Minimal Actions - array support in method signatures from querystring binding

[jchannon]

Describe the bug

When using the ASPP.NET 6 minimal hosting, querystring binding does not work with arrays/lists

To Reproduce

app.MapGet("/qs/{id:int}", HttpHandlers.GetByQueryString);

public static string GetByQueryString(int id, string name, int[] values)
{
    return id + " " + name + string.Join(",", values);
}

Adding [FromQuery(Name = "values")] to the method signature does not help either.

Exceptions (if any)

An exception is thrown when sending in a request:

curl http://localhost:5000/qs/123\?name\=dave\&values\=1\&values\=2

Unhandled exception. System.InvalidOperationException: No public static bool Int32[].TryParse(string, out Int32[]) method found for values.

Further technical details

• ASP.NET Core version 6

.NET SDK (reflecting any global.json):
 Version:   6.0.100-preview.5.21252.2
 Commit:    921395c33e

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  11.3
 OS Platform: Darwin
 RID:         osx.11.0-x64
 Base Path:   /Users/jonathan/.dotnet/sdk/6.0.100-preview.5.21252.2/

Host (useful for support):
  Version: 6.0.0-preview.5.21251.4
  Commit:  d2fba8fdc4

.NET SDKs installed:
  2.1.809 [/Users/jonathan/.dotnet/sdk]
  3.1.401 [/Users/jonathan/.dotnet/sdk]
  3.1.403 [/Users/jonathan/.dotnet/sdk]
  5.0.103 [/Users/jonathan/.dotnet/sdk]
  6.0.100-preview.5.21229.26 [/Users/jonathan/.dotnet/sdk]
  6.0.100-preview.5.21252.2 [/Users/jonathan/.dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.All 2.1.21 [/Users/jonathan/.dotnet/shared/Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.21 [/Users/jonathan/.dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.7 [/Users/jonathan/.dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.9 [/Users/jonathan/.dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.3 [/Users/jonathan/.dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.0-preview.5.21229.9 [/Users/jonathan/.dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.0-preview.5.21230.5 [/Users/jonathan/.dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.21 [/Users/jonathan/.dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.7 [/Users/jonathan/.dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.9 [/Users/jonathan/.dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.3 [/Users/jonathan/.dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.0-preview.5.21229.1 [/Users/jonathan/.dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.0-preview.5.21251.4 [/Users/jonathan/.dotnet/shared/Microsoft.NETCore.App]

To install additional .NET runtimes or SDKs:
  https://aka.ms/dotnet-download

[davidfowl]

Would this only be for simple types? Today we don't support any complex types for model binding and it conflicts with this idea

[jchannon]

Yup simple types only imo, it's a query string, you shouldn't be doing crazy stuff like json binding. I mean there's nothing stopping someone adding json in a querystring I just don't think the framework should support that

[ghost]

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[halter73]

What collection types should we support?

What should we do if we know the param comes from the route? Fail at startup? Provide a single-element array?

[DamianEdwards]

With the newly added support for BindAsync(HttpContext) on the target parameter type it would be easy to support this in the app or a library via a custom type, e.g. MultiValueQuery values, where MultiValueQuery has a BindAsync method on it.

[davidfowl]

@halter73

What collection types should we support?

This is where this typically falls of the rails. There are A LOT of collection types including custom types that implement collection interfaces. It's possible we can do something like pattern match a .Add method similar to what the ConfigurationBinder does.

This currently also conflicts with JSON bodies sent as arrays so it would need to be explicitly declared as [FromQuery] in order to make this work.

@JamesNK I'd like your feedback here.

What should we do if we know the param comes from the route? Fail at startup? Provide a single-element array?

I think fail. This should work for headers and query but not route.

Open questions:

• I'm assuming we'd support things that have TryParse but not BindAsync?
• We only want to support the syntax where there are repeated items in the query string with different values (e.g. ?a=1&a=2&a=3) can be bound to MapGet("/", (int[] a) => { }). MVC supports a superset of this syntax for arbitrary collection types (https://docs.microsoft.com/en-us/aspnet/core/mvc/models/model-binding?view=aspnetcore-6.0#collections) that minimal wouldn't support.

Reasons to avoid anything except for arrays in this scenario:

• It makes the code simpler (yay)
• It is more trimming friendly, we don't need to MakeGenericType on BCL types (I know we're forced to do this today for ValueTask<T> and Task<T> but we can keep it isolated). We just need to keep T[] instead of List<T> and we don't need to do crazy things to call Add on concrete types VS abstractions etc. etc.

So strawman proposal is:

• Only arrays (T[])
• Supports TryParse with the value of the query string parameter
• Support string[]
• Explicit sources are required for requests that do infer a body (POST/PUT/PATCH) (e.g. [FromQuery], [FromHeader])
• Implicit binding is supported for methods that do not infer a body (GET/HEAD/DELETE)
• If there are no values we pass an empty array unless the user makes the array nullable.

[davidfowl]

@jchannon This is supported in .NET 7 preview1

[davidfowl]

I mean preview2

[legistek]

Previously (in Framework) you could serialize an array of primitives to a JSON object in the query string like this:

?values=[1,2,3,4,5]

(escaped obviously)

and the method:

DoSomething(int[] values)

would bind correctly. That doesn't appear to be the case in .NET6 (or possibly earlier). I assume that was a known breaking change but I thought it worth asking? If it was not an intentional change then it's a different bug I guess.

[davidfowl]

This issue isn't about MVC's binding semantics and minimal API supports a subset of what MVC supports. If you want to see what is supported for MVC today look at https://docs.microsoft.com/en-us/aspnet/core/mvc/models/model-binding?view=aspnetcore-6.0#collections

[legistek]

Thanks. Sorry this seemed like the closest issue to what I'm experiencing that wasn't locked by the bots.

[davidfowl]

Thanks. Sorry this seemed like the closest issue to what I'm experiencing that wasn't locked by the bots.

😄. FWIW, it's not supported in MVC either, that's by design.