In the previous exercise we typed out each parameter name in the form, then copied them over to the OnPost() method, then set them equal to properties. In some cases, we would need a fourth step to convert each value into a valid .NET type…

ASP.NET Core provides a feature that takes care of all that for us: model binding. In model binding, data is retrieved from an HTTP request, it is converted into .NET types, and it is stored in corresponding model properties.

To activate model binding in a page model, make sure that the desired property name matches the name attribute in the <form>, then label it with the attribute [BindProperty].

In the view page:

<form method="post">
  <div class="form-group">
    <label for="Title">Title</label>
    <input type="text" class="form-control" id="Title" name="Title" placeholder="Title">
  </div>
  <div class="form-group">
    <label for="Author">Author</label>
    <input type="text" class="form-control" id="Author" name="Author" placeholder="Author">
  </div>
  <button type="submit" class="btn btn-primary">Submit</button>
</form>

In the page model:

[BindProperty]
string Title { get; set; }

[BindProperty]
string Author { get; set; }

We can then remove the method parameters and assume that the submitted form values are set to their corresponding properties:

// No more method parameters!
// No more Author = author!
public void OnPost()
{ }

You might not be familiar with attributes in C#, but that’s okay. All you need to know is that the line [BindProperty] goes directly above each property.

Technically, you also need to use the Microsoft.AspNetCore.Mvc namespace, but that is included in default ASP.NET templates. If you’d like to learn more, read about model binding in the Microsoft documentation.