), which makes the movie model available on the page.
• The Edit form is displayed with the values from the movie.

When the Movies/Edit page is posted:

• The form values on the page are bound to the Movie property. The [BindProperty] attribute enables Model binding.

  [BindProperty]
  public Movie Movie { get; set; }
  

• If there are errors in the model state (for example, ReleaseDate cannot be converted to a date), the form is posted again with the submitted values.

• If there are no model errors, the movie is saved.

The HTTP GET methods in the Index, Create, and Delete Razor pages follow a similar pattern. The HTTP POST OnPostAsync method in the Create Razor Page follows a similar pattern to the OnPostAsync method in the Edit Razor Page.

Search is added in the next tutorial.