1 sentence of code, get asp Net core binds multiple sources to the same class

problem

A group of friends want to bind the information in the route to a Dto In the object ：

public class DDDDDto
{
    [FromRoute(Name ="collectionId")]
    public Guid collectionId { get; set; }
    [BindProperty(Name = "relativeUrl")]
    public string relativeUrl { get; set; }
}

So there's no need to Action A bunch of parameters are defined in ：

[HttpGet("collections/{collectionId}/patn/{relativeUrl}/children", Name = "QueryChildrenOfItem")]
public async Task<DDDDDto> QueryChildren(
    [FromRoute(Name = "collectionId")] Guid collectionId,
    [FromRoute(Name = "relativeUrl")] string relativeUrl)

Good idea. , Right ！

But the actual operation , But I found that I couldn't achieve the desired effect , Not bound to data ：

This explanation ASP.NET Core By default, you cannot bind other different sources to a single class .

Can you change the way , To solve this problem ？

Source code exploration

First , Let's look at the source code , Want to see FromRouteAttribute How it works .

Only in InferParameterBindingInfoConvention Class found a call ：

var message = Resources.FormatApiController_MultipleBodyParametersFound(
    action.DisplayName,
    nameof(FromQueryAttribute),
    nameof(FromRouteAttribute),
    nameof(FromBodyAttribute));

message += Environment.NewLine + parameters;
throw new InvalidOperationException(message);

result , This code is also used to generate exception information ！？

however , The previous part of this code caught our attention ：

This is obviously setting the binding source information ：

bindingSource = InferBindingSourceForParameter(parameter);
 
parameter.BindingInfo = parameter.BindingInfo ?? new BindingInfo();
parameter.BindingInfo.BindingSource = bindingSource;

InferBindingSourceForParameter The implementation code of is as follows ：

internal BindingSource InferBindingSourceForParameter(ParameterModel parameter)
{
    if (IsComplexTypeParameter(parameter))
    {
        if (_serviceProviderIsService?.IsService(parameter.ParameterType) is true)
        {
            return BindingSource.Services;
        }

        return BindingSource.Body;
    }

    if (ParameterExistsInAnyRoute(parameter.Action, parameter.ParameterName))
    {
        return BindingSource.Path;
    }

    return BindingSource.Query;
}

A single class must be IsComplexTypeParameter, This will cause the method to return BindingSource.Body.

This also just explains : Under normal circumstances , If you use a single class as Action Parameters , The default from the Body Reason for source binding .

that , Can you change ASP.NET Core This default binding behavior ？

One good thing came out of

Keep looking at InferParameterBindingInfoConvention Use , We found its call , Actually in a conditional branch ：

if (!options.SuppressInferBindingSourcesForParameters)
{
    var serviceProviderIsService = serviceProvider.GetService<IServiceProviderIsService>();
    var convention = options.DisableImplicitFromServicesParameters || serviceProviderIsService is null ?
        new InferParameterBindingInfoConvention(modelMetadataProvider) :
        new InferParameterBindingInfoConvention(modelMetadataProvider, serviceProviderIsService);
    ActionModelConventions.Add(convention);
}

that , If you allow SuppressInferBindingSourcesForParameters Set to true, What effect will it have ？

builder.Services.Configure<ApiBehaviorOptions>(options =>
{
    options.SuppressInferBindingSourcesForParameters = true;
});

below , It's a time to witness miracles :

We also tried from other sources , such as Query, To transfer data , Can be bound normally .

1 Sentence code , We've got it ASP.NET Core The ability to bind multiple sources to the same class .

Conclusion

later , We're in the official file （https://docs.microsoft.com/zh-cn/aspnet/core/web-api/?view=aspnetcore-6.0） I found an explanation ：

When not explicitly specified on the parameter [FromXXX] when ,ASP.NET Core Can perform binding source reasoning , For example, it will be inferred that the binding source of a single class is Body.

Set up SuppressInferBindingSourcesForParameter by true, Will disable binding source inference .ASP.NET Core The runtime will try to pull data from all sources in order for binding .

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