Handle forms with Blazor SSR

[javiercn]

This needs design.

• How do we map the form from the HTML to an action on the app.
• How do we bind the form data to the app state for processing.
• Support for antiforgery.
• Support for server side rendered patterns (PRG).

Mapping form data specifically.

• Declarative binding
• Primitive values
• Collections
• Dictionaries
• Complex types
• Recursive complex types
• Error handling
• Globalization
• Security
• Extensibility
  • Ignored properties.
  • Changing the property name.
  • Required properties.
  • Custom converters for a given property.
• Converter source generation
• Optimization
  • Removing allocations during prefix computation.
  • Removing allocations from reading the form.
  • Optimized form data structure for common form sizes
    • Evaluate using a list instead of a dictionary for small sets of keys. AdaptiveCapacityDictionary
    • Filtering out keys we don't care about when reading the dictionary.
    • Sizing the dictionary ahead of time to avoid resizing it.
    • Inlining implementation for primitive types (bypass the converter)
    • Avoid allocating a prefix collection when there is only one dictionary on the type hierarchy (since will only process a single set of keys).

[RyoukoKonpaku]

Is it possible perhaps to link the form post to a specific method? You could possibly determine which method to wireup as an action method by looking at the edit form's @OnSubmit. This should make it a bit more intuitive and also easier to support multiple forms in a page. A similar method is supported on razor pages via the asp-page-handler="Method" tag helper.

The callback method could even allow an EditContext<TModel> parameter so the form can be validated on that method or even the usual razor pages model binding (e.g. IFormFile, IFormCollection) if you want a purely SSR component.

The model binding could check the callback parameter's TModel and bind it to any available component parameter that has the same type.

I'm imagining something like this:

<EditForm Model="@Form " method="post" OnSubmit="OnPost1">
    <InputTextArea name="review" rows="5" Value="@Form.Text" />
    <ValidationMessage For="() => Form.Text" />
</EditForm>

<EditForm Model="@Form2" method="post" OnSubmit="OnPost2">
     @* Form2 usage here *@
</EditForm>

@code {
    [Parameter] public TModel Form { get; set; }
    [Parameter] public TModel2 Form2 { get; set; }

    public async Task OnPost1(EditContext<TModel> context) 
    {
         if(context.Validated())
         {
              // Logic goes here
         }
    }

    public async Task OnPost2(EditContext<TModel2> context)
    {

    }
}

[javiercn]

@RyoukoKonpaku thanks for the input.

We already have a similar design that I prototyped but that we have not shared yet as is still a WIP, there are some differences to what you are proposing, but the idea is similar.

[RyoukoKonpaku]

@javiercn Great to hear, I'll definitely be looking forward for those updates.

Thanks for contacting us.

We're moving this issue to the .NET 8 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.